What evidence exists today that the number of rocks and rock particle floating around in the solar system was much greater in the past soon after the planets formed?

Answer 1

The asteroid belt beyond Mars. It was formed due to the gravitational effects between Mars and the next planet outward.

Answer 2

One piece of evidence that suggests the number of rocks and rock particles in the solar system was greater in the past is the presence of asteroid families, which are groups of asteroids with similar orbits that likely originated from the breakup of a larger parent body. Additionally, the high frequency of impact craters on the moon and other planetary surfaces indicates more collisions in the past, which would have resulted from a higher density of debris in the early solar system. Astronomical observations of debris disks around young stars also support the idea of a more populated early solar system.