What does the atmosphere consist of?

The atmosphere is composed of a mixture of gases that surround a planet. In the case of Earth, this includes gases such as nitrogen (about 78%), oxygen (about 21%), argon, carbon dioxide, and trace amounts of other gases. These gases are essential for life, as they provide the air we breathe and play crucial roles in weather, climate, and various biological processes.

The other choices describe different components related to Earth but do not pertain to the atmosphere. The solid crust refers to the outermost layer of the Earth, while the water covering the Earth pertains to the hydrosphere. The internal liquid layers relate to Earth's mantle and core, which are involved in geological processes but are not part of the atmospheric composition. Thus, the correct answer highlights the crucial aspect of the atmosphere as a layer of gases surrounding the planet.