What is the earth’s atmosphere made of?

The atmosphere is everything above the Earth’s surface, reaching straight upwards roughly 10,000 km (6,214 miles) into space. Everything beyond this distance is considered to be outer space. While the Earth’s atmosphere does reach very far out, the denser portion is located much closer to the surface, at a distance of 8 to 15 km away. About 75% of the atmosphere’s mass is found in this dense portion. This is why higher elevations can be described as having “thinner” atmospheres, and why climbing large mountains or increasing elevation at speed can often cause altitude sickness. This “sickness” is the human body’s reaction to being in a less hospitable environment, an area with thinner air that does not have as strong a concentration of the gases we are accustomed to.

The drop in air pressure is why we can feel popping in our ears when we increase altitude. This low pressure happens because there is less gravitational force in the top portions of the atmosphere than there is closer to the surface, where all of the atmosphere’s weight can be felt.

The troposphere is not the same thickness all over the Earth. It is actually known to be at its thinnest at the South and North Poles and thicker around the equator. As you rise within the troposphere, temperatures begin to decrease. On top of this layer is what is referred to as the tropopause.

The stratosphere is the second layer of the atmosphere just above the troposphere. It ranges from approximately 15 km above the earth’s surface to 50 km (30 miles) above the Earth. The stratosphere is most well known for having a large amount of ozone gas, an oxygen compound. Because of this, this region is often referred to as the “ozone layer.”

The ozone layer is often referenced in relation to climate change, or referred to as having a “hole” in it. This is important because the ozone forms a protective barrier between the sun’s harsh rays and life on earth. Without this barrier, temperatures would rise, and sun exposure would increase, making the earth uninhabitable.

The next layer in the Earth’s atmosphere is known as the mesosphere. The mesosphere reaches 85 km (53 miles) out from the surface of the earth. It is very cold, with the coldest temperatures found at the top of this layer where it can reach -90 °C (-130 °F). The atmosphere is much thinner here than it is closer to the Earth, but there is still enough density to cause space debris to burn when it enters this layer. This is why we see shooting stars, which are space rocks burning through the mesosphere. In the same way, spacecraft need special heat-resistant shells to ensure the structures do not burn when passing through or re-entering the mesosphere. Like the previous layers, the mesosphere is topped by a pause, this one called the mesopause.

Above the mesopause, ending some 600 km (372 miles) from the surface of the Earth is the thermosphere.

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