How do we know the makeup of the internal part of the earth?

Question

My friend was telling me the conjecture is based on what we think rock and metal under pressure would do, and the theory of liquid parts inside is confirmed by certain waves set up by earth quakes where some can pass through solid but not liquid or vice versa. My question is, how do we know the liquid that's interupting the wave or slowing it down or whatever is the liquid rock, and not the underground reservoirs wells are dug into?

I have no science background so use every day terms to explain jargon, please. Thanks.

Answer 1

Ok so you've heard all about the geophysics and wave propegation for densities an all that. So to make it short, the liquid we see is very dense, density affects refraction, so water would refract differently than rock. Its the same as when you put a stick into the water and the end thats wet doesn't look like it attaches to the dry part. Light wave are refracted the same as seismic waves. Different material refracts waves differently

You said that there is a conjecture about what materials do at depth. This has been true until recently. Check out something called the diamond anvil cell. We can now see what rocks do at depth by crushing them between two clear diamonds to pressures up to that of the core. All the while watching the metamorphisms through a tiny camera. Changes that were thought to take millions of years happen instantly in some cases.

Answer 2

I'll try to keep this as jargon free as possible.

Basically, we can tell that the Earth's centre isn't entirely solid because of irregularities in the Earth's orbit - due to the fact that when it spins, it becomes oblate - distorted, kinda pear shaped really because of the movement of liquid inside. There's also the fact that the earth's surface isn't one big mass but made up of smaller plates with lava coming up - the Earth's crust is essentially floating on the lava. Where there are weaknesses in the crust, and the heat builds in a pocket, a volcano can errupt - that's how we have volcanos

http://en.wikipedia.org/wiki/Earth#Internal_structure

Basically, if you imagine the Earth as a chocolate shell with creamy filling and a nut in the middle, this is what we can prove with science.

http://www.sciencedaily.com/releases/1998/12/981211083655.htm

Answer 3

It is in fact based on the deflection of waves generated by earthquakes (as detected by multiple seismometers around the globe). Just like any other type of wave (sound, light, water) some materials deflect them more than others. This has much to do with the density of the material through which the waves propagate.

This site should give you more detail.