Earth’s atmosphere

Breathe in deeply... Breathe out slowly, and let the air leave your body… And go where?! Good question! Well, the air you breathe stays right here … … in the layer of gas that surrounds the Earth - the atmosphere. Earth’s atmosphere is made up of a mix of different gases, mostly nitrogen and oxygen, as well as small amounts of argon, carbon dioxide, water vapour, and other gases.

The gas particles are pulled towards the Earth by gravitational force. Gravitational force is strongest close to the surface of the planet, so the atmosphere is thickest there, and it thins out as the altitude increases. Temperature also changes with altitude! Based on these changing characteristics, Earth’s atmosphere can be divided into five distinct layers. The first layer, which is closest to the Earth’s surface, is around 7 to 20 kilometers thick.

It’s highest at the equator, and lowest at the North and South Poles. This layer contains about half of the mass of gases that surround our planet. It also contains most of the water vapour in the atmosphere. This is the troposphere. The air in the troposphere heats up close to the Earth’s surface, and gets colder higher up.

This causes the air to circulate and move around, as wind. The troposphere also contains small particles, such as dust, around which water vapour can condense, forming clouds. So, the troposphere is where most weather occurs. The second layer of the atmosphere stretches from the end of the troposphere to about 50 kilometers above the ground. The air here is about a thousand times thinner than at sea level.

This is the stratosphere. The temperature in the stratosphere increases with altitude. This is because of a layer of gas called ozone. The ozone layer absorbs some of the radiation from the sun. This traps in heat and protects the Earth from harmful radiation.

The third layer of the atmosphere starts above the stratosphere and extends up to 85 kilometers. The air here is thinner than in the stratosphere, yet still thick enough to cause meteors to burn up as they pass through. This layer is the mesosphere. Mesosphere is the coldest layer of the atmosphere, and temperature here decreases with altitude. At the top of the mesosphere, the temperature is about minus 90 degrees Celsius!

It’s so cold that water vapour freezes into ice, and can form “shining” ice-crystal clouds. The fourth layer of the atmosphere extends from the end of the mesosphere to between 500 and 1000 kilometers high. The air here is so thin that upper parts of this layer are sometimes considered to be outer space. This is the thermosphere. Solar radiation makes the thermosphere very hot.

The temperatures can reach 2000 degrees Celsius! The thermosphere is where satellites, including the International Space Station orbit the earth. The thermosphere contains a layer of ionised gas known as the ionosphere, where spectacular bright lights - auroras - occur. The fifth, outermost layer has no upper boundary. It is made up of widely dispersed particles of helium and hydrogen.

This is the exosphere. Gravitational pull acting on the particles in the exosphere is so low that the particles can escape. Here, the earth’s atmosphere transitions into space. Earth's atmosphere is extremely important. It stabilises the Earth’s temperature and pressure, allowing for liquid water to exist, protects Earth from harmful solar radiation, and provides air for organisms to breathe... ...in...

and out... Breathe in… and out…