The Solar System Formed About 4

The solar system formed about 4.5 billion years ago. What has been the rate of bombardment by space debris in the inner part of the solar system since then?

A) There has been a relatively steady bombardment by both large and small pieces of debris since the formation.
B) The rate of bombardment was very heavy just after the solar system's creation, but the rate has decreased steadily since then.
C) The rate decreased steadily for about 400 million years after the solar system's creation. Then a very heavy bombardment began and lasted about 300 million years. The rate has been greatly reduced since then.
D) The rate has been highly erratic with no clear pattern.