I've always thought the earth's layers were as follows:
- Crust, a few dozen KM think in most places
- Mantle, completely composed of liquid rock and molten metals, a few thousand KM thick
- Outer Core, molten iron
- Inner core, solid iron
The mantle being composed of a liquid made a lot of sense. The idea of plate tectonics floating on top of magma and bumping against each other made sense.
However, I've been told by Michael that the mantle is completely solid, which seems to not work as well with the ideas of
- Floating/moving plate tectonics
- Convection currents
If the earth's mantle is solid, why don't we say the plate tectonics are "resting on" the mantle instead of "floating on"?
How can we have convection currents through something that doesn't flow? Even if the solid rock in the mantle can why doesn't the heat just distribute itself evenly through conduction, and negate any convection tendencies?
I realize that entire books can be written on this topic, so a generalized answer is fine.