«The Earth was assembled from a lot of heterogeneous material from the solar system,» Valley explains, noting that the early Earth experienced intense bombardment by meteors, including a collision with a Mars - sized object about 4.5 billion years ago «that formed our moon, and melted and homogenized the Earth. (sciencedaily.com)
This was a time of intense bombardment for the planets as they scooped up matter and debris left around from the nebula that formed them. (solarviews.com)
As far as habitability goes, the researchers themselves point out another problem: due to the massive debris disk surrounding tau Ceti, the outer two planets are likely subject to intense bombardment via comets and asteroids, which would pose obvious issues for life. (gizmodo.com)