How are scientist able to study the composition and size of the interior layers of earth?

Answer 1

They use seismic waves. If not produced by a natural event like a earthquake, scientists(geophysicists generally) will create a explosion on land or on water. By using a seismograph, scientist are able to track how the seismic wave travels underground. Scientist already know that some earth materials cause waves to travel at a general velocity. For example, waves travel at a speed of

1.5km/s in water

2km/s in sediments

5.07km/s in basalts

6.69km/s in gabbro

8.13km/s in peridotite

There is more materials they know the speed of I just can't remember them :P so if a wave is traveling at 1 of these speeds you know you got gabbro or whatever.

However, scientist don't know the velocities of the waves but they can figure them out by studying refracted and reflected waves(refracted is more commonly studied to determine velocities). Refracted happens if layer 2 has a greater velocity than layer 1 and reflected happens if layer 1 has a greater velocity than layer 2.

Once they know the velocities they can determine how big a layer is.

They figure out the velocities as well as how big a layer is by using math. For example they can figure out the height of a layer by the formula t*V1/2costhetax

Where t is travel time

V1 and V2 is the velocity of the first layer and second layer

And thetax is equal to arcsin(v1/v2)

And if you don't know the travel time then there is whole different formula that can be used

Basically a lot of math is used to determine the size of layers.

What I just described was very generalized there is a whole lot more to it but way too complicated to explain