What is the composition of the Earth's crust?

The composition of the Earth's crust is primarily made up of solid rock. The crust is the outermost layer of the Earth and varies in thickness, being thicker under continents and thinner under oceans. This solid rock is composed of various minerals and elements, providing the physical structure that supports ecosystems and human activities on the surface. Granite and basalt are two common types of rock found in the Earth's crust.

In contrast, the other options describe states of matter or materials that do not accurately represent the crust. Liquid rock refers to magma, which is found deeper in the Earth, while solid metal is more characteristic of the Earth's core. Gaseous materials pertain to the atmosphere and do not comprise the solid foundation of the Earth's surface. Thus, understanding that the Earth's crust is primarily solid rock is fundamental in the study of geology and Earth sciences.