The four agents of erosion, or the transport and removal the products of weathering, are water, wind, gravity, and glaciers. *Note: water and ice are sometimes thought as one agent, making three agents of erosion total (water, wind, and gravity).

Water, whether in the form of a stream, an ocean, or even heavy precipitation, transports sediments. In the image below, the water has worn away the rock and these rock sediments have been transported elsewhere.

During wind erosion, moving sediments are picked up by the wind and are transported depending on the strength of the wind and the mass of the sediment.

Gravity also causes erosion. This process can happen gradually over time or more quickly, such as during a landslide or avalanche.

Finally, glaciers transport sediment when they move. This process occurs very slowly, but as a glacier moves across land, it picks up and distributes sediments. In the image below, you can see how the contact between the ice and the earth disrupts sediments. These sediments become trapped in the ice and moved.

As you can see in the image below, glaciers aren't just ice.

The main parts of the Compressor Stations include the following-

Compressor Unit – The compressor unit is the piece of equipment which actually compresses the gas. It can work in any of the following ways-

• Turbines with Centrifugal Compressors –
  This type of compressor is mainly powered by a turbine to turn a centrifugal compressor and that centrifugal compressor is powered by natural gas.

• Electric Motors with Centrifugal Compressors –
  This type of compressor also takes help of the centrifugal compressors to compress the gas.
  The difference is just that they rely on high voltage electric motors.

• Reciprocating Compressor–
  This type of compressor uses a large piston engines to crank reciprocating pistons located within cylindrical cases on the side of the unit. These pistons compress the gas.
  These engines are also fueled by natural gas.

Filters and Scrubbers– These just remove water, and other impurities from the natural gas.

Gas Cooling Systems –
When the natural gas is compressed its temperature rises.
So for this the gas is made to travel through a cooling sector. Which cools down the temperature of the gas so the pipeline is not damaged through which the gas is travelling.

Mufflers –
These are basically the Noise controllers of the Compressor Stations.

A carbon sink is growing in size and storing more carbon compared to a carbon source which is shrinking in size and releasing more carbon.

Carbon sources include emissions from burning fossil fuels, forest fires, and respiration. Carbon sinks include the oceans, plants, and soil.

This image shows sinks in blue and fluxes or changes in carbon in red:

Typically, sources and sinks balance one another. For example, the carbon emitted during respiration is offset by photosynthesis (see the image above). However, the burning of fossil fuels is an important carbon source.

The image below shows natural processes in black and anthropogenic or human-influenced processes in red:

To learn more about carbon sources and sinks, see this page.

Check out this interactive carbon map by the GLOBE Carbon Cycle Project.

Ancient people of China, Peru, Mesopotamia, Indus valley and Nile valley became engaged in farming at least 10,000 years ago. Pigs were domesticated in Mesopotamia 13,000 years ago followed by domestication of sheep and cattle in nearby areas. This is why, fertile crescent of near east is regarded as the birthplace of agriculture, and it is here, man first cultivated wheat.

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That does not mean that contributions from other centres are of less importance. Maize, papaya and potato were domesticated in the New World; edible mango, orange, tamarind and spices originated in south east Asia; while litchi and onions were first cultivated in China.

The layers of the atmosphere from bottom to top are the troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere.

We live in the troposphere and most of our weather comes from this layer of the atmosphere.

The next layer up is the stratosphere , which is where the ozone layer is found and where planes flying long distances tend to fly.

If you're ever watching a meteor shower, you're looking at meteors in the mesosphere, the third layer of the atmosphere.

The next layer is the thermosphere, which is where the International Space Shuttle can be found. This layer spans from around 80km to 550km above the Earth's surface and this is the largest layer of the atmosphere (see image below). There are no clouds in the thermosphere. This is where the aurora borealis is.

The final layer is the exosphere. Most satellites are in the exosphere and the aurora borealis occasionally occurs in the very lowest portion of the exosphere.

Generally evolution is divergent: I say so because that is how this earth has today become home to immensely diverse kinds of life.

• Divergent evolution simply means appearance of more than one descendant species from an ancestral species population. Mammalian forelimbs, for example, follow an ancestral pentadactyl limb plan but work very differently in different orders.
• Divergent evolution may lead to appearance of homologous organs. Divergence appears due to adaptation of related organisms in different environmental conditions and habit.

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• We also find organisms which evolved superficial/plastic similarity in appearance or similar adaptations in habit to other organisms, with which they are not closely related. This is convergent evolution as exhibited by shark and dolphin: they belong to different vertebrate class but both are adapted to aquatic life.
• Convergent evolution leads to appearance of analogous organs where infrastructure of such organs may differ but the functional achievement remains same. This is because of the fact that similarity in appearance and behaviour evolves due to similar environmental pressure.

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