Moon's craters reveal recent spike in outer space impacts on Earth.

Moon's craters reveal recent spike in outer  space impacts on Earth

It has long been thought that as the solar system grows older and stodgier, the number of comets colliding of earth and other planets has steadily gone down. But a new study reveals what appears to be a dramatic 2.5 times increase in the number of impacts striking  earth in the past 300 millions years.

Earth's surface is dotted with impact craters from the past billions years, but old craters are rarer than younger ones, a bias attributed to the crust - eating churn of plate tectonics, volcanic and erosion. But  looking at the moon which doesn't deal with the same forces but faces the same bombardment can probe the past of both bodies.

Earth's surface is dotted with impact craters from the past billions years, but old craters are rarer than younger ones, a bias attributed to the crust - eating churn of plate tectonics, volcanic and erosion. But  looking at the moon which doesn't deal with the same forces but faces the same bombardment can probe the past of both bodies. 

But scientist still don't know what caused the uptick. Perhaps several large asteroids collided or otherwise broke up some 300 million years ago, their chunks slowly migrating out from the asteroid belt to bombard Earth, the researchers say. And that could have included the giant impact, 66 million years ago that wiped out most of the dinosaurs.