How do people know the earth's physical make-up if they've only dug 12 km?

Question

People have dug only 12km into the ground, yet they know what happens beneath. How do they know this?

Answer 1

It's a very well-educated guess. Let me explain...

We know that there must be magma under the earths crust, because we see it coming from volcanoes... it can't come from anywhere else.

We know how far down the magma goes, and that there is a solid core, from a variety of tests.

When an earthquake happens, the waves can be detected on the other side of the world... however, it is not directly across the globe, as you would expect. it is deflected in a strange way. scientific tests have shown that the only way this can happen is if there is a layer of liquid above a solid core... it does get a little bit complicated.

Also, the moment of inertia and density of earth can be calculated. Scientists have used these numbers to calculate a variety of things, but even I don't entirely understand how this works... I almost failed the unit on moment of inertia.

Scientists know that the core is iron and nickel, because of the magnetic field of the earth, and the density. Moving, hot iron creates a magnetic field... that is one of it's properties.

We also know about tectonic plates because we can actually witness, and measure, continental drift.

This is a bit of an amateur explanation, but I hope it helps nonetheless. maybe wikipedia can help you more.

http://en.wikipedia.org/wiki/Earth's_core

Answer 2

Oooh, oooh, I just learned about this one in class! My teacher told me that they actually use seismic waves. Different types of waves go through different things. They wait for the waves to come back after they put them into the ground. Then they can make a guess. All the waves also change direction when they meet different stuff (I guess like liquid or rock or whatever) so that helps too

Answer 3

Yeah... powerful seismograph, seismic equipments, heat and light wave equipments and BIG BIG BIG SPECULATIONS AND GUESS!!!

How do I know... stupid useless geology classes.