How have scientists been able to determine the composition of earth’s layers?

I believe scientists have been able to determine the composition of the Earth's layers through seismic waves.  Hope this helped!

-TTL

The correct answer is with the help of seismic waves.

Explanation:

The majority of what we know about the interior of the Earth is mainly because of the seismic waves. These are the waves of energy, which can be a result of earthquakes. The two prime kinds of seismic waves are the surface waves and the body waves.  

The surface waves move only along the Earth's surface, while the body waves move through the interior of the Earth in all the directions. It is the body waves behavior, which has provided the clues to the scientists regarding the composition of the Earth's layers. There are two kinds of body waves, these are the primary and the secondary waves.  

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.