UPCAT Earth Science Practice Test

The outer solid layer of the Earth is referred to as the lithosphere. This term encompasses both the Earth's crust and the uppermost part of the mantle. The lithosphere is characterized by its rigid and brittle nature, which allows it to float on the semi-fluid asthenosphere beneath it.

The crust, while often thought of as the outermost layer, is technically a component of the lithosphere. The distinction is that the lithosphere includes not just the crust, but also the underlying solid upper mantle, making it the correct term when referring to the entire outer solid layer.

The asthenosphere lies directly beneath the lithosphere and is composed of partially molten rock, which allows for some movement; this is why the lithosphere can be considered rigid in comparison. The core is the innermost layer of the Earth, consisting of a solid inner core and a liquid outer core, and is not part of the outer solid layer.