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Secondary I • 11mo.

What is the atmosphere composed of and how do humans affect its composition? Thanks a lot!

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  • Explanation from Alloprof

    Explanation from Alloprof

    This Explanation was submitted by a member of the Alloprof team.

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    Team Alloprof • 11mo.

    Thank you for your question!

    Earth's atmosphere is the gaseous layer that envelops the Earth.

    Many gases constitute this layer:

    The main constituent of the atmosphere is dinitrogen (at 78.1% of the atmosphere). This gas cannot be used by most living organisms for any metabolic process. In decreasing order of importance, the next most common gas is oxygen (at 20.9% of the atmosphere).

    Dioxygen is necessary for most life forms on Earth (including humans), since it is used for cellular respiration.

    Another important atmospheric gas is carbon dioxide. Though it only accounts for 0.035% of the atmosphere, it is a major greenhouse gas, meaning that it captures heat from the sun's rays, thus warming the Earth.

    The atmosphere is often divided into five layers:

    • The troposphere (from sea level (0 km) to 12 km above sea level): the layer in which we live, where 90% of the air in the atmosphere is found, and where meteorological phenomena occur. Planes fly through this layer. For every extra kilometre of altitude, the temperature drops by 10 °C.

    • The stratosphere (12 km to 50 km altitude): the layer that contains the ozone layer and where only 9% of the atmosphere’s air can be found. Jets fly through this layer. The trend of decreasing temperatures reverses, making way for warmer temperatures than in the troposphere.

    • The mesosphere (50 to 85 km altitude): the layer where meteors disintegrate, giving rise to shooting stars. The temperature decreases the higher one goes, with temperatures getting as low as -85 ° C.

    • The thermosphere (85 to 500 km altitude): the layer where air is scarce, northern lights (aurora borealis) occur, and the temperature is very high. Interesting fact: it is from 100 km that we consider that outer space begins. 

    • The exosphere (over 500 km altitude): the layer where space shuttles travel.

    To answer the second part of your question: humans have an impact on several characteristics of the atmosphere. The best known is undoubtedly air pollution. For example, some chemicals such as chlorofluorocarbons (CFCs) have greatly diminished the ozone layer. The prolonged emission of greenhouse gases (GHG) by human activities has modified the composition of the atmosphere by increasing the abundance of carbon dioxide in the atmosphere, making the atmosphere warmer, on average.

    Feel free to ask more questions if you have any!