2. Earth is the fifth largest planet

Full Earth
Full Earth
The diameter of the earth at the equator is about 7926 miles, but that's not the whole story. Because the earth is not a perfect sphere but is slightly flattened at the poles, the diameter of the earth measured around the North Pole and the South Pole is about 7899 miles.

3. Earth is the only planet known to harbor life

tAll of the things we need to survive are provided under a thin layer of atmosphere that separates us from the uninhabitable void of space. Earth is made up of complex, interactive systems that are often unpredictable. Air, water, land, and life - including humans - combine forces to create a constantly changing world that we are striving to understand.

4. Earth is mostly covered in water

While the word earth is often used synonymously with dirt, seventy-one percent of the its surface is covered with water. It is the only planet where it exists in its liquid form on the surface. This is probably part of the reason that the Earth is the only planet known to contain life.

5. Early philosophy had the Earth as the center of the universe

World Globes, Shaded Relief and Colored Height
World Globes, Shaded Relief and Colored Height
though Aristarchus of Samos, in the 3rd Century B.C., figured out how to measure the distances to and sizes of the Sun and the Moon, and concluded that the Earth orbited the Sun, this view didn't attract followers until Nicolaus Copernicus, a Polish astronomer, published "On the Revolutions of the Celestial Spheres" in 1543.

6. Earth has four distinct seasons

Global Images of Earth
Global Images of Earth
Johns Hopkins UniversityThis is a result of a result of Earth's axis of rotation being tilted more than 23 degrees. Seasons changes as the tilt of Earth's axis changes during it's revolution around the Sun.

7. Earth has an atmosphere that sustains life

Pacific Ocean Surface Winds from QuikScat
Pacific Ocean Surface Winds from QuikScat
Earth's atmosphere is 77% nitrogen, 21% oxygen, with traces of argon, carbon dioxide and water. This atmosphere affects Earth's long-term climate and short-term local weather; shields us from nearly all harmful radiation coming from the Sun; and protects us from meteors as well - most of which burn up before they can strike the surface.

8. Earth has one natural satellite

Pictures of the Moon - Moon Color Composite
Pictures of the Moon - Moon Color Composite
Earth's Moon (called Luna) orbits at a distance of 384,000km, with a radius of 1738KM and a mass of 7.32e22kg. However, there are thousands of small artificial satellites which have been placed in orbit around the Earth. Also, asteroids 3753 Cruithne and 2002 AA29 have complicated orbital relationships with the Earth; they're not really moons, the term "companion" is being used.
Because of its size and rocky composition, the moon has also been called a terrestrial planet along with Mercury, Venus, Earth, and Mars. It has no atmosphere, but there is water ice in some deep craters. The moon is the only extra-planetary body that a human has visited.

9. Earth has a magnetic field

South Polar Projection of Earth
South Polar Projection of Earth
Our planet's rapid spin and molten nickel-iron core give rise to a magnetic field, which the solar wind distorts into a teardrop shape. The magnetic field does not fade off into space, but has definite boundaries. Just like the field around a magnet, ours is also polarized. When charged particles from the solar wind become trapped in Earth's magnetic field, they collide with air molecules above our planet's magnetic poles. These air molecules then begin to glow and are known as the aurorae, or the Northern and Southern Lights.

10. Our close proximity prevents us from seeing Earth in its entirety

Earthrise - Apollo 8
Earthrise - Apollo 8
Manned Spacecraft CenterTo completely view our own planet, we must leave its surface and journey into space. From the vantage point of space we are able to observe our planet globally, as we do other planets, using similar sensitive instruments to understand the delicate balance among its oceans, air, land, and life. Viewing Earth from the unique perspective of space provides the opportunity to see Earth as a whole. Scientists around the world have discovered many things about our planet by working together and sharing their findings.




week 5

The earth consists of several layers. The three main layers are the core, the mantle and the crust. The core is the inner part of the earth, the crust is the outer part and between them is the mantle. The earth is surrounded by the atmosphere. Till this moment it hasn't been possible to take a look inside the earth because the current technology doesn't allow it. Therefore all kinds of research had to be done to find out, out of which material the earth consists, what different layers there are and which influence those have (had) on the earth's surface. This research is called seismology.

Fossil fuels, coal, oil and natural gas, are a non-renewable source of energy. Formed from plants and animals that lived up to 300 million years ago, fossil fuels are found in deposits beneath the earth. The fuels are burned to release the chemical energy that is stored within this resource. Energy is essential to moden society as we know it. Over 85% of our energy demands are met by the combustion of fossil fuels. These two pie charts show exactly how vital fossil fuels are to our society by showing how much of each energy resource is consumed.
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Going back to the earlier days of Earth, the plants and animals that lived then eventually died and decomposed. The majority of these life forms were phytoplankton and zooplankton. When these ancient ocean dwellers died, they accumulated on the bottom of a seabed; this is how a good portion of our fossil fuel reserves began. The actual transformation process of these prehistoric creatures is not known, but scientists do know that the pressure, heat, and a great deal of time go into the making of fossil fuels.
Geologists are fairly certain that the beds of organic remains mixed with silt and mud to form layers. Over time, mineral sedimentation formed on top of the organisms, effectively entombing them in rock. As this occurred, pressure and temperature increased. These conditions, and possibly other unknown factors, caused organic material to break down into the simpler form of hydrocarbons: chains of carbon and hydrogen ranging from simple configuration to complex compounds. Another affect of extreme pressure is that the oil and gas which are various mixtures of hydrocarbons, migrate upwards to the surface. Exactly when in the conversion process and the nature of this migration is not known and is subject to conjecture.
external image anticline.gifOil and gas are found in the ground, not freely drifting up through the earth. This is because the hydrocarbons come across rock formations that they are unable to penetrate. Complex rock structures that effectively trap gas and oil are formed by tectonic plate activity, the same forces that shift continents. The most common formation that accomplishes this is called an anticline, a dome or arched layer of rock that is impermeable by oil and gas. Underneath this barrier, a reservoir builds up. An oil reservoir is not some vast underground lake, but rather a seemingly solid layer of rock that is porous. Oil fields have been found everywhere on the planet except for the continent of Antarctica.
These fields always contain some gas, but this natural gas, methane, does not take nearly as long to form. Natural gas is also found in independent deposits within the ground as well as from others sources too. Methane is a common gas found in swamps and is also the byproduct of animals' digestive system. Incidentally, Methane is also a greenhouse gas.
Coal is formed in a similar to the other fossil fuels, though it goes through a different process, coalification. Coal is made of decomposed plant matter in conditions of high temperature and pressure, though it takes a relatively shorter amount of time to form. Coal is not a uniform substance either, it's composition varies from deposit to deposit. Factors that cause this deviation are the types of original plant matter, and the extent the plant matter decomposed. There are over 1200 distinguishable types of coal. Coal begins as peat, a mass of dead and decomposing plant matter. Peat itself has been used as fuel in the past, as an alternative to wood. Next, the peat becomes lignite, a brownish rock that contains recognizable plant matter and has a relatively low heating value. Lignite is the halfway point from peat to coal. The next phase is subbituminous. A shade of dull black, showing very little plant matter, this type of coal has a less than ideal heating value. Bituminous coal is jet black, very dense, and brittle. This type of coal has high heating value.
The main point of this is that all of these fossil fuels are made of hydrocarbons. It may come as a surprise that these two elements, hydrogen and carbon, can create many, many different compounds with unique characteristics. What makes hydrocarbons valuable to our society is the stored energy stored within them. This energy is contained in the atomic bonds. The original source of this energy is all the solar energy the prehistoric organisms trapped in their bodies eons ago. How do we make use of this bond energy then? We burn them.
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Combustion is the process of breaking atomic bonds to release energy in the form of light and heat. Fossil fuels have many hydrocarbons, each with numerous bonds. When they undergo combustion, they release a great deal of heat. This is the main reason why natural gas and heating oils are used extensively in the world today. However, energy in the form of heat is by nature very chaotic and disorganized. Simply burning fossil fuels is wonderful for keeping the winter chill at bay, but setting oil on fire in your washing machine won't get your clothes clean. Likewise, we can't put petroleum directly out of the ground into our cars and expect them to operate. To make use of the resource of fossil fuels, humans have developed drilling, refining, and methods to harness fossil fuel energy.
Early oil explorers relied heavily on intuition and guesswork to find the precious 'black gold.' These daring entrepreneurs were known as 'wildcatters.' A fabled technique used by the wildcatters is the 'old hat.' They would basically toss their hat up in the air and wherever it landed, they drilled. When the wildcatters got lucky, and struck oil, it would typically gush up the drill pipe, hence, a gusher. Because gushers are a safety hazard and environmental concern, oil companies today contain them. After discovering an oil field, it is the task of the oil company's engineers and technicians to get it out. Not all oil fields turn out to be gushers and even the ones that are eventually loose pressure, leaving a lot of untapped fossil fuel resource in the reservoir. Even with modern extraction techniques, 100% of the oil in any given field is still not yet recoverable.
external image B1_01A6a.GIFOne thing an oil company does to facilitate the extraction process is setting up what is known as a 'Christmas tree,' a system of valves and pipes that regulate oil flow and pressure. Another system used in much smaller reservoirs not worth the expense of manning with technicians is the setup of a beam pump These are also known as 'nodding donkeys;' they extract oil from small oil pools that do not contain much resource. In large oil fields, techniques such as water and gas injection are employed to maximize return of the investment. By pumping water and gas into the wells, the pressure increases allowing oil to flow upwards once more Large oil fields can be found under the sea floor as well. To exploit these fields, vast oil drilling stations, which are marvels of modern engineering, tap into these underwater deposits and bring them to the surface.
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Although fossil fuels have been around long before humans even discovered fire, our prehistoric ancestors had no use for them. In the late 1800's, coal and gas were used as heat and light sources, steam locomotives as well. There were early automobiles too, but these vehicles were more of a novelty than a way of life. It wasn't until the 1940's did things change. Why the 1940's? The answer is that engineers and inventors had government support and extra incentive to develop fossil fuel technologies, war. World War II was the catalyst and not World War I because 'The War to End All Wars' was fought by men in trenches and mechanized warfare had only been developed late in the conflict. World War II had the German Blitzkrieg, or 'Lightning War.' This tactic utilized Shtuka dive bombers and Panzer tanks; German engineers enabled this, and was eventually countered by Allied technological advancements. From then on, usage and development of fossil fuels steadily rose.
The primary refining technique used to separate hydrocarbons and provide the ingredients for modern fuels is called fractional distillation. Hydrocarbons of different size and configuration usually have differences in boiling points that are large enough to use as a method of separation. By vaporizing them, they tend to float upwards until the hydrocarbons condense, which is where they are collected. Hydrocarbons as simple as butane and alcohols with few carbons are sorted along with more complex ones such as aromatics with 9 carbons. The fuels we commonly use today are a mixture of these hydrocarbons distilled from the petroleum extracted from the earth.
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Gasoline is a highly specialized fuel that contains hydrocarbons ranging from butane to C10. It is designed for the Otto-cycle engine, also known as spark ignition or 4-stroke engine. This engine as well as others will be described in more detail later on. Some characteristics of gasoline enable the following:1. Quick start at low temperatures
2. Fast acceleration
3. Low occurrence of stalling
4. Relatively quiet and low tendency to knock
5. Good combustion efficiency
The next classification of fuels is the distillate fuels. They are kerosene, turbo-jet fuel, diesel, and heating oil. Kerosene was the first petroleum fuel oil to be widely used; this was before electric lights and after the days of animal and vegetable oil. Kerosene has become less popular and is no longer produced in the quantities it once was. Countries with limited access to electricity and outdoors enthusiasts still have a use for this fuel.
Turbo-jet fuel was first developed in WWII for use in airplane engines. Because of constraints on petroleum products, namely gasoline for tanks and other ground vehicles, this fuel was designed to make use of compounds not vital to gasoline production whenever possible. The result was a highly volatile fuel that led to many accidents in handling. Modern aviation fuel is still more volatile than gasoline, though it has become much safer than it previously was.
Diesel fuel and domestic heating oil are similar in composition. Domestic heating oils are not widely used in the US, though they still have limited application in underdeveloped countries. Diesel fuels are used frequently in the world today; transport vehicles such as trains, boats, trucks, and busses use diesel fuel.
Fuel oils are mainly residuals from the fractional distillation process. They are more or less the leftovers from production of other fuels. They have been and are still used in power generation plants. Because of the low quality and high pollution content fuel oils are being used less often.
Of the fuels previously listed, gasoline, turbo-jet fuel, and diesel fuel were designed for usage in engines. A fairly good, simple definition of an engine is a device that converts chemical or heat energy into mechanical energy. Engines convert fossil fuel energy into a form that we can more readily use.
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The majority of engines in the world today are internal combustion engines. This type of engine is found in most machines and vehicles that run on fossil fuels. The first internal combustion engine was invented by Nicolaus August Otto. There are 4 general types of internal combustion engines that will be discussed here briefly. The first is the type designed by Mr. Otto himself, the Otto-cycle engine. These are the engines you typically find in cars. These are 4-stroke engines, named thus because it goes through 4 phases during operation: intake, compression, expansion, and exhaust. The parts of the engine directly involved in this cycle are the cylinder, the piston, the valves, and the spark plug.
external image 4stroke.gif

external image img013.gif· Intake-- Intake valve opesns allowing fuel/air mixture into the cylinder
· Compression-- The piston rises, reducing volume and increasing pressure
· Expansion (power stroke)-- Spark plug ignites, fuel expands pushing piston
· Exhaust-- Exhaust valve opens expelling spent fuel from cylinder
external image img015.gifThe second type of engine is known as a 2-stroke engine. These are usually placed in lawn mowers, outboard motors, and high performance recreational vehicles. There are two main differences between 4 and 2-stroke engines A 4-stroke engine causes two revolutions in one cycle whereas the 2-stroke only takes one revolution to complete its cycle. The other major difference between them is that 2-strokes require a gasoline/oil mixture as fuel. This is because the cylinder must be kept completely bathed in lubricants to prevent damage. Due to these attributes, these engines are much more compact and can generate higher revolutions per minutes and more acceleration. The problem with this design is that it is not at all fuel efficient and burning motor oil causes a lot of pollution.
Diesel engines, as you might know, require no spark plugs in the combustion process. Otherwise, the design of the diesel engine is not much different than an Otto-cycle engine. Instead of spark plugs, the diesel engine relies on compression and the heating of air in the fuel mixture to cause ignition. To achieve this, diesel fuel has a lower boiling point and does not require much heat. Diesel fuel is cheaper to make than gasoline, though its high level of pollutants require it to undergo further filtration; this drives the fuel price up.
The last type of conventional engine discussed here is the wankel rotary combustion engine, named after its inventor, Felix Wankel. Out of the engines discussed, this one is the most 'revolutionary' (excuse the pun). The wankel engine does not use pistons, instead it uses a rotor. The rotor spins and drives the shaft by expanding fuel in the housing on the sides of the rotor. The results of this engine type are as follows:
· Light weight and compact
· Smooth: no reciprocating motion
· Extended power stroke rotation: 270 degrees vs. 180 degrees of a piston
· Fewer moving parts
· Cooler combustion means fewer oxides of nitrogen
The wankel engine was used in the Mazda motorcars RX series of cars. For all the advantages of this engine, it had one major drawback, it was extremely inefficient in fuel consumption. The oil crisis in 1973 caused this engine to loose support and funding for further development to improve consumption. Currently the RX series of Mazda cars is no longer in production, however Mazda has made a RX-01 concept car. Wankel rotary engines can also be found in porches and other powerful sports cars.
Aviation fuel, the turbo-jet fuel, is used by both jet and propeller aircraft today. Prop engines are designed similar to the 4-stroke engines of cars, though the demands on these two varieties of engines are quite different. external image layout.gifTo accommodate this, prop engines are much larger and have higher power output. The distillate fuel they use is ideal for this purpose. With the inception of jet propulsion the fuels used did not change all that much. Even though it may seem that the jet engine is very different, it is still considered to be an internal combustion engine. The main components of a jet engine are the compressor, combustion chamber, and the turbine. Air flows into the compressor where it is pressurized and forced into the combustion chamber There, inside the chamber, fuel is constantly flowing in, and ignited causing an expansion of the fuel The turbine's purpose is to provide enough energy from the expelled gasses to the compressor in order to operate at peak performance. Jet engine technology has advanced greatly and there are many different types of them. Just to list a few, there are turbojet, turbofan, turboprop, turboshaft, and ramjet designs. Each have specialized uses, mostly in aviation technology.

Fossil fuels are excellent sources of energy for out transportation needs; however they are also the primary source of electrical energy in the world today. Coal power plants account for at least 60% of our national energy and 52% of the world's demand. We, as a world, burn approximately 1.9 billion tons of coal a year to generate electricity.
How we get electrical energy from coal is by means of coal power plants. These power plants first combust the coal in large furnaces creating tremendous amounts of heat. This heat is used to evaporate water in boilers so they convert to steam. The steam expands, causing pressure to increase in the boiler. A steam turbine is placed at the exit of the boiler where it converts energy from the moving steam into mechanical energy. The rotation of this turbine is used to spin a magnet inside a power generator. This generator is a large electromagnet that encases the spinning magnet. Instead of putting electricity into the electromagnet to cause the coil to magnetize, electrons are captured from the spinning magnet and collected. The electrons are then sent to the national power grid where they are distributed as needed.
Air particles are deadly. The byproducts that form from the burning of fossil fuels are very dangerous. These small particles can exist in the air for indefinate periods of time, up to several weeks and can travel for miles. The particles, sometimes smaller than 10 microns in diameter, can reach deep within the lungs. Particles that are smaller than this can enter the blood stream, irritating the lungs and carry with them toxic substances such as heavy metals and pollutants. Over a lifetime of continued exposure, a person's ability to transfer oxygen and rid pollutants is impeded. Those affected could become afflicted with fatal asthma attacks and other serious lung conditions. the World Resources Institute reports that between the years of 2000 and 2020, 8 million deaths worldwide could possibly occur without changing present conditions. In 1990 alone, respiratory diseases were a leading cause of disabilities and illnesses worldwide. This is a global problem and requires a global solution. Because the contamination is growing at an exponential rate, minor reductions now will greatly reduce the number of lives lost in the future.With the United States importing 55% of its oil, oil spills are a serious problem. The Exxon Valdez oil spill awakened the nation as we saw its effects on television. To this day there still exsists measurable differences in the environment. Some species have not been able to recover.
Description Of Injury
Status Of Recovery
Comments / Discussion
Oil Spill Morality (est.)
Measured Decline
Sublethal / Chronic Effects
Current Population Status
Continuing Effects
Harbor Seals
Many seals were directly oiled. There was a greater decline in population in oiled vs. unoiled areas in 1989 and 1990. Population was in decline prior to the spill and recovery has still not begun possibly due to lack of preferred diet. Current population decline is 6% per year.
Killer Whales
13 adult whales of the AB pod were missing and presumed dead in 1990 and no young were produced in 1990 or 1991. The pod gained 4 members in the following two years but since then there have been more losses than births. Some experts think that the loss of 13 whales is not related to the spill.
Sea Lions
Continuing Decline
Several sea lions were observed with oiled pelts and oil residues were found in some tissues. It was not possible to determine population effects or cause of death of carcasses recovered. Sea lions were already in decline prior to the spill.
Sea Otters
(3,500 to 5,500)
Survival differences between oiled and unoiled areas have been noticed since the spill. Sea Otters feed in the lower intertidal zones and may still be effected by hydrocarbons in the environment.
River Otter
(total unknown)
Exposure to hydrocarbons and possible sublethal effects were determined, but no effects were established on population. In 1991 studies showed that exposure to hydrocarbons still remained probably from exposure through diet.
Bald Eagle
(200 or more)
Productivity was disrupted in 1989 but returned to normal in 1990. Exposure to hydrocarbons was found in 1989 and it is assumed that the source, based on visual observation, was from eating oiled carcasses.
Black Oyster-
(120 to 150 adults)
Differences in egg sizes between oiled and unoiled areas were found in 1989. Populations declined more in oiled areas during 1989, 1990, 1991, 1992. Possibly due to exposure to hydrocarbons through diet.
Common Murres
(170,000 to
Measurable impacts on population were recorded in 1989, 1990, 1991, and 1992. Breeding is still reduced in some areas of the Gulf Of Alaska.
Harlequin Ducks
(approx. 1,000)
Population declines lasted through 1992 partially due to reproductive failure. Currently studies are focusing on differences on winter survival rates between western and eastern Prince William Sound
Marbled Murrelets
(8,000 to 12,000)
Continuing Decline
Marbled murrelets experienced a 7% population decline due to the spill. Measurable population decline was also observed before the spill and continuing today.
Pigeon Guillemonts
Yes (1,500 to 3,000)
Populations were in decline before the spill. The spill claimed between 10 and 15 percent of the population throughout the region. Hydrocarbon contamination is assumed based on the finding of hydrocarbons on the exterior of their eggs.
Pacific Herring
To Eggs & Larva
See Comments
Measurable egg counts between oiled and unoiled areas were found in 1989 and 1990. In 1989, 1990, 1991 lethal and subleathal effects on eggs and larvae were found. In 1993 the population crashed due to a viral disease and fungus. Commercial fishing seasons were closed for four years between 1993 and 1997.
Pink Salmon
to eggs
See Comments
Severe effects were inflicted on fry in 1989 and 1990 and continued to be high in 1991 and 1992. Fishing seasons were closed in 1989. Wide swings in returns have been documented but are more likely due to natural causes. The SEA ecosystem project is currently studying these swings.
Description of Injury
Commercial Fishing
During 1989 emergency fishing closures were ordered in Prince William Sound, Cook Inlet, Kodiak and the Alaska Peninsula. This affected salmon, herring, crab, shrimp, rockfish, and sablefish. The 1989 closures resulted in over-escapement in the Kenai River and in the Red Lake system. Limited closures were also in effect in 1990.
Low adult sockeye returns in 1994 were a result of the over-escapement from Kenai River. Future fishing seasons may need to be closed to balance out the problem.
Recreation & Tourism
Some commercial recreation and tourism businesses were injured by the reduction in visitor spending as a result of the spill. Non-commercial recreation also decreased in some parts of the spill area. The quality of recreational experiences also decreased due to crowding, residual oil, and fewer fish and wildlife
Recreational users are benefiting from restoration projects in several ways. Habitat protection opens up land previously off limits to campers, hunters, sport fishers, and wildlife viewers while at the same time protecting the health of fish, bird and marine populations. In 1996 a 220-acre Cook Inlet bluff parcel was purchased and will be turned into a state-run campground and recreational facility. Money from the Exxon Settlement is also being used to build campgrounds, cabins, trails, bridges, buoys, food cages, fire rings, docks and interpretive signs.

Natural Gas
Natural gas accounts for 24% of the energy in the United States. Domestic production of natural gas peaked in 1973; this is because we do not import due to safety problems. Consumption of natural gas is actually flat as oppsed to increasing usage of coal and oil.
Petroleum / Natural Gas will run out in the next 50 years. 97% of fossil fuel reserves are coal. 20% of the world's coal supply is located in the United States.
    • Energy yield depends on how much carbon is contained in the coal. Two types dominate US reserves. Anthracite is 95% carbon and is approximately 300 million years old. Lignite is 25% carbon is nearly 150 million years old.
    • Deposits are around 300 feet below the surface and typically 2-8 feet thick.
    • Coal production has increased since 1970.
    • At current usage, the supply will last 1500 years. However at a 5% growth rate the supply will last only 86 years. We can expect even greater usage as other fossil fuels become scarce.
Shale Oil
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Shale oil deposits in the US are found in southwestern Wyoming, eastern Utah, and western Colorado. Oil shale contains kerogen which, when burned, can be converted into fuel products. The amount of shale oil deposits are significantly greater than the amount of US petroleum deposits by a factor of ten. However, economic mining requires a yield of 25 gallons of oil per ton of shale. Only 30% of the known deposits meet this criteria. Of that 30%, only 15% is recoverable under present conditions. The refinement of shale is very difficult and requires large amounts of water. The bottom line is that shale oil is not economically viable at this point.

week 6

external image 220px-Top_of_Atmosphere.jpgexternal image magnify-clip.pngBlue light is scattered more than other wavelengths by the gases in the atmosphere, giving the Earth a blue halo when seen from space.

external image 220px-Sunset_from_the_ISS.JPGexternal image magnify-clip.png Limb view, of the Earth’s atmosphere. Colours roughly denote the layers of the atmosphere.

external image 180px-Atmosphere_gas_proportions.svg.pngexternal image magnify-clip.png Composition of Earth's atmosphere. The lower pie represents the trace gases which together compose 0.039% of the atmosphere. Values normalized for illustration. The numbers are from a variety of years (mainly 1987, with CO2 and methane from 2009) and do not represent any single source.

external image 220px-Atmospheric_Water_Vapor_Mean.2005.030.jpgexternal image magnify-clip.png Mean atmospheric water vapor

Principal layers

external image 170px-Atmosphere_layers-en.svg.pngexternal image magnify-clip.png Layers of the atmosphere (not to scale)
Earth's atmosphere can be divided into five main layers. These layers are mainly determined by whether temperature increases or decreases with altitude. From highest to lowest, these layers are:
ExosphereThe outermost layer of Earth's atmosphere extends from the exobase upward. Here the particles are so far apart that they can travel hundreds of km without colliding with one another. Since the particles rarely collide, the atmosphere no longer behaves like a fluid. These free-moving particles follow ballistic trajectories and may migrate into and out of the magnetosphere or the solar wind. The exosphere is mainly composed of hydrogen and helium.ThermosphereTemperature increases with height in the thermosphere from the mesopause up to the thermopause, then is constant with height. The temperature of this layer can rise to 1,500 °C (2,730 °F), though the gas molecules are so far apart that temperature in the usual sense is not well defined. The International Space Station orbits in this layer, between 320 and 380 km (200 and 240 mi). The top of the thermosphere is the bottom of the exosphere, called the exobase. Its height varies with solar activity and ranges from about 350–800 km (220–500 mi; 1,100,000–2,600,000 ft).MesosphereThe mesosphere extends from the stratopause to 80–85 km (50–53 mi; 260,000–280,000 ft). It is the layer where most meteors burn up upon entering the atmosphere. Temperature decreases with height in the mesosphere. The mesopause, the temperature minimum that marks the top of the mesosphere, is the coldest place on Earth and has an average temperature around −85 °C (−121.0 °F; 188.1 K)[3]. Due to the cold temperature of the mesophere, water vapor is frozen, forming ice clouds (or Noctilucent clouds). A type of lightning referred to as either sprites or ELVES, form many miles above thunderclouds in the trophosphere.StratosphereThe stratosphere extends from the tropopause to about 51 km (32 mi; 170,000 ft). Temperature increases with height, which restricts turbulence and mixing. The stratopause, which is the boundary between the stratosphere and mesosphere, typically is at 50 to 55 km (31 to 34 mi; 160,000 to 180,000 ft). The pressure here is 1/1000th sea level.TroposphereThe troposphere begins at the surface and extends to between 7 km (23,000 ft) at the poles and 17 km (56,000 ft) at the equator, with some variation due to weather. The troposphere is mostly heated by transfer of energy from the surface, so on average the lowest part of the troposphere is warmest and temperature decreases with altitude. This promotes vertical mixing (hence the origin of its name in the Greek word "τροπή", trope, meaning turn or overturn). The troposphere contains roughly 80%[citation needed] of the mass of the atmosphere. The tropopause is the boundary between the troposphere and stratosphere.

Other layers

Within the five principal layers determined by temperature are several layers determined by other properties.
  • The ozone layer is contained within the stratosphere. In this layer ozone concentrations are about 2 to 8 parts per million, which is much higher than in the lower atmosphere but still very small compared to the main components of the atmosphere. It is mainly located in the lower portion of the stratosphere from about 15–35 km (9.3–22 mi; 49,000–110,000 ft), though the thickness varies seasonally and geographically. About 90% of the ozone in our atmosphere is contained in the stratosphere.
  • The ionosphere, the part of the atmosphere that is ionized by solar radiation, stretches from 50 to 1,000 km (31 to 620 mi; 160,000 to 3,300,000 ft) and typically overlaps both the exosphere and the thermosphere. It forms the inner edge of the magnetosphere. It has practical importance because it influences, for example, radio propagation on the Earth. It is responsible for auroras.
  • The homosphere and heterosphere are defined by whether the atmospheric gases are well mixed. In the homosphere the chemical composition of the atmosphere does not depend on molecular weight because the gases are mixed by turbulence.[4] The homosphere includes the troposphere, stratosphere, and mesosphere. Above the turbopause at about 100 km (62 mi; 330,000 ft) (essentially corresponding to the mesopause), the composition varies with altitude. This is because the distance that particles can move without colliding with one another is large compared with the size of motions that cause mixing. This allows the gases to stratify by molecular weight, with the heavier ones such as oxygen and nitrogen present only near the bottom of the heterosphere. The upper part of the heterosphere is composed almost completely of hydrogen, the lightest element.
  • The planetary boundary layer is the part of the troposphere that is nearest the Earth's surface and is directly affected by it, mainly through turbulent diffusion. During the day the planetary boundary layer usually is well-mixed, while at night it becomes stably stratified with weak or intermittent mixing. The depth of the planetary boundary layer ranges from as little as about 100 m on clear, calm nights to 3000 m or more during the afternoon in dry regions.
The average temperature of the atmosphere at the surface of Earth is 14 °C (57 °F; 287 K)[5] or 15 °C (59 °F; 288 K)[6], depending on the reference.[7] [8][9]

external image 220px-Sauerstoffgehalt-1000mj2.pngexternal image magnify-clip.png Oxygen content of the atmosphere over the last billion years


Main article: Atmospheric circulationexternal image 220px-AtmosphCirc2.pngexternal image magnify-clip.png An idealised view of three large circulation cells.
Atmospheric circulation is the large-scale movement of air, and the means (with ocean circulation) by which heat is distributed around the Earth. The large-scale structure of the atmospheric circulation varies from year to year, but the basic structure remains fairly constant as it is determined by the Earth's rotation rate and the difference in solar radiation between the equator and poles.

Evolution of Earth's atmosphere

See also: History of Earth, Gaia hypothesis, and Paleoclimatology

Second atmosphere

Water related sediments have been found dating from as early as 3.8 billion years ago.[12] About 3.4 billion years ago, nitrogen was the major part of the then stable "second atmosphere." An influence of life has to be taken into account rather soon in the history of the atmosphere, since hints of early life forms are to be found as early as 3.5 billion years ago.[13] The fact that this is not perfectly in line with the - compared to today 30% lower - solar radiance of the early Sun has been described as the "Faint young Sun paradox".
The geological record however shows a continually relatively warm surface during the complete early temperature record of the Earth with the exception of one cold glacial phase about 2.4 billion years ago. In the late Archaean era an oxygen-containing atmosphere began to develop, apparently from photosynthesizing algae which have been found as stromatolite fossils from 2.7 billion years ago. The early basic carbon isotopy (isotope ratio proportions) is very much in line with what is found today,[14] suggesting that the fundamental features of the carbon cycle were established as early as 4 billion years ago.

Third atmosphere

external image magnify-clip.png Oxygen content of the atmosphere over the last billion years
The accretion of continents about 3.5 billion years ago[15] added plate tectonics, constantly rearranging the continents and also shaping long-term climate evolution by allowing the transfer of carbon dioxide to large land-based carbonate storages. Free oxygen did not exist until about 1.7 billion years ago and this can be seen with the development of the red beds and the end of the banded iron formations. This signifies a shift from a reducing atmosphere to an oxidising atmosphere. O2 showed major ups and downs until reaching a steady state of more than 15%.[16] The following time span was the Phanerozoic era, during which oxygen-breathing metazoan life forms began to appear.
Currently, anthropogenic greenhouse gases are increasing in the atmosphere. According to the Intergovernmental Panel on Climate Change, this increase is the main cause of global warming.[17]

Air pollution

Main article: Air pollution
Air pollution is the human introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to organisms into the atmosphere.[18] Stratospheric ozone depletion is believed to be caused by air pollution (chiefly from chlorofluorocarbons).[citation needed]

The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night. Dry air contains roughly (by volume) 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.038% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1%.
The atmosphere has a mass of about 5 × 1018 kg, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. An altitude of 120 km (75 mi) is where atmospheric effects become noticeable during atmospheric reentry of spacecraft. The Kármán line, at 100 km (62 mi), also is often regarded as the boundary between atmosphere and outer space.
Air is mainly composed of nitrogen, oxygen, and argon, which together constitute the major gases of the atmosphere. The remaining gases are often referred to as trace gases,[1] among which are the greenhouse gases such as water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Filtered air includes trace amounts of many other chemical compounds. Many natural substances may be present in tiny amounts in an unfiltered air sample, including dust, pollen and spores, sea spray, volcanic ash, and meteoroids. Various industrial pollutants also may be present, such as chlorine (elementary or in compounds), fluorine compounds, elemental mercury, and sulfur compounds such as sulfur dioxide [SO2].
Composition of dry atmosphere, by volume[2]|||| ppmv: parts per million by volume (note: volume fraction is equal to mole fraction for ideal gas only, see Gas Volume) ||
Nitrogen (N2)
780,840 ppmv (78.084%)
Oxygen (O2)
209,460 ppmv (20.946%)
Argon (Ar)
9,340 ppmv (0.9340%)
Carbon dioxide (CO2)
390 ppmv (0.0390%)
Neon (Ne)
18.18 ppmv (0.001818%)
Helium (He)
5.24 ppmv (0.000524%)
Methane (CH4)
1.79 ppmv (0.000179%)
Krypton (Kr)
1.14 ppmv (0.000114%)
Hydrogen (H2)
0.55 ppmv (0.000055%)
Nitrous oxide (N2O)
0.3 ppmv (0.00003%)
Carbon monoxide (CO)
0.1 ppmv (0.00001%)
Xenon (Xe)
0.09 ppmv (9 × 10−6%)
Ozone (O3)
0.0 to 0.07 ppmv (0% to 7 × 10−6%)
Nitrogen dioxide (NO2)
0.02 ppmv (2 × 10−6%)
Iodine (I)
0.01 ppmv (1 × 10−6%)
Ammonia (NH3)
Not included in above dry atmosphere:
Water vapor (H2O)
~0.40% over full atmosphere, typically 1%-4% at surface


Well, as inhabitants of planet Earth, we are part of it. The Earth formed when all the other planets did. The whole system was once one big disk of gas and dust, with a baby sun in the center. Gradually, the matter coalesced to form the planets. One of them struck the Earth very early on, and the debris from it and the Earth formed a ring, which became the Moon. Comets crashed on the Earth's surface and grazed its atmosphere, dropping all the water we have today, making life itself possible. The Sun drives the chemical reactions here, including those that make life possible. But it can also threaten humans, with solar flares. Another danger from space is an asteroid strike.

Our Solar System: One in a Hundred Billion?

Planet Earth is part of a vast space neighborhood called the solar system. Our solar system is an amazing place. It’s even more amazing that at least 70 other solar systems have been discovered. And there could be lots more. Scientists estimate there could be hundreds of billions of solar systems in our Milky Way galaxy.
Milky Way
Milky Way

Our solar system is one of many groups of planets (planetary systems) that call the Milky Way Galaxy home.
We may never know the actual number, but all solar systems work the same way. Planets and other space objects revolve around a star. In our system, the star is the sun. Eight major planets and their moons, three “dwarf” planets, and countless asteroids, meteoroids, comets, and other objects whiz around it. Each object travels in its own egg-shaped orbit. The shape is called an ellipse.

It Began with a Bang

About 15-20 billion years ago, there was an enormous explosion called the Big Bang. Whirling clouds of dust and gas filled the Universe. Over time, gravity made some clouds start to clump together. Big clumps formed galaxies. Smaller clumps became stars.
Then, about 4.5 billion years ago, the clouds that formed our solar system spun so fast they formed a disk. The center of the disk became so hot it dropped out. That center became the sun. The dust and gas that didn’t get sucked into the center stuck together in clumps. These clumps became planets. Our solar system was born.

The Big Star of Our Show


The eight planets of our solar system revolve around a large star called the sun.
The sun is the center because it’s HUGE. More than one million Earths could fit inside it. It contains more than 99.8% of all the mass in the solar system. Its size gives it the gravity it needs to hold the solar system together. The sun’s gravity pulls the objects down while they keep trying to move away. It’s a never-ending tug-of-war that keeps the planets in their orbits instead of flying off into space.

Let’s Take a Spin

It takes Earth 366.6 days to make one revolution around the sun. That’s about a year. But a year on Earth is not the same as a year on another planet. The length of a planet’s “year” depends on its size and its distance from the sun. Smaller planets travel faster. Planets far from the sun have a longer trip than those close in.
While the planets spin around the sun, each one also spins around its own axis. The time it takes a planet to make one complete turn, or rotation, is called a day. A day on Earth is 23 hours and 56 minutes. Days on other planets are longer or shorter.

Mars Rocks. Jupiter Is a Gas.

Terrestrial Planets
Terrestrial Planets

Earth is one of four planets in our solar system that have solid, rocky surfaces. These planets are called terrestrial planets.
©Lunar and Planetary Institute
Mercury, Venus, Earth and Mars are called the “terrestrial” planets. Terrestrial comes from the Latin word terra, which means “earth.” All these planets have solid, rocky surfaces. They’re also called the “inner” planets.
Jupiter, Saturn, Uranus and Neptune are called the “gas giants.” They do not have solid surfaces. They’re made of dense clouds of gases. These planets are also called the “outer” planets.

Sorry, Pluto!

Pluto was once the ninth planet in our solar system. But in 2006, scientists kicked it out of the lineup. Why? They had come up with new rules about what makes a “real” planet. Pluto just didn’t measure up.
The rules are:
  • A planet must be shaped like a sphere.
  • It must orbit the sun.
  • It must have enough gravity to keep it from being pulled into another planet’s orbit.
  • It must have enough gravity to pull in rocks and other space “junk” orbiting around it.

Pluto is one of three known dwarf planets in our solar system.
Pluto is shaped kind of like a potato. It has a weird orbit that sometimes crosses into Neptune’s. And it has a lot of debris orbiting around it. So scientists reclassified Pluto as a “dwarf” planet, along with Ceres and Eris.



There are more than hundreds of thousands of asteroids in our solar system and most of them are found within the main asteroid belt.
What else orbits the sun? Asteroids are loose chunks of rock that scientists think may be left over from the formation of the solar system. They may be pieces of a planet that broke apart, or just a small clump that never merged with bigger ones. Most of the asteroids orbit the sun in a region between Mars and Jupiter known as the Asteroid Belt.


Meteoroids are smaller than asteroids. They may be pieces of planets that flew off during a space collision. They could be pieces of dust left behind in the trail of a comet. Or they could be pieces of asteroids that broke apart.
Meteoroids burn up when they enter the Earth’s atmosphere. The bright trails they leave behind them are called meteors, or “shooting stars.” Larger pieces that don’t burn up completely in the atmosphere and make it to the surface of the Earth are called “meteorites.”

Comet McNaught was the brightest comet to shoot across the sky in the Southern hemisphere in 40 years.
©Jens Hackmann


Comets are sometimes called “dirty snowballs.” They’re made of icy material mixed with rocks and dust. Scientists think that comets, like asteroids, are left over from when the solar system formed.

Watchers and Wanderers

The earliest astronomers studied the sun, stars, and planets as the complete universe. They believed Earth was the center of everything. They noticed that stars did not change positions except to move as one across the sky. They noticed other star-like objects, too. These objects seemed to wander among the stars. So they named the objects “planets,” after the Greek word for “wanderers.”
In the early 1500’s, astronomer Nicholas Copernicus had an idea that made people very angry. He said that the sun, not Earth, was the center of the solar system. People didn’t like the idea one bit. How could the sun be more important than Earth? Copernicus’s theories were unpopular, but he started modern astronomy. Later, Galileo Galilei was among the first astronomers to observe the planets with a telescope.

Twinkle, Twinkle, Little . . . Planet?

Today powerful telescopes let us see things early astronomers could only dream of. Spacecraft and satellites send back astonishing images from the outer edges of the solar system. Still, you can study the planets with your own eyes. But how can you tell if you’re looking at a star or a planet?

Astronomers use powerful telescopes to study the sun, stars, moons, planets, and other bodies in space.
©Greg Piepol
The sun is our closest star. Its light is close enough to brighten and warm our world. But light from other stars comes from very, very far away. By the time it reaches us, it’s just a tiny pinpoint. As we look through the atmosphere at that point of light, it gets shifted around by all the “stuff” going on in the atmosphere. That’s what makes it twinkle. Planets are closer. Their light isn’t so “pointy.” It doesn’t get shifted around as much. So if you watch a star for a while and it doesn’t twinkle, it just may be a planet!

week 8

Human and natural activity can affect the earth and its environment in many different ways here are some of them:
· Plastic is not decomposable and making plastics and other decomposable wastes causes landfill which can cause pollution of the local environment such as contamination of groundwater.
· Radioactive waste produced by nuclear power stations can be dangerous in cases of radioactive contamination of a human body through ingestion, inhalation, absorption, or injection. Sea-based burial has caused damage such as it could leak and cause widespread damage. Dumping of radioactive waste from ships has also caused contamination of islands in the Pacific.
· Deforestation, the destroying of forests, results from the removal of trees without replacing them. Deforestation could result in the depletion of the renewable resource wood and various organisms' habitats. The photograph to the right is a NASA satellite observation of deforestation near Rio Branco in Brazil. About half of the mature tropical forests, between 750 to 800 million hectares of the original 1.5 to 1.6 billion hectares that once covered the planet have fallen. Throughout most of history, humans have considered forest clearing as necessary for most activities.
· Overfishing is another activity that could cause the depletion of a natural resource. Most of the problems associated with overfishing have been caused in the last 50 years by the rapid advances in fishing technology. Overfishing can occur in any body of water from a pond to the oceans. Deliberately underfishing to increase long term fish stocks has been proposed as a way fisherman can maximize their yields in the long run. · Large amounts of greenhouse gases being produced, such as carbon dioxide, are causing our planet to get warmer. These gases allow sunlight to enter the atmosphere freely. When sunlight strikes the Earth's surface, some of it is reflected back towards space as infrared radiation but greenhouse gases absorb this infrared radiation and trap the heat in the atmosphere causing global warming. Global warming is melting the ice caps causing the ocean level of our planet to increase, this causes flooding in many different areas of our planet.
The human activities are comprised of many things which can destroy as well as endanger the environment and nature surrounding us. They are: coal mining (fossil extraction), factories, vehicles etc. They can pollute our environment and can destroy the nature and the animals. Those activities give a risk to them.Human activities involve dangerous chemicals such as c02s or involve smoke that ruins or atmoshpere and polutes our air. Our atmosphere protects us from dangerous radiation.
Human impact on the natural environment
Natural environment is of crucial importance for social and economic life. We use the living world as
  • a resource for food supply
  • an energy source
  • a source for recreation
  • a major source of medicines
  • natural resources for industrial products
In this respect the diversity of nature not only offers man a vast power of choice for his current needs and desires. It also enhances the role of nature as a source of solutions for the future needs and challenges of mankind.
State of ecosystems, habitats and species
In the past, human interaction with nature, although often having a disruptive effect on nature, often also enriched the quality and variety of the living world and its habitats - e.g. through the creation of artificial landscapes and soil cultivation by local farmers.
Today, however, human pressure on natural environments is greater than before in terms of magnitude and efficiency in disrupting nature and natural landscapes, most notably:
  • intensive agriculture replacing traditional farming; this combined with the subsidies of industrial farming has had an enormous effect on western rural landscapes and continues to be a threat.
  • mass tourism affecting mountains and coasts.
  • the policies pursued in the industry, transport and energy sectors having a direct and damaging impact on the coasts, major rivers (dam construction and associated canal building) and mountain landscapes (main road networks).
  • the strong focus of forestry management on economic targets primarily causes the decline in biodiversity, soil erosion and other related effects.
The clearest manifestations of the degradation of the natural environment are:
  • Reduction and fragmentation of habitats and landscapes

The expansion of humans activities into the natural environment, manifested by urbanisation, recreation, industrialisation, and agriculture, results in increasing uniformity in landscapes and consequential reduction, disappearance, fragmentation or isolation of habitats and landscapes.
It is evident that the increasing exploitation of land for human use greatly reduces the area of each wildlife habitat as well as the total area surface throughout Europe. The consequences are:
    • A decreased species diversity, due to reduced habitable surface area which corresponds to a reduced "species carrying capacity".
    • The reduction of the size of habitats also reduces the genetic diversity of the species living there. Smaller habitats can only accommodate smaller populations, this results in an impoverished gene pool.
    • The reduction of genetic resources of a species diminishes its flexibility and evolutionary adaptability to changing situations. This has significant negative impacts on its survival.
The conditions under which the reduction of habitats often occur prevent living organisms making use of their normal ways to flee their threatened habitat. Those escape routes include migration to other habitats, adaption to the changing environment, or genetic interchange with populations in nearby habitats. Of particular concern is:
    • The abrupt nature of human intervention; human projects are planned and implemented on a much shorter time scale than natural processes;
    • Furthermore human intervention, such as the construction of buildings, motorways or railways results in the fragmentation of habitats, which strongly limits the possibility for contact or migration among them;
    • In extreme cases even the smallest, narrowest connections between habitats are broken off. Such isolation is catastrophic for life in the habitat fragments.
  • Loss of Species of Fauna and Flora

Although relatively few species of Europe's fauna and flora have actually become totally extinct during this century, the continent's biodiversity is affected by decreasing species numbers and the loss of habitats in many regions. Approximately 30 % of the vertebrates and 20 % of the higher plants are classified as "threatened". Threats are directly linked to the loss of habitats due to destruction, modification and fragmentation of ecosystems as well as from overuse of pesticides and herbicides, intensive farming methods, hunting and general human disturbance. The overall deterioration of Europe's air and water quality add to the detrimental influence.----
Europe's natural environment is inextricably linked with agriculture and forestry. Since agriculture traditionally depends on sound environmental conditions, farmers have a special interest in the maintenance of natural resources and for centuries maintained a mosaic of landscapes which protected and enriched the natural environment.
As a result of needs for food production since the 1940s, policies have encouraged increased pro- duction through a variety of mechanisms, including price support, other subsidies and support for research and development. The success achieved in agricultural production has however entailed increased impact on the environment.
Modern agriculture is responsible for the loss of much wildlife and their habitats in Europe, through reduction and fragmentation of habitats and wildlife populations. The drainage of wetlands, the destruction of hedgerows and the intensive use of fertilizers and pesticides can all pose a threat to wildlife. Highly specialised monoculture are causing significant loss in species abundance and diversity. On the other hand increased production per hectare in intensive areas, raising of livestock volume, and lower prices for agricultural products also caused marginalization of agricultural land, changing the diversity of European landscapes into the direction of two main types: Intensive Agriculture and Abandoned land.

Abandonment can be positive for nature, but this is not necessarily so. Land abandonment increases the risk of fire in the Mediterranean Region, causes a decline of small-scale landscape diversity and can also cause decrease in species diversity.
All energy types have potential impacts on the natural environment to varying degrees at all stages of use, from extraction through processing to end use. Generating energy from any source involves making the choices between impacts and how far those impacts can be tolerated at the local and global scale. This is especially of importance for nuclear power, where there are significant risks of radioactive pollution such as at Chernobyl.
Shell Oil Company and IUCN have jointly drafted environmental regulations for oil-exploitation in Arctic areas of Siberia. Other oil companies are aware of this and use these environmental regula- tions voluntarily for developing oil fields.
Into the future the sustainability of the natural environment will be improved as trends away from damaging energy uses and extractive methods reduce and whilst real cost market forces and the polluter pays principle take effect.

The principle of the fisheries sector is towards sustainable catches of wild aquatic fauna. The principle environmental impact associated with fisheries activities is the unsustainable har- vesting of fish stocks and shellfish and has consequences for the ecological balance of the aquatic environment. The sector is in a state of "crisis", with over capacity of the fleet, overexploitation of stocks, debt, and marketing problems.
Growing aquaculture industry may increase water pollution in western Europe, and is appearing to be a rising trend in the Mediterranean and Central/East Europe.
Fishing activities have an impact on cetaceans and there is concern that large numbers of dolphins, and even the globally endangered Monk seal, are being killed.

Compared to other landuses, forest management has the longest tradition in following sustainable principles due to which over 30% of Europe is still covered with trees. Without such an organised approach, forests are likely to have already disappeared from Europe's lowlands. However, as an economic sector, forestry has also impacted severely on the naturalness of Europe's forests: soils have been drained, pesticides and fertilizers applied, and exotic species planted. In many areas monocultures have replaced the original diverse forest composition. Monocultures are extremely sensitive to insect infestations, fires or wind, and so can lead to financial losses as well as biological decline. The inadequate afforestation practices characterize new trends in impacting on the sustainability of the natural environment.

Almost all forms of industry have an impact on the natural environment and its sustainability. The impact varies at different stages in the life cycle of a product, depending upon the raw materials used through to the final end use of the product for waste residue, re-use or recycling. Industrial accidents and war damage to industrial plants can also endanger the natural environment.

Tourism and Recreation
Tourism and recreation impact in various ways on the natural environment. On the one hand, natural areas form the very basis of many touristic attractions by highlighting scenic value or exceptional encounters with fauna and flora. However, some forms of tourism can be extremely detrimental to ecologically sensitive areas, resulting in habitat degeneration or destruction, in the disturbance or hunting even rare or threatened species. The pressure from short holiday seasons and specific, sometimes small, locations of touristic interest result in conflicting land-uses, such as in the Alpine regions, at Mediterranean beaches and along many banks of inland waters.

Transport and Infrastructure
Transport is perhaps the major contributor to pollution in the world today, particularly global envi- ronmental issues such as the greenhouse effect. The key impacts of transportation include frag- mentation of habitats and species and genetic populations, disruption of migration and traffic mortalities to wildlife. Since the 1970s transport has become a major consumer of non-renewable resources, 80% of oil consumption coming from road transport.


external image 220px-Soil_Erosion_With_Roots.JPGexternal image magnify-clip.png Soil erosion exposing roots
The rate of erosion depends on many factors. Climatic factors include the amount and intensity of precipitation, the average temperature, as well as the typical temperature range, and seasonality, the wind speed, storm frequency. The geologic factors include the sediment or rock type, its porosity and permeability, the slope (gradient) of the land, and whether the rocks are tilted, faulted, folded, or weathered. The biological factors include ground cover from vegetation or lack thereof, the type of organisms inhabiting the area, and the land use.
In general, given similar vegetation and ecosystems, areas with high-intensity precipitation, more frequent rainfall, more wind, or more storms are expected to have more erosion. Sediment with high sand or silt contents and areas with steep slopes erode more easily, as do areas with highly fractured or weathered rock. Porosity and permeability of the sediment or rock affect the speed with which the water can percolate into the ground. If the water moves underground, less runoff is generated, reducing the amount of surface erosion. Sediments containing more clay tend to erode less than those with sand or silt. Here, however, the impact of atmospheric sodium on erodibility of clay should be considered.[3]
The factor that is most subject to change is the amount and type of ground cover. In an undisturbed forest, the mineral soil is protected by a litter layer and an organic layer. These two layers protect the soil by absorbing the impact of rain drops. These layers and the underlying soil in a forest are porous and highly permeable to rainfall. Typically, only the most severe rainfall and large hailstorm events will lead to overland flow in a forest. If the trees are removed by fire or logging, infiltration rates become high and erosion low to the degree the forest floor remains intact. Severe fires can lead to significantly increased erosion if followed by heavy rainfall. In the case of construction or road building, when the litter layer is removed or compacted, the susceptibility of the soil to erosion is greatly increased.
Roads are especially likely to cause increased rates of erosion because, in addition to removing ground cover, they can significantly change drainage patterns, especially if an embankment has been made to support the road. A road that has a lot of rock and one that is "hydrologically invisible" (that gets the water off the road as quickly as possible, mimicking natural drainage patterns) has the best chance of not causing increased erosion.
Many human activities remove vegetation from an area, making the soil easily eroded. Logging can cause increased erosion rates due to soil compaction, exposure of mineral soil, for example roads and landings. However it is the removal of or compromise to the forest floor not the removal of the canopy that can lead to erosion. This is because rain drops striking tree leaves coalesce with other rain drops creating larger drops. When these larger drops fall (called throughfall) they again may reach terminal velocity and strike the ground with more energy then had they fallen in the open. Terminal velocity of rain drops is reached in about 8 meters. Because forest canopies are usually higher than this, leaf drop can regain terminal velocity. However, the intact forest floor, with its layers of leaf litter and organic matter, absorbs the impact of the rainfall.[4]
external image 220px-5767-Linxia-Wanshou-Guan-erosion.jpgexternal image magnify-clip.png A Linxia City, China, farmer is gradually losing his land as the edge of the loess plateau is eroded away
Heavy grazing can reduce vegetation enough to increase erosion. Changes in the kind of vegetation in an area can also affect erosion rates. Different kinds of vegetation lead to different infiltration rates of rain into the soil. Forested areas have higher infiltration rates, so precipitation will result in less surface runoff, which erodes. Instead much of the water will go in subsurface flows, which are generally less erosive. Leaf litter and low shrubs are an important part of the high infiltration rates of forested systems, the removal of which can increase erosion rates. Leaf litter also shelters the soil from the impact of falling raindrops, which is a significant agent of erosion. Vegetation can also change the speed of surface runoff flows, so grasses and shrubs can also be instrumental in this aspect.
One of the main causes of erosive soil loss in the year 2006 is the result of slash and burn treatment of tropical forest. When the total ground surface is stripped of vegetation and then seared of all living organisms, the upper soils are vulnerable to both wind and water erosion. In a number of regions of the earth, entire sectors of a country have been rendered unproductive. For example, on the Madagascar high central plateau, comprising approximately ten percent of that country's land area, virtually the entire landscape is sterile of vegetation, with gully erosive furrows typically in excess of 50 meters deep and one kilometer wide. Shifting cultivation is a farming system which sometimes incorporates the slash and burn method in some regions of the world. This degrades the soil and causes the soil to become less and less fertile.


Approximately 40% of the world's agricultural land is seriously degraded.[5] According to the UN, an area of fertile soil the size of Ukraine is lost every year because of drought, deforestation and climate change.[6] In Africa, if current trends of soil degradation continue, the continent might be able to feed just 25% of its population by 2025, according to UNU's Ghana-based Institute for Natural Resources in Africa.[7]
external image 220px-Bank_erosion_5790.JPGexternal image magnify-clip.png Bank erosion started by four wheeler all-terrain vehicles, Yauhanna, South Carolina
When land is overused by animal activities (including humans), there can be mechanical erosion and also removal of vegetation leading to erosion. In the case of the animal kingdom, this effect would become material primarily with very large animal herds stampeding such as the Blue Wildebeest on the Serengeti plain. Even in this case there are broader material benefits to the ecosystem, such as continuing the survival of grasslands, that are indigenous to this region. This effect may be viewed as anomalous or a problem only when there is a significant imbalance or overpopulation of one species.
In the case of human use, the effects are also generally linked to overpopulation. When large number of hikers use trails or extensive off road vehicle use occurs, erosive effects often follow, arising from vegetation removal and furrowing of foot traffic and off road vehicle tires. These effects can also accumulate from a variety of outdoor human activities, again simply arising from too many people using a finite land resource.
One of the most serious and long-running water erosion problems worldwide is in the People's Republic of China, on the middle reaches of the Yellow River and the upper reaches of the Yangtze River. From the Yellow River, over 1.6 billion tons of sediment flows into the ocean each year. The sediment originates primarily from water erosion in the Loess Plateau region of the northwest.



external image 220px-NegevWadi2009.JPGexternal image magnify-clip.png Wadi in Makhtesh Ramon, Israel, showing gravity collapse erosion on its banks.
Mass wasting is the down-slope movement of rock and sediments, mainly due to the force of gravity. Mass movement is an important part of the erosional process, as it moves material from higher elevations to lower elevations where other eroding agents such as streams and glaciers can then pick up the material and move it to even lower elevations. Mass-movement processes are always occurring continuously on all slopes; some mass-movement processes act very slowly; others occur very suddenly, often with disastrous results. Any perceptible down-slope movement of rock or sediment is often referred to in general terms as a landslide. However, landslides can be classified in a much more detailed way that reflects the mechanisms responsible for the movement and the velocity at which the movement occurs. One of the visible topographical manifestations of a very slow form of such activity is a scree slope.
Slumping happens on steep hillsides, occurring along distinct fracture zones, often within materials like clay that, once released, may move quite rapidly downhill. They will often show a spoon-shaped isostatic depression, in which the material has begun to slide downhill. In some cases, the slump is caused by water beneath the slope weakening it. In many cases it is simply the result of poor engineering along highways where it is a regular occurrence.
Surface creep is the slow movement of soil and rock debris by gravity which is usually not perceptible except through extended observation. However, the term can also describe the rolling of dislodged soil particles 0.5 to 1.0 mm in diameter by wind along the soil surface.


external image 220px-Tregastel_Brittany_France_Curious_Stone.jpgexternal image magnify-clip.png Nearly perfect sphere in granite, Trégastel, Brittany.
Splash erosion is the detachment and airborne movement of small soil particles caused by the impact of raindrops on soil.
Sheet erosion is the detachment of soil particles by raindrop impact and their removal downslope by water flowing overland as a sheet instead of in definite channels or rills. The impact of the raindrop breaks apart the soil aggregate. Particles of clay, silt and sand fill the soil pores and reduce infiltration. After the surface pores are filled with sand, silt or clay, overland surface flow of water begins due to the lowering of infiltration rates. Once the rate of falling rain is faster than infiltration, runoff takes place. There are two stages of sheet erosion. The first is rain splash, in which soil particles are knocked into the air by raindrop impact. In the second stage, the loose particles are moved downslope by broad sheets of rapidly flowing water filled with sediment known as sheetfloods. This stage of sheet erosion is generally produced by cloudbursts, sheetfloods commonly travel short distances and last only for a short time.
Rill erosion refers to the development of small, ephemeral concentrated flow paths, which function as both sediment source and sediment delivery systems for erosion on hillslopes. Generally, where water erosion rates on disturbed upland areas are greatest, rills are active. Flow depths in rills are typically on the order of a few centimeters or less and slopes may be quite steep. These conditions constitute a very different hydraulic environment than typically found in channels of streams and rivers. Eroding rills evolve morphologically in time and space. The rill bed surface changes as soil erodes, which in turn alters the hydraulics of the flow. The hydraulics is the driving mechanism for the erosion process, and therefore dynamically changing hydraulic patterns cause continually changing erosional patterns in the rill. Thus, the process of rill evolution involves a feedback loop between flow detachment, hydraulics, and bed form. Flow velocity, depth, width, hydraulic roughness, local bed slope, friction slope, and detachment rate are time and space variable functions of the rill evolutionary process. Superimposed on these interactive processes, the sediment load, or amount of sediment in the flow, has a large influence on soil detachment rates in rills. As sediment load increases, the ability of the flowing water to detach more sediment decreases.
Where precipitation rates exceed soil infiltration rates, runoff occurs. Surface runoff turbulence can often cause more erosion than the initial raindrop impact.
Gully erosion, also called ephemeral gully erosion, occurs when water flows in narrow channels during or immediately after heavy rains or melting snow. This is particularly noticeable in the formation of hollow ways, where, prior to being tarmacked, an old rural road has over many years become significantly lower than the surrounding fields.
A gully is sufficiently deep that it would not be routinely destroyed by tillage operations, whereas rill erosion is smoothed by ordinary farm tillage. The narrow channels, or gullies, may be of considerable depth, ranging from 1 to 2 feet to as much as 75 to 100 feet. Gully erosion is not accounted for in the revised universal soil loss equation.
Valley or stream erosion occurs with continued water flow along a linear feature. The erosion is both downward, deepening the valley, and headward, extending the valley into the hillside. In the earliest stage of stream erosion, the erosive activity is dominantly vertical, the valleys have a typical V cross-section and the stream gradient is relatively steep. When some base level is reached, the erosive activity switches to lateral erosion, which widens the valley floor and creates a narrow floodplain. The stream gradient becomes nearly flat, and lateral deposition of sediments becomes important as the stream meanders across the valley floor. In all stages of stream erosion, by far the most erosion occurs during times of flood, when more and faster-moving water is available to carry a larger sediment load. In such processes, it is not the water alone that erodes: suspended abrasive particles, pebbles and boulders can also act erosively as they traverse a surface.
At extremely high flows, kolks, or vortices are formed by large volumes of rapidly rushing water. Kolks cause extreme local erosion, plucking bedrock and creating pothole-type geographical features called Rock-cut basins. Examples can be seen in the flood regions result from glacial Lake Missoula, which created the channeled scablands in the Columbia Basin region of eastern Washington.[8]
Bank erosion is the wearing away of the banks of a stream or river. This is distinguished from changes on the bed of the watercourse, which is referred to as scour. Erosion and changes in the form of river banks may be measured by inserting metal rods into the bank and marking the position of the bank surface along the rods at different times.[9]


Main article: Coastal erosionSee also: Beach evolutionexternal image 220px-12_Venus_Bay_32.JPGexternal image magnify-clip.png Erosion due to wave pounding at Venus Bay, South Australia.external image 220px-Wavecut_platform_southerndown_pano.jpgexternal image magnify-clip.pngWave cut platform caused by erosion of cliffs by the sea, at Southerndown in South Wales
Shoreline erosion, which occurs on both exposed and sheltered coasts, primarily occurs through the action of currents and waves but sea level (tidal) change can also play a role.
Hydraulic action takes place when air in a joint is suddenly compressed by a wave closing the entrance of the joint. This then cracks it. Wave pounding is when the sheer energy of the wave hitting the cliff or rock breaks pieces off. Abrasion or corrasion is caused by waves launching seaload at the cliff. It is the most effective and rapid form of shoreline erosion (not to be confused with corrosion). Corrosion is the dissolving of rock by carbonic acid in sea water. Limestone cliffs are particularly vulnerable to this kind of erosion. Attrition is where particles/seaload carried by the waves are worn down as they hit each other and the cliffs. This then makes the material easier to wash away. The material ends up as shingle and sand. Another significant source of erosion, particularly on carbonate coastlines, is the boring, scraping and grinding of organisms, a process termed bioerosion.
Sediment is transported along the coast in the direction of the prevailing current (longshore drift). When the upcurrent amount of sediment is less than the amount being carried away, erosion occurs. When the upcurrent amount of sediment is greater, sand or gravel banks will tend to form. These banks may slowly migrate along the coast in the direction of the longshore drift, alternately protecting and exposing parts of the coastline. Where there is a bend in the coastline, quite often a build up of eroded material occurs forming a long narrow bank (a spit). Armoured beaches and submerged offshore sandbanks may also protect parts of a coastline from erosion. Over the years, as the shoals gradually shift, the erosion may be redirected to attack different parts of the shore.


Ice erosion can take one of two forms. It can be caused by the movement of ice, typically as glaciers, in a process called glacial erosion. It can also be due to freeze-thaw processes in which water inside pores and fractures in rock may expand cause further cracking.
Glaciers erode predominantly by three different processes: abrasion/scouring, plucking, and ice thrusting. In an abrasion process, debris in the basal ice scrapes along the bed, polishing and gouging the underlying rocks, similar to sandpaper on wood. Glaciers can also cause pieces of bedrock to crack off in the process of plucking. In ice thrusting, the glacier freezes to its bed, then as it surges forward, it moves large sheets of frozen sediment at the base along with the glacier. This method produced some of the many thousands of lake basins that dot the edge of the Canadian Shield. These processes, combined with erosion and transport by the water network beneath the glacier, leave moraines, drumlins, ground moraine (till), kames, kame deltas, moulins, and glacial erratics in their wake, typically at the terminus or during glacier retreat.
Cold weather causes water trapped in tiny rock cracks to freeze and expand, breaking the rock into several pieces. This can lead to gravity erosion on steep slopes. The scree which forms at the bottom of a steep mountainside is mostly formed from pieces of rock (soil) broken away by this means. It is a common engineering problem wherever rock cliffs are alongside roads, because morning thaws can drop hazardous rock pieces onto the road.
In some places, water seeps into rocks during the daytime, then freezes at night. Ice expands, thus, creating a wedge in the rock. Over time, the repetition in the forming and melting of the ice causes fissures, which eventually breaks the rock down.


external image 220px-Im_Salar_de_Uyuni.jpgexternal image magnify-clip.png A rock formation in the Altiplano, Bolivia sculpted by wind erosion.external image 220px-MoabAlcove.JPGexternal image magnify-clip.png Wind-eroded alcove near Moab, Utah.Main article: Aeolian processes
In arid climates, the main source of erosion is wind.[10] The general wind circulation moves small particulates such as dust across wide oceans thousands of kilometers downwind of their point of origin,[11] which is known as deflation. Erosion can be the result of material movement by the wind. There are two main effects. First, wind causes small particles to be lifted and therefore moved to another region. This is called deflation. Second, these suspended particles may impact on solid objects causing erosion by abrasion (ecological succession). Wind erosion generally occurs in areas with little or no vegetation, often in areas where there is insufficient rainfall to support vegetation. An example is the formation of sand dunes, on a beach or in a desert.[12] Loess is a homogeneous, typically nonstratified, porous, friable, slightly coherent, often calcareous, fine-grained, silty, pale yellow or buff, windblown (aeolian) sediment.[13] It generally occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess often stands in either steep or vertical faces.[14] Loess tends to develop into highly rich soils. Under appropriate climatic conditions, areas with loess are among the most agriculturally productive in the world.[15] Loess deposits are geologically unstable by nature, and will erode very readily. Therefore, windbreaks (such as big trees and bushes) are often planted by farmers to reduce the wind erosion of loess.[10]


Thermal erosion is the result of melting and weakening permafrost due to moving water.[16] It can occur both along rivers and at the coast. Rapid river channel migration observed in the Lena River of Siberia is due to thermal erosion, as these portions of the banks are composed of permafrost-cemented non-cohesive materials.[17] Much of this erosion occurs as the weakened banks fail in large slumps. Thermal erosion also affects the Arctic coast, where wave action and near-shore temperatures combine to undercut permafrost bluffs along the shoreline and cause them to fail. Annual erosion rates along a 100-kilometer segment of the Beaufort Sea shoreline averaged 5.6 meters per year from 1955 to 2002.[18]

Soil erosion and climate change

The warmer atmospheric temperatures observed over the past decades are expected to lead to a more vigorous hydrological cycle, including more extreme rainfall events.[19] In 1998 Karl and Knight reported that from 1910 to 1996 total precipitation over the contiguous U.S. increased, and that 53% of the increase came from the upper 10% of precipitation events (the most intense precipitation).[20] The percent of precipitation coming from days of precipitation in excess of 50 mm has also increased significantly.
Studies on soil erosion suggest that increased rainfall amounts and intensities will lead to greater rates of erosion. Thus, if rainfall amounts and intensities increase in many parts of the world as expected, erosion will also increase, unless amelioration measures are taken. Soil erosion rates are expected to change in response to changes in climate for a variety of reasons. The most direct is the change in the erosive power of rainfall. Other reasons include: a) changes in plant canopy caused by shifts in plant biomass production associated with moisture regime; b) changes in litter cover on the ground caused by changes in both plant residue decomposition rates driven by temperature and moisture dependent soil microbial activity as well as plant biomass production rates; c) changes in soil moisture due to shifting precipitation regimes and evapo-transpiration rates, which changes infiltration and runoff ratios; d) soil erodibility changes due to decrease in soil organic matter concentrations in soils that lead to a soil structure that is more susceptible to erosion and increased runoff due to increased soil surface sealing and crusting; e) a shift of winter precipitation from non-erosive snow to erosive rainfall due to increasing winter temperatures; f) melting of permafrost, which induces an erodible soil state from a previously non-erodible one; and g) shifts in land use made necessary to accommodate new climatic regimes.
Studies by Pruski and Nearing indicated that, other factors such as land use not considered, we can expect approximately a 1.7% change in soil erosion for each 1% change in total precipitation under climate change.[21]

Tectonic effects

external image 220px-River_eroding_volcanic_ash_flow_Alaska_Southwest%2C_Valley_of_Ten_Thousand_Smokes.jpgexternal image magnify-clip.png River eroding volcanic ash flow Alaska Southwest, Valley of Ten Thousand Smokes
The removal by erosion of large amounts of rock from a particular region, and its deposition elsewhere, can result in a lightening of the load on the lower crust and mantle. This can cause tectonic or isostatic uplift in the region. Research undertaken since the early 1990s suggests that the spatial distribution of erosion at the surface of an orogen can exert a key influence on its growth and its final internal structure (see erosion and tectonics).[22]

Materials science

In materials science, erosion is the recession of surfaces by repeated localized mechanical trauma as, for example, by suspended abrasive particles within a moving fluid. Erosion can also occur from non-abrasive fluid mixtures. Cavitation is one example.
In hard particle erosion, the hardness of the impacted material is a large factor in the mechanics of the erosion. A soft material will typically erode fastest from glancing impacts.[23] Harder material will typically erode fastest from perpendicular impacts. Hardness is a correlative factor for erosion resistance, but a higher hardness does not guarantee better resistance. Factors that affect the erosion rate also include impacting particle speed, size, density, hardness, and rotation. Coatings can be applied to retard erosion, but normally can only slow the removal of material. Erosion rate for solid particle impact is typically measured as mass of material removed divided by the mass of impacting material.[24]

Officials fear the death toll may rise to over 2,000 from the recent earthquake in Colombia. The massive destruction left the country looking like a bombed-out relic of a war zone, with an estimated 200,000 left homeless, and many without clean water, sewage disposal, electricity or adequate food. Hurricane Mitch left 23,500 dead or missing in Central America.

Are upset weather conditions, earthquakes and natural disasters on the increase worldwide? Are there spiritual causes behind them or are they just the result of random, environmental happenings? Do disasters have any meaning or message for humankind today?