The disappearance of the dinosaurs was due to a meteorite colliding with the Earth. But about 5,000 million years ago there was a new, more violent clash.
The Earth then was not as we know it now, but a "protolur" that had half the current mass and was growing rapidly. In the same orbit around the Sun another planetite was also rotating. They had a liquid iron zone, surrounded by a rock mantle. At some point they met and collided. The blow was extremely violent, so the iron zones joined together as if they were drops of mercury.
Much of the rock broke and became satellite. To what man had preserved the iron heart and the rock satellite we have given the name Earth and Moon, respectively.