What is the Earth's structure primarily composed of?

The Earth's structure is primarily composed of a crust and a hot mantle, which is the most accurate representation of its layered composition. The crust is the outermost layer where we live, consisting of solid rock, while beneath it lies the mantle, which extends deep into the Earth and is primarily solid but behaves like a viscous fluid over long periods of time due to the extreme heat and pressure. This heat causes convection currents within the mantle, driving plate tectonics and geological activity.

The other options misrepresent significant aspects of Earth's composition. There is no core made entirely of gas; the core is known to be primarily composed of iron and nickel and exists in a liquid state in the outer core and a solid state in the inner core. A description of Earth composed solely of solid rock overlooks the crucial layers, particularly the mantle, which has different states of matter and behaviors. Additionally, a gaseous outer layer is incorrect because while the atmosphere is indeed a layer surrounding the Earth, it is not part of the Earth's internal structure. Therefore, the characterization of Earth's structure as having a crust and a hot mantle correctly illustrates the layers that make up the planet.