Instead it is differentiated . Some of these pieces stuck together. The resulting piece had more mass and hence attracted other pieces of matter with a stronger gravitational force. These other pieces also smacked into the proto-Earth and relesed energy. Radioactive energy from some heavy elements.
Radioactive elements are unstable and break apart into pieces releasing energy in the process.
So let's go back to our map of earthquakes around Earth. In the mid 1960's the theory of plate tectonics suggested that these slabs or plates are actually slowly moving, drifting along the surface of Earth. This process called continental drift , actually shapes the Earth's surface, continents, mountain ranges, etc. Notice that the plates do not match the continents. Some plates are drifting apart.