By studying meteorites we can learn what raw materials are available, and decide how we might make use of them. Again, this is more detail than I would expect on an exam. Life could not begin until the end of the Great Bombardment. Or more accurately, until the Bombardment had slowed enough for oceans and an atmosphere to form. We believe that this occurred about 4 billion years ago.
Differentiation is probably the single clearest evidence.
As mentioned in class, the large numbers of craters observed on other planets, and the lack of any rocks on Earth older than about 4 billion years also support the idea that the Earth was melted. The Moon is currently near the Earth, but has a somewhat different composition. If the Moon formed where it is, then the composition should be nearly the same as the Earth. This difference is because Mercury formed from planetismals which were near the Sun, and the heat of the sun had boiled off all the gases. Jupiter formed from planetismals which were much farther from the Sun, and did not get heated enough to boil off the gases.