Scientists find increase in asteroid impacts on ancient Earth by studying the Moon

SwRI scientists study moon craters to understand Earth's impact history
SwRI was part of a team that used Lunar Reconnaissance Orbiter data to study the moon's craters, scaled by size and color-coded by age here, to understand the impact history of the Earth. The lunar surface is dominated by blue craters younger than 290 million years old, which is consistent with those on Earth, indicating that bombardments on both bodies has increased since that time. Credit: NASA/LRO/USGS/University of Toronto

An international team of scientists is challenging our understanding of a part of Earth's history by looking at the Moon, the most complete and accessible chronicle of the asteroid collisions that carved our solar system.

In a study published today in Science, the team shows the number of asteroid impacts on the Moon and Earth increased by two to three times starting around 290 million years ago.

"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," said lead author Sara Mazrouei, who recently earned her Ph.D. in the Department of Earth Sciences in the Faculty of Arts & Science at the University of Toronto (U of T). "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."

It had been previously assumed that most of Earth's older craters produced by asteroid impacts have been erased by erosion and other geologic processes. But the new research shows otherwise.

"The relative rarity of large craters on Earth older than 290 million years and younger than 650 million years is not because we lost the craters, but because the impact rate during that time was lower than it is now," said Rebecca Ghent, an associate professor in U of T's Department of Earth Sciences and one of the paper's co-authors. "We expect this to be of interest to anyone interested in the impact history of both Earth and the Moon, and the role that it might have played in the history of life on Earth."

SwRI scientists study moon craters to understand Earth's impact history
Dating the moon's impact craters. Credit: NASA/LRO/University of Southampton/University of Toronto

Scientists have for decades tried to understand the rate that asteroids hit Earth by using radiometric dating of the rocks around them to determine their ages. But because it was believed erosion caused some craters to disappear, it was difficult to find an accurate impact rate and determine whether it had changed over time.

A way to sidestep this problem is to examine the Moon, which is hit by asteroids in the same proportions over time as Earth. But there was no way to determine the ages of lunar craters until NASA's Lunar Reconnaissance Orbiter (LRO) started circling the Moon a decade ago and studying its surface.

"The LRO's instruments have allowed scientists to peer back in time at the forces that shaped the Moon," said Noah Petro, an LRO project scientist based at NASA Goddard Space Flight Center.

Using LRO data, the team was able to assemble a list of ages of all lunar craters younger than about a billion years. They did this by using data from LRO's Diviner instrument, a radiometer that measures the heat radiating from the Moon's surface, to monitor the rate of degradation of young craters.

During the lunar night, rocks radiate much more heat than fine-grained soil called regolith. This allows scientists to distinguish rocks from fine particles in thermal images. Ghent had previously used this information to calculate the rate at which large rocks around the Moon's young craters—ejected onto the surface during asteroid impact—break down into soil as a result of a constant rain of tiny meteorites over tens of millions of years. By applying this idea, the team was able to calculate ages for previously un-dated lunar craters.

Credit: SystemSounds

When compared to a similar timeline of Earth's craters, they found the two bodies had recorded the same history of asteroid bombardment.

"It became clear that the reason why Earth has fewer older craters on its most stable regions is because the impact rate was lower up until about 290 million years ago," said William Bottke, an asteroid expert at the Southwest Research Institute in Boulder, Colorado and another of the paper's coauthors. "The answer to Earth's impact rate was staring everyone right in the face."

The reason for the jump in the impact rate is unknown, though the researchers speculate it might be related to large collisions taking place more than 300 million years ago in the main asteroid belt between the orbits of Mars and Jupiter. Such events can create debris that can reach the inner solar system.

Ghent and her colleagues found strong supporting evidence for their findings through a collaboration with Thomas Gernon, an Earth scientist based at the University of Southampton in England who works on a terrestrial feature called kimberlite pipes. These underground pipes are long-extinct volcanoes that stretch, in a carrot shape, a couple of kilometers below the surface, and are found on some of the least eroded regions of Earth in the same places preserved impact craters are found.

"The Canadian shield hosts some of the best-preserved and best-studied of this terrain—and also some of the best-studied large impact craters," said Mazrouei.

Scientists study moon craters to understand Earth's impact history
Moon's young craters (larger than 10 kms, younger than one billion years old). Credit: Dr. A. Parker, Southwest Research Institute

Gernon showed that kimberlite pipes formed since about 650 million years ago had not experienced much erosion, indicating that the large impact craters younger than this on stable terrains must also be intact.

"This is how we know those craters represent a near-complete record," Ghent said.

While the researchers weren't the first to propose that the rate of asteroid strikes to Earth has fluctuated over the past billion years, they are the first to show it statistically and to quantify the rate.

"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 Ghent. "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.

"The question is whether the predicted change in asteroid impacts can be directly linked to events that occurred long ago on Earth."

The findings are described in the study "Earth and Moon impact flux increased at the end of the Paleozoic", published in Science.

Explore further

Lunar craters named in honor of Apollo 8

More information: S. Mazrouei el al., "Earth and Moon impact flux increased at the end of the Paleozoic," Science (2018). … 1126/science.aar4058

C. Koeberl at Natural History Museum in Vienna, Austria el al., "When Earth got pummeled," Science (2018). … 1126/science.aav8480

Journal information: Science

Citation: Scientists find increase in asteroid impacts on ancient Earth by studying the Moon (2019, January 17) retrieved 22 April 2019 from
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors

User comments

Jan 18, 2019
Yes, let's pour assumption upon assumption and then when it fits the required long age we can sit down and do some calculations.
A few insurmountable problems are
1. How did the earth form all by itself from clouds of dust.
2. How did the moon form around the earth all by itself?
3. Where did all the water on earth come from? Especially inside the mantle?
4. Where did all the water on the moon come from if there was such an almighty collision with the earth long ago with another object so that it left the moon in orbit?
5. Where did the strong magnetic field of the moon come from (given the incredible high remnant magnetic fields in moon rocks brought back?) and then disappear to ?
6. What does craters have to do with the history of life on earth if it's not possible for life to arise all by itself via random chemical and or physical processes with no outside intelligence and powerful tools?
7. Are the crater counts right, given that one impact can result in lots of craters?

Jan 18, 2019
Ups, maybe we acquired a second "dark star" (brown dwarf?) with a very large orbit some 300 million years ago. Maybe it's out there, 1 light-year away and slowly disturbing the Oort cloud.

Jan 18, 2019
Sorry G, but the recently determined orbit of 2014 MU69 (Ultima Thule) demonstrates a rather perfect circular orbit. Undisturbed for billions of years by the hypothesized Planet 9 or Planet X or close brushes with passing star systems.

That is the "real" mystery of "Frosty the Blushing Snowperson".

As for freddy's delusions of intellectual capability?
his/her/its ignorant opinions are the very definition of "pathetic joke".

Jan 18, 2019
Interesting stuff about Ultima Thule.

That 290 million yr. period is close to the galactic period of the Solar System: https://en.wikipe...tic_year

But then if the Sun had a bit of an inclined orbit going through a hypothetical dark matter disk, then there should have been 2 maxima in that period, not 1 increase.

Maybe the Sun's orbit oscillates about the galactic plane with a period of about 600 million years - a kind of resonance between oscillation and rotation? Quite unusual.

Jan 19, 2019
Makes sense, we should be in the trailing off phase of the initial bombardment and small disturbances may have huge ... um ... impact. Most likely they would be some interaction in the asteroid belt as the paper says, we do see huge collisions changing the impact record types every now and then by adding rocks from new "parent bodies".

assumptions ,,, insurmountable problems

Known and tested constraints so now translated into observations; solved problems. Don't make claims if you don't know the subject, and please provide references anyway. For example on my part, on Earth formation as solved; https://en.wikipe...physics) .

Incidentally on your trolling an ad hoc list, are you not one of those trolling science motivated by a claim that there exist religious magic? It does not, its is fact that neither 'souls' nor 'gods' exist.

Jan 19, 2019

1. How did the earth form all by itself from clouds of dust.
2. How did the moon form around the earth all by itself?

The only hope of finding answers to questions about how the Earth and Moon formed and answers to all your other questions is by studying something called SCIENCE, if only you were curious enough to bother.
We don't have ALL the details of the answers but there is much science has already answered and science is gradually giving us more and more of the answers.

You can start here:

Jan 19, 2019
Interesting stuff about Ultima Thule.

That 290 million yr. period is close to the galactic period of the Solar System:

I'm honestly surprised you didn't follow that up with a PMS for the solar system joke.

Jan 20, 2019
Makes sense

What needs to be addressed isn't so much the increase in meteor flux but chasing down the interesting correlations between the Powell's Great Unconformity, a Snow Ball Earth and the almost complete lack of craters older than 650 million years.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more