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Answer:
Explanation:
1) Most of what we know about the interior of the Earth comes from the study of seismic waves from earthquakes. ... Because the speed of the seismic waves depends on density, we can use the travel-time of seismic waves to map change in density with depth, and show that the Earth is composed of several layers.
2) denser with depth is because the rocks at this level contain iron and iron is denser than the materials at the upper layers of the mantle. The temperature of the mantle also increases with depth. ... The change in the speed of the waves at this depth indicated a difference in the density of the rock.
3) The increase in velocity of seismic waves is due to increased density existing there. It extends from the base of the crust to about 2900 km below the surface. It occupies over 80% of the earth's volume and 65% of the total mass.
4) The Earth was formed about 4.6 billion years ago. The planet was so hot that the entire Earth was molten or liquid. As the Earth cooled, the lightest materials floated to the top and the heaviest materials sank to the center. The outer part of the Earth, the crust, consists of the lightest rock.