Has earth gobbled up giant craters?

Do you know that in past 3.5 billion years, over 80 asteroids - larger than the rocks that wiped out dinosaurs 66 million years ago - have bombarded earth?

But if you look around, only four of craters produced by their impacts could persist until today.

Geologists have found three such craters like the Chicxulub crater - a prehistoric impact crater buried underneath the Yucatan Peninsula in Mexico.

So where have all the craters disappeared?

"Tectonic processes, weathering and burial quickly obscure or destroy craters. If earth were not so dynamic, its surface would be heavily cratered like the Moon or Mercury," said geologists BC Johnson and TJ Bowling from department of earth, atmospheric and planetary sciences at Purdue University.

Their findings indicate that craters on earth cannot be used to understand earth's bombardment history.

According to them, layers of molten rock blasted out early in the impact process may act as better records of impacts - even after the active earth has destroyed the source craters.

"Searches for these impact ejecta layers will be more fruitful for determining how many times earth was hit by big asteroids than searches for large craters," Johnson suggested.

Till date, geologists have proof of giant craters in South Africa, and Yucatan Peninsula.

The study was published online for the journal Geology.