Asteroids are smacking Earth twice as often as before

The team counted 29 craters that were no older than 290 million years

Giant rocks from space are falling from the sky more than they used to, but don’t worry.

For the past 290 million years, large asteroids have been crashing into Earth more than twice as often as they did in the previous 700 million years, according to a new study in Thursday’s journal Science .

But no need to cast a wary glance up. Asteroids still only smack Earth on average every million or few million years, even with the increased crash rate. NASA’s list of potential big space rock crashes shows no pending major threats. The biggest known risk is a 4,200-foot (1.3-km) wide asteroid with a 99.988 per cent chance that it will miss Earth when it whizzes very near here in 861 years.

Tell that to the dinosaurs. Most scientists think dinosaurs and a lot of other species went extinct after a huge space rock crashed into Central America about 65 million years ago.

“It’s just a game of probabilities,” said study lead author Sara Mazrouei, a University of Toronto planetary scientist. “These events are still rare and far between that I’m not too worried about it.”

Mazrouei and colleagues in the United Kingdom and United States compiled a list of impact craters on Earth and the moon that were larger than 12 miles (20 km) wide and came up with the dates of them. It takes a space rock that’s half a mile (800 metres) wide to create holes that big.

The team counted 29 craters that were no older than 290 million years and nine between 291 million years and 650 million years old.

But we can see relatively few big craters on Earth because the planet is more than 70 per cent ocean and past glaciers smoothed out some holes, said University of Toronto planetary scientist Rebecca Ghent, a study co-author.

Extrapolating for what can’t be seen brings the total to about 260 space crashes on Earth in the last 290 million years. Adding in other factors, the science team determined that the current space crash rate is 2.6 times more than the previous 700 million years.

Craters older than 650 million years are mostly wiped off on Earth by glacial forces so the scientists used impact craters on the nearby moon as a stand-in for holes between 650 million and 1 billion years old. The moon is a good guide for estimating Earth crashes, because it is close enough to be in the same bombardment path and its craters last longer.

READ MORE: Cigar-shaped interstellar object could be alien probe, says Harvard study

So what happened nearly 300 million years ago?

“Perhaps an asteroid family was broken up in the asteroid belt,” Mazrouei speculated. The space rocks then headed toward the Earth and moon, and the planet got slightly more because it is a bigger target and it has higher gravity, Ghent said.

Outside scientists are split about the research. Jay Melosh at Purdue said he found the number of craters too small to come to a reasonable conclusion, but Harvard’s Avi Loeb said the case was convincing.

Humans might not have emerged without mass extinctions from space rocks about 250 million and 65 million years ago, Loeb said in an email, adding, “but this enhanced impact rate poses a threat for the next mass extinction event, which we should watch for and attempt to avoid with the aid of technology.”

“This demonstrates how arbitrary and fragile human life is,” Loeb wrote.

___

The Associated Press Health & Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.

Seth Borenstein, The Associated Press


Like us on Facebook and follow us on Twitter.

Just Posted

Island residents team up on beach cleanups, call for government regulation

‘It’s way beyond what we can deal with’: Lasqueti, Texada, Denman islanders

‘A really kind person’: Parksville’s Nick Major remembered by instructor

Outpouring of support in the days following death of young man

Banners could add pop of colour to Parksville business district

District includes businesses between the Orange Bridge and McVickers Street

Last call for the ever-vanishing payphone in Parksville Qualicum Beach

Where many phones once resided, only memories remain

Developers go back to drawing board after high-rise application deferred by Parksville council

IAG Developments has proposed a multi-building development on city’s waterfront

Rich the Vegan scoots across Canada for the animals

Rich Adams is riding his push scooter across Canada to bring awareness to the dog meat trade in Asia

Canadian high school science courses behind on climate change, says UBC study

Researchers found performance on key areas varies by province and territory

Six inducted into BC Hockey Hall of Fame

The 26th ceremony in Penticton welcomed powerful figures both from on and off the ice

RCMP investigate two shootings in the Lower Mainland

Incidents happened in Surrey, with a victim being treated at Langley Memorial Hospital

CRA program to help poor file taxes yields noticeable bump in people helped

Extra money allows volunteer-driven clinics to operate year-round

Recall: Certain Pacific oysters may pose threat of paralytic shellfish poisoning

Consumers urged to either return affected packages or throw them out

How a Kamloops-born man helped put us on the moon

Jim Chamberlin did troubleshooting for the Apollo program, which led to its success

Sexual harassment complaints soaring amid ‘frat boy culture’ in Canada’s airline industry

‘It’s a #MeToo dumpster fire…and it’s exhausting for survivors’

Most Read