Large asteroids have been crashing into Earth more than twice as frequent over the past 290 million years, researchers of a new study published in the journal Science reported.
University of Toronto planetary scientist Sara Mazrouei and colleagues spotted the trend after studying impact craters on Earth and on the moon that were larger than 12 miles. It takes space rocks measuring at least half a mile wide to produce holes this size.
Dating Asteroid Impacts
One problem with tracing the history of asteroid strikes on Earth is that erosion and geological processes may have wiped out traces of our planet's oldest impact craters. It turns out, however, that scientists can still learn about Earth's impact history by studying craters on the moon.
Because of their close proximity to each other, the Earth and its natural satellite have experienced similar rates of asteroid strikes over time. The moon, however, is not subject to erosional processes that gradually destroy craters on Earth. Thus, it has retained a long-term record of impact history.
If scientists can date these lunar craters, it is also possible for them to recreate the history of asteroid strikes on Earth and the rates of the bombardments.
They did this with the help of NASA's Lunar Reconnaissance Orbiter (LRO). The scientists managed to date the lunar craters using thermal data and images of the moon collected by the LRO.
Uptick In Asteroid Strikes
The scientists found the ages and numbers of craters on the moon and on Earth are extremely similar, challenging the idea Earth has lost many early craters.
They also found the impact rate on Earth increased between two and three times about 290 million years ago, just before the dinosaurs emerged.
"This means that the Earth has fewer older craters on its most stable regions not because of erosion, but because the impact rate was lower prior to 290 million years ago," said William Bottke, from Southwest Research Institute in Boulder, Colorado.
Is Earth Likely To Be Hit By An Asteroid?
NASA lists potentially dangerous asteroids. So far, it has not found a space rock that poses a catastrophic threat in the near future. Researchers also said they are not worried despite the increased frequency of asteroid impacts because these do not occur frequently.
"It's just a game of probabilities," Mazrouei said. "These events are still rare and far between that I'm not too worried about it."