Which layer of the Earth is NOT part of the geosphere?

The atmosphere is the correct choice as it is not part of the geosphere. The geosphere refers specifically to the solid parts of Earth, which include the crust, mantle, and core. These components are composed of rocks and minerals that make up the Earth's structure.

The atmosphere, on the other hand, is a layer of gases surrounding the planet and is crucial for supporting life by providing oxygen and protecting the Earth from harmful solar radiation. This gaseous layer forms a significant part of Earth's system but does not involve solid materials, which is why it is not included in the definition of the geosphere. Understanding these distinctions helps clarify the different components of Earth's system and their roles in the environment.