BOULDER — Massive asteroids may have pummeled Earth for about 2 billion years longer than previously thought, according to a research team that includes scientists from the Southwest Research Institute in Boulder.
Many researchers believe there was a period from 4.1 billion years ago to 3.8 billion years ago known as the Late Heavy Bombardment when the moon and the Earth were barraged by a large number of asteroids.
The evidence of the Late Heavy Bombardment is largely etched on the face of the moon, where impact craters do not erode or get covered under layers of newer rock and soil as they do on Earth.
“The Earth is very good at getting rid of things, or just burying things,” said SWRI scientist William Bottke.
The last large-impact crater on the moon, called Orientale, is thought to be about 3.8 billion years old, and many scientists believe it marked the end of the Late Heavy Bombardment.
But the new study, published in the journal Nature, shows that asteroids may have continued to shower Earth until about 1.8 billion years ago — a time when life was struggling to gain a foothold on the planet.
“The last really big impacts on the moon were about (3.8 billion years ago), so we just assumed that big impacts on the Earth ended at the same time,” Bottke said.
But for the new study, scientists built on existing models of what the universe may have looked like billions of years ago, especially the Nice model, named after the observatory where it was developed in Nice, France.
The result is that the scientists believe the tail end of the Late Heavy Bombardment may have stretched out much longer than previously thought.
In fact, the researchers believe that as many as 70 asteroids — all of them as large or larger than the one blamed for killing off the dinosaurs — may have struck Earth after the Late Heavy Bombardment was thought to have ended.
