Concept:The earth's solid body is layered internally, with the outermost layer called the crust.
Explanation:The solid earth consists of three main layers: the crust, the mantle, and the core.
The crust is the thin, outermost solid layer of the earth.
The mantle is located below the crust and extends towards the interior.
The core is the innermost layer of the earth, making option A incorrect.
The atmosphere is the gaseous layer surrounding the earth, not part of the solid earth's outer layer, so option B is incorrect.
The hydrosphere includes all water bodies, which are not part of the solid outer layer, so option D is incorrect.
Hence, the outer layer of the solid earth is correctly identified as the crust.
Answer:C. crust