Which term describes the outermost layer of the Earth’s atmosphere?

The outermost layer of the Earth’s atmosphere is known as the thermosphere. This layer extends from approximately 85 km (53 miles) above the Earth’s surface to the edge of space, around 600 km (373 miles) or more. The thermosphere is characterized by a significant increase in temperature with altitude due to the absorption of high-energy solar radiation by sparse air molecules. This layer is also where the auroras occur and where the International Space Station orbits, illustrating its importance in both atmospheric science and human activities in space.

In contrast, the other layers of the atmosphere serve different roles. The troposphere is the lowest layer, where weather occurs and the majority of atmospheric mass is found. The stratosphere lies above the troposphere and contains the ozone layer, which absorbs and scatters ultraviolet solar radiation. The mesosphere is situated above the stratosphere and is known for its decreasing temperatures with height, as well as being where most meteors burn up upon entering the Earth's atmosphere. Each layer has distinct characteristics and functions, making the thermosphere the correct answer for describing the outermost layer.