Back when our planet was an awkward teenager, during that long stretch of time when creatures started to invade the land, asteroid strikes were few and far between – then something changed.
New research published in Science this week shows that we are currently in the midst of a period where asteroid strikes are freakishly high. Over the past 290 million years, the number of asteroid impacts on Earth appears to have increased threefold compared to the previous 710 million years.
"Our research provides evidence for a dramatic change in the rate of asteroid impacts on both Earth and the Moon that occurred around the end of the Paleozoic era," lead author Sara Mazrouei of the University of Toronto (UT) said in a statement.
"The implication is that since that time we have been in a period of relatively high rate of asteroid impacts that is 2.6 times higher than it was prior to 290 million years ago."
Meaning instead of an average strike that left a crater around 10 kilometers wide (6. miles) impacting once every 3 million years, they now occur once every 1 million years.
Scientists had noticed a scarcity of impact craters on Earth older than 290 million years, but had assumed they had simply been wiped off the geological record by years of erosion. So, the team turned to our closest ally, the Moon, as a proxy.
The Earth and Moon have been struck by asteroids a relatively similar amount throughout their long-standing relationship, making our satellite the most accessible chronicle we have of the asteroid collisions that helped shape the young Solar System. This new study saw scientists quantify the rate of asteroids collisions on the Moon using images and thermal data collected by NASA’s Lunar Reconnaissance Orbiter (LRO).
“It was a painstaking task, at first, to look through all of these data and map the craters out without knowing whether we would get anywhere or not,” Mazrouei admitted.
Nevertheless, their hard work paid off. The findings suggest that Earth has fewer older craters because the impact rate was lower, not because of erosion. It remains unclear why Earth (and the Moon) became such a hotspot for asteroids 290 million years ago, but the researchers speculate it could be to do with the goings-on inside the asteroid belt between the orbits of Mars and Jupiter. If this asteroid belt experienced some major collisions some 300 million years ago, then it would fling more debris into our neck of the woods.
"The findings may also have implications for the history of life on Earth, which is punctuated by extinction events and rapid evolution of new species," said co-author Rebecca Ghent, an associate professor at UT. "Though the forces driving these events are complicated and may include other geologic causes, such as large volcanic eruptions, combined with biological factors, asteroid impacts have surely played a role in this ongoing saga."