What is the outermost layer of the Earth known as?

The outermost layer of the Earth, when considering the structure of the atmosphere, is referred to as the thermosphere. This layer is situated above the mesosphere and below the exosphere, extending from about 80 kilometers (50 miles) above the Earth's surface to the edge of space, at around 600 kilometers (370 miles).

The thermosphere is characterized by a dramatic increase in temperature with altitude, primarily due to the absorption of solar radiation. This layer is also where the auroras occur, as it contains a small number of particles that can become ionized by solar activity. The thinning atmosphere in the thermosphere means that even though temperatures are extremely high, there are very few air molecules present, making it feel quite cold to a spacecraft or satellite passing through it.

Understanding the structure of the Earth's layers is crucial, as it helps distinguish between atmospheric layers and geological layers, such as the Earth's crust, mantle, and core. The other terms mentioned—troposphere, mesosphere, and stratosphere—represent different layers of the atmosphere beneath the thermosphere, with each having distinct characteristics and roles in Earth's climatic and weather systems.