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A28 SCIENCE
Friday 18 January 2019
Asteroids are smacking Earth twice as often as before

By SETH BORENSTEIN moon as a stand-in for holes
AP Science Writer between 650 million and 1
WASHINGTON (AP) — Giant billion years old. The moon
rocks from space are falling is a good guide for estimat-
from the sky more than they ing Earth crashes, because
used to, but don't worry. it is close enough to be in
For the past 290 million the same bombardment
years, large asteroids have path and its craters last lon-
been crashing into Earth ger.
more than twice as often So what happened nearly
as they did in the previous 300 million years ago?
700 million years, accord- "Perhaps an asteroid family
ing to a new study in Thurs- was broken up in the aster-
day's journal Science . oid belt," Mazrouei specu-
But no need to cast a wary lated. The space rocks then
glance up. Asteroids still headed toward the Earth
only smack Earth on aver- and moon, and the planet
age every million or few got slightly more because it
million years, even with is a bigger target and it has
the increased crash rate. higher gravity, Ghent said.
NASA's list of potential big Outside scientists are split
space rock crashes shows about the research. Jay
no pending major threats. Melosh at Purdue said he
The biggest known risk is a found the number of cra-
4,200-foot (1.3-km) wide This Dec. 29, 1968 photo made available by NASA shows the large moon crater Goclenius, fore- ters too small to come to a
asteroid with a 99.988 per- ground, approximately 40 statute miles in diameter, and three clustered craters Magelhaens, reasonable conclusion, but
cent chance that it will miss Magelhaens A, and Colombo A, during the Apollo 8 mission. Harvard's Avi Loeb said the
Earth when it whizzes very Associated Press case was convincing.
near here in 861 years. Humans might not have
Tell that to the dinosaurs. it." ters that were no older than be seen brings the total to emerged without mass ex-
Most scientists think dino- Mazrouei and colleagues 290 million years and nine about 260 space crashes tinctions from space rocks
saurs and a lot of other in the United Kingdom and between 291 million years on Earth in the last 290 mil- about 250 million and 65
species went extinct after a United States compiled a and 650 million years old. lion years. Adding in other million years ago, Loeb
huge space rock crashed list of impact craters on But we can see relatively factors, the science team said in an email, adding,
into Central America about Earth and the moon that few big craters on Earth determined that the cur- "but this enhanced impact
65 million years ago. were larger than 12 miles because the planet is more rent space crash rate is 2.6 rate poses a threat for the
"It's just a game of probabil- (20 km) wide and came than 70 percent ocean and times more than the previ- next mass extinction event,
ities," said study lead author up with the dates of them. past glaciers smoothed out ous 700 million years. which we should watch for
Sara Mazrouei, a University It takes a space rock that's some holes, said University Craters older than 650 mil- and attempt to avoid with
of Toronto planetary scien- half a mile (800 meters) of Toronto planetary sci- lion years are mostly wiped the aid of technology."
tist. "These events are still wide to create holes that entist Rebecca Ghent, a off on Earth by glacial forc- "This demonstrates how ar-
rare and far between that big. study co-author. es so the scientists used im- bitrary and fragile human
I'm not too worried about The team counted 29 cra- Extrapolating for what can't pact craters on the nearby life is," Loeb wrote.q

Hawaii’s humpback whales to be

counted despite fed shutdown

KAILUA-KONA, Hawaii (AP) tuary Foundation is a non- the foundation’s president
— An annual humpback profit partner of the Na- and CEO.
whale count in Hawaii will tional Marine Sanctuary “Unfortunately, critical
take place despite the System. sanctuary research that
federal government shut- Although removed from could help us understand
down. the endangered species these changes is on hold
In this Jan. 23, 2005 file photo, a humpback whale leaps out of West Hawaii Today report- list in 2016, most humpback indefinitely due to the gov-
the water in the channel off the town of Lahaina on the island of ed Friday that volunteers whales remain a federally ernment shutdown.”
Maui in Hawaii. from the National Marine protected species. Each year, about 11,000
Associated Press Sanctuary Foundation will Over 300 volunteers are humpback whales migrate
coordinate this season’s expected to count whales from Alaska to Hawaii
Ocean Count, a commu- from shore on Jan. 26. where they mate and give
nity citizen science proj- Researchers say there has birth during the winter.
ect that occurs during the been an estimated 50 to 80 Ongoing speculation and
peak of whale season. percent drop in humpback theories have developed
The survey is usually con- whale sightings in recent about the sudden decline
ducted by the National years. in the whale population’s
Oceanic and Atmospheric “Fewer humpback whales presence in Hawaii. In No-
Administration’s Hawaiian are being observed in the vember, a group of whale
Islands Humpback Whale main Hawaiian Islands in experts met in Honolulu to
National Marine Sanctuary. recent years, and we don’t better understand the sud-
The National Marine Sanc- know why,” said Kris Sarri, den decrease.q