How have scientists learned about the composition of the Earths interior?
There are a number of lines of evidence that we use to deduce the nature of Earth’s interior. Since we can’t actually go down there and see for ourselves just what is down there, these lines of evidence are mostly indirect. First of all, we use the composition of surface rocks and then run a whole bunch of experiments to see what conditions will produce those compositions. We also use physics to determine what the condition are like as we go deeper beneath Earth’s surface. Given our calculations and the experiments, we have determined that the most likely composition for that which is right below the crust is the same as a rock that we call peridotite. Next we can look at Earth’s density. To get this, we need to know Earth’s mass and volume. Volume is fairly easy to measure. Mass is a little trickier. To get this we need to use Newton’s Law of universal gravitation. To put it is simple terms, you can tell how much mass a body contains by measuring how long it takes a satellite to compl
