Scientists studying geological features in southern Africa say evidence suggests a giant asteroid as big across as Rhode Island may have carved out a crater in the Earth's crust around 300 miles wide, more than double the size of the one created by the later dinosaur-killing object.
The cataclysmic event around 3.25 billion years in the past is thought responsible for geological features seen today in a region of South Africa, the Barberton greenstone belt, which holds some of the most ancient rock on Earth.
Seismic waves greater than from any recorded earthquakes would have shaken the planet for half an hour, and would have set off giant tsunamis many times higher that those following the 2011 Fukushima earthquake in Japan, the researchers said.
Traveling at 12 miles a second, the giant cosmic object, 23 miles to 36 miles across, would have caused an earthquake of 10.8 magnitude.
"We knew it was big, but we didn't know how big," says Donald Lowe, a Stanford University geologist and co-author of the published study.
Lowe, who first examined Barberton rock formations 10 years ago, says new research models have yielded an estimate of the size of the asteroid and its effects on the Earth.
The dinosaur-extinction asteroid impact of 65 million years ago off the coast of Mexico's Yucatan Peninsula, creating what is now known as the Chicxulub crater, is thought to have discharged energy a billion times greater than that of the the bombs that fell on Nagasaki and Hiroshima. The ancient impact at the center of the new research would likely have released many times more that amount of energy, the researchers say.
The atmosphere of the Earth would have experienced heating to great temperatures, while the surface water of the Earth's oceans would have been boiling, they say.
The impact was just one of a large number of huge asteroid collisions with our planet at the close of the Late Heavy Bombardment chapter early in Earth's history about 3 to 4 billion years in the past, they suggest.
While subsequent erosion has wiped out all trace of many of those impacts, a few areas in Australia and South Africa still show signs of these ancient impacts, Lowe says.
"We can't go to the impact sites. In order to better understand how big it was and its effect we need studies like this" where geological evidence allows the reconstruction of such impacts to yield clues to the bombardment of Earth during this time, he says.
