Earth's Water and Interior Structure
The hydrosphere includes all of Earth's water—oceans, lakes, rivers, groundwater, and even water vapor. About 75% of Earth's surface is covered with liquid water, constantly cycling through the hydrologic cycle: evaporation, condensation, precipitation, and accumulation.
Below the water and land surface lies the lithosphere—Earth's outer shell consisting of the crust and uppermost portion of the mantle. Think of Earth's structure like a peach: the skin is the crust, the flesh is the mantle, and the pit is the core.
The crust is Earth's outermost layer, divided into continental crust (sial) and oceanic crust (sima). Below this lies the mantle, a semi-molten layer making up about 80% of Earth's volume. The mantle includes the asthenosphere, a relatively soft layer that allows the plates above to move.
Mind-blowing fact: Earth's inner core is actually solid despite being hotter than the outer core! The immense pressure at Earth's center prevents the metal from melting.
At Earth's center is the core, consisting of an outer liquid layer and a solid inner core made primarily of iron. The boundaries between these layers have special names: the Mohorovicic Discontinuity between crust and mantle, the Gutenberg Discontinuity between mantle and core, and the Lehmann Discontinuity between outer and inner core.