Earth’s Atmosphere

Earth’s atmosphere consists of mostly nitrogen and oxygen. The atmosphere also blocks out some of the sun’s rays, ensuring that it is not too hot or bright. The atmosphere is divided into 5 layers. The lowest of the layers is the densest, and the layer farthest away is the lightest.

Troposphere

The troposphere is the layer closest to the Earth. It starts at the Earth’s surface and reaches about 6 miles(about 10 kilometers) high. The troposphere consists of most of the atmosphere, about 75 percent of it. Most clouds and almost all weather occurs in this layer. Clouds rarely form in the above layer because not much water vapor reaches it. The water vapor forms into clouds in the troposphere. As you get higher up in the troposphere, the air around you gets cooler.

Stratosphere

The stratosphere is the layer right above the troposphere. It covers a range of about 6 miles(10 km) to 31 miles(50 km) high. The usual height of a flying plane would be in the lower stratosphere to reduce weather conditions and turbulence. The stratosphere is much dryer than the troposphere because of the rarity of water droplets. Strangely enough, the stratosphere is also hotter! This is because of a gas called Ozone, which is common in the stratosphere. Ozone absorbs a lot of the sun’s ultraviolet radiation, heating the stratosphere up. Unlike the troposphere, the air gets warmer as you reach a higher altitude.

Mesosphere

The mesosphere, right above the stratosphere, covers a range of about 31 miles(50 km) to 53 miles(85 km). The mesosphere is difficult to study, because weather balloons or aircrafts cannot reach its height. We do know that most meteors that enter the Earth’s atmosphere vaporize in the mesosphere, causing bits of iron and other metal to linger in this layer. As you get higher up, the temperature decreases.

Thermosphere

We know more about the thermosphere because of satellites orbiting in the layer above. These satellites can give information about the thermosphere. The thermosphere starts at 53 miles(85 km) to between 300 miles(500 km) and 621 miles(1000 km). The air in it is mostly nitrogen, but there is also oxygen. In the upper thermosphere there are even a few molecules of helium. The temperatures here are extremely high because of the direct contact of the sun’s rays. The air in the thermosphere is very low in density. Some aircrafts orbit the Earth in the thermosphere, like the International Space Station.

Exosphere

The exosphere is the last part of our atmosphere. It is extremely thin and very similar to the airless space above it. In fact, some scientists even consider it part of space instead of our atmosphere. There is no clear upper boundary of the exosphere, because it just melts into space. The exosphere begins where the thermosphere ends. Most molecules of gas located in the exosphere stay there or gradually descend deeper into the Earth’s atmosphere, but some fast moving molecules actually float away into space! Because of this, the exosphere grows smaller every year.