At the Beginning of the Solar System's History, a Ready

Multiple Choice

At the beginning of the solar system's history, a ready supply of proto-planets or mini-planets crashed into the developing planets and each other - something astronomers call the "era of giant impacts." How long do astronomers estimate this era lasted?

A) only a few dozen years - it was over very quickly
B) about 100 million years (0.1 billion)
C) about two billion years
D) about four billion years (it only ended about half a billion years ago)
E) that era is not finished yet - giant impacts are still happening all over the solar system