Thursday, February 28, 2013

Earth’s atmosphere

Earth’s atmosphere is an amazing thing, when you think about it. Without our atmosphere life would be unsustainable here on Earth; but what exactly is it? 

The atmosphere is simply a layered mixture of gases, mainly nitrogen (78%), Oxygen (21%) and a mixture of argon, water vapour, carbon dioxide, methane and trace gases. These combined create not only the air we breathe, but also help serve as a sun screen, a temperature regulator and of course protect us from asteroid impacts (most of the time!).

The innermost layer of our atmosphere, and probably the most familiar to us, is the troposphere. Here and up until around 15km from the surface is where the majority of our planets weather systems reside and is where nearly 80% of the Earth’s air is located. The name “troposphere” comes from a Greek word that refers to mixing and this is exactly what happens within the troposphere, as warm air rises to form clouds, rain falls, and winds stir the lands below.

Past the troposphere we discover the stratosphere; a less dense region of the atmosphere which extends out to around 50km. Here, the oxygen molecules are transformed into ozone which forms a protective layer against harmful ultraviolet light from the sun- the importance of this layer has been made evident in our lifetimes; without which, skin cancer rates would be undoubtedly higher. Seeing as ultraviolet energy is being absorbed in this region, the stratosphere has quite extravagant differentials in temperature. At the base of the stratosphere it is extremely cold, around -80 degrees Celsius, at its top, the temperature rises to nearly 0 degrees Celsius.

After the stratosphere comes the mesosphere and here is where a lot of action happens. Any meteors which enter our atmosphere tend to be destroyed in the mesosphere; they “burn up” and never reach the Earth’s surface. This layer, which extends to 85 kilometres from the surface, is one of the fundamental reasons why Earth isn’t covered in meteor craters- if the moon had a mesosphere it would be a much smoother surface.

Next comes the ionosphere- named for the ions created within this layer from energetic particles of sunlight and space. The ionosphere allows for the transmission of radio signals which are invaluable, particularly before the days of satellite communication. Here is also were the auroras are created and who doesn’t love them, eh? The International Space Station has also made its home in the ionosphere.

Lastly, we have the exosphere. This tenuous portion of the Earth's atmosphere extends outward until it interacts with the solar wind. Solar storms compress the exosphere. When the Sun is tranquil, the layer can extend further outward. The reach of this layer varies between 1,000 and 10,000 kilometres, where it merges with interplanetary space.

Together, all these layers make our atmosphere which, sadly, is continually menaced by human activity. Between rising carbon dioxide levels and air pollution, ozone destruction and acid rain, we have divorced our relationship with our environment. It is important not to forget the delicacy which is life here on Earth, we should aim to maintain a mutually beneficial relationship with what has supported our time here on this lovely blue planet. After all, if the relationship is irreconcilable, the environment will get the house... !

Some further information and reading for you:

Photo was taken from the ISS (credit: NASA/SPL)

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