why Earth’s internal structure varies between viscous (mantle), liquid (outer core) or solid (inner core), seemingly without relationship to depth?

Question

Also, what is meant by liquid, viscous? Are we talking water-like liquid, oily/gelly-like for viscous?

In: Earth Science

Answer 1

The structure is due to temperature and pressure.

Essentially, below the crust is molten rock, at varying temperatures. Closer to the crust, the rock is cooler, and therefore denser and more viscous. See lava for consistency.

Further below, the rock is hotter and therefore less dense, which reduces it’s viscosity.

At the core, there is a lot of pressure generated by the weight of rock. This pressure squeezes the material tightly, and despite the high temperatures, this force is enough to force the material into a solid.