Into the Fire

Closer to the protosun, in the hottest regions of the forming solar system, it was the heaviest elements, not ices and gases, that survived to form the planets. Thus the terrestrial planets are rich in the elements silicon, iron, magnesium, and aluminum. The dust grains and then planetesimals from which these planets were formed were rocky rather than icy. It is fortunate that water ice and organic compounds later rained down on the early Earth, or the present-day planet would be as lifeless as the moon.