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

Rain delays Vernon burning plans

Foothills prescribed burn on backburner until fall or next spring

Rain closes Vernon fields

Forecast calling for more rain Friday

VIDEO: Weekend weather for the Okanagan-Shuswap

A mix of rain, clouds and sun are expected for the Okanagan, Shuswap and Similkameen

Easter dinner at Kelowna’s Gospel Mission

Clients of the Gospel Mission are in for an Easter feast.

Dryer fire forces evacuation of CamAm Pet Treats

Fire crews are on scene of a dryer fire in Vernon

It was no Kentucky Derby: B.C. girls host foot-long snail race

Two Grade 3 students in White Rock put four snails to the test in a hotly-contested street race

40 years, 40 vendors: Vernon outdoor farmer’s market returns

The Farmer’s market will take place Monday and Thursday from 8 a.m. - 1 p.m. until the end of October

Snow falling at Big White near season’s end

Big White is open until April 22

Man airlifted to hospital after apparent hunting incident in East Kootenay

The man was in stable condition when he was flown out of Fairmont Hot Springs to a Calgary hospital

Police probe eight fires set at B.C. elementary school

Nanaimo RCMP say fires appear to have been set intentionally

Undercover cops don’t need warrant to email, text suspected child lurers: court

High court decision came Thursday in the case of Sean Patrick Mills of Newfoundland

Letter: Writer hopes Alberta will turn off the tap, teach B.C. a lesson

So glad to see Jason Kenney get elected in Alberta and hope… Continue reading

Summerland reservoirs expected to fill, despite low snow levels

Snow measurements at two Summerland sites have been significantly lower than normal

Big stories begin with small suitcase in upcoming festival

Shuswap-Okanagan storytellers to open up at Festival of Mini Theatre in Salmon Arm

Most Read