(CN) – Nearly three times more asteroids have collided with the Earth and moon in the past 290 million years than ever before, a new study shows.
While the ages and numbers of craters on the moon and Earth are very similar, the study shows something else of scientific value: Earth has fewer older craters not because of erosion or tectonics, but because the impact rate on Earth was lower prior to 290 million years ago.
A team of scientists from the University of Toronto, the University of Southampton in the United Kingdom, and the Southwest Research Institute analyzed data from NASA’s Lunar Reconnaissance Orbiter to determine if fewer craters on Earth meant fewer asteroid impacts or if the loss of craters can be attributed to erosion.
One of the researchers, Thomas Gernon of the University of Southampton, has studied kimberlite pipes – extinct diamond volcanoes on Earth – that stretch up to 90 miles below the surface. These kimberlite pipes, formed over the past 650 million years, have remained relatively intact in stable terrains.
The researchers theorized that large-impact craters formed by asteroids over the same period and in the same terrains should also be preserved. This relationship helped the team understand the lack of craters formed before 290 million years ago is not because of erosion, but because there were fewer asteroid strikes before that time period – roughly the end of the Paleozoic era.
Scientists have long researched the rate that asteroids hit the Earth, but the prevailing theory was that Earth’s earliest craters have worn away due to erosion and geologic processes.
Researchers have found that moon and Earth were hit in the same proportions, but the moon is immune to the forces that have destroyed craters on Earth, such as the geologic force of plate tectonics. However, dating the craters on the moon was a challenge.
Using data on the moon’s surface temperature from NASA’s Lunar Reconnaissance Orbiter, researchers in the study identified 111 rocky craters on the moon with diameters greater than 10 kilometers with surrounding debris fields that differentiated them from the surrounding terrain. These recently exposed rocks have “high thermal inertia” and remain warm during the lunar night relative to the surrounding lunar soils (called regolith), which have low thermal inertia. The nighttime temperatures were calculated from NASA’s Diviner infrared instruments.
Using this data they compiled the ages of lunar craters older than 1 billion years. Younger craters tended to be surrounded with more boulders and rocks than older craters, due to the fact that boulders ejected by an asteroid collision are ground down over millions of years by the constant rain of meteorites.
This is where the researchers hit pay dirt: they discovered that the rate of crater formation in the last 290 million years was 2.6 times more than in the previous 700 million years, according to the study.
Scientists don’t know the reason for this jump in the impact rate, but believe it may be related to large collisions in the asteroid belt more than 290 million years ago. Such collisions create debris that can make it to Earth and the other planets of the inner solar system.
The findings have implications for the history of life on Earth, particularly as asteroid strikes have had a significant role in mass extinction events and the rapid evolution of species that follows.
"It's perhaps fair to say it was a date with destiny for the dinosaurs – their downfall was somewhat inevitable given the surge of large space rocks colliding with Earth,” Gernon said in a statement.
Other study authors included Rebecca Ghent, University of Toronto; Sara Mazrouei, University of Toronto; and William Bottke, Southwest Research Institute, Boulder, Colorado.
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