Question: what is your proof theat under the earths surface there is magma how do you know

Jon Copley answered on 22 Jun 2010:

Magma is molten rock. There has to be magma beneath the Earth’s crust, because the deeper you go into the Earth, the hotter the temperature gets (partly from the increased pressure of all the rocks on top, and partly because you are closer to the Earth’s radioactive core, which is a source of heat). We know the melting point of rock, and so we know that the temperature of the Earth must be greater than that melting point beyond a certain depth – so the rock there must be molten, i.e. magma.

We can also tell that the Earth contains a viscous layer because we can send sounds waves through the Earth, and from their behaviour (how fast they travel, and how they bounce off different layers in the Earth), we can tell that there is liquidy magma down there.

We also actually see magma escape from the interior of the Earth in volcanic features called intrusions. And because we know that the plates of the Earth’s crust move about, very slowly over millions of years (for example, North America and Europe are moving apart right now at about the rate our fingernails grow), they must be floating on something to let them move about like that. In fact, they move because they are riding convection currents in the mantle below – so the mantle can’t be made of anything solid.