Think of the earth as an egg. The yoke is the metallic core. Here, the temperature is high enough that iron should be in a liquid state. Gravity compresses the iron to the point that it re solidifies. Surrounding the core is the mantle, an area of liquid metals that swirls around creating the Earth’s magnetic field. That’s the white of the egg. Surrounding everything is a thin shell. that is like the crust of the Earth, where we all live. Proportionally, the Earth’s crust is no thicker than the shell of an egg.
As the mantle flows around, it affects the crust above it in several ways. The shell is cracked into slabs that float above the mantle like leaves in a pond. When the slabs collide, one has to go under the other. This process creates mountains, rift valleys, even whole islands.
I’m sure you’ve seen the way that south America and Africa seem to be two puzzle pieces that lock together. 250 Million years ago, they were locked together in one large continent called Pangaea. Since then, the plates under the continents have moved away from each other at about the same speed that fingernails grow.
It wasn’t until the 1960’s that the largest formations between the plates could be seen. The Atlantic Ocean is bisected by a massive crack as the European and North American plates move away from each other. Parts of the mantle are exposed to the bottom of the ocean and solidify into new ridges. We didn’t know about the mid ocean ridge until US Navy sonar mapped the bottom after world war 2.
Plate Tectonics is the force that allows heavy metals from the interior of the planet to come to the surface. It also recycles elements as the crust reenters the mantle and melts. You could say that the Earth “Breathes” as the crust moves.