Which sphere is the solid Earth and the largest among the four?

• A. Atmosphere
• B. Biosphere
• C. Geosphere
• D. Hydrosphere

Answer: (C)

The solid Earth is called the geosphere, which includes the rocks, minerals, soil, and the planet’s interior from crust down through the mantle and core. It is the largest of the four spheres because it contains most of Earth's volume and mass. The hydrosphere covers all water—oceans, lakes, rivers, groundwater, and ice—but its total volume is tiny in comparison to the geosphere. The atmosphere is just a thin gaseous layer wrapping around the planet, and the biosphere exists where life interacts with the other spheres but occupies far less volume. So, the geosphere—the solid Earth—is the biggest sphere.