Asteroid that wiped out dinosaurs hit Northern Hemisphere hardest

Springtime meteorite strike proved devastating for species rearing their young

Three-quarters of species were wiped out, including the dinosaurs, following the asteroid strike 66 million years ago. Image: Joschua Knüppe

Some species in the Southern Hemisphere survived the asteroid strike that wiped out the dinosaurs 66 million years ago because they were hibernating or buried underground to escape cold weather, researchers believe.

The Chicxulub asteroid hit what is now the Yucatan Peninsula in Mexico during springtime in the north, a catastrophic event that wiped out 76 per cent of all species including dinosaurs and ammonites, according to a new study in the journal Nature.

The timing of the strike had a profound effect on animal populations as the Northern Hemisphere was hit at a crucial period in the breeding cycle, researchers said.

Ecosystems in the Southern Hemisphere, where it was autumn, recovered up to twice as fast compared with the north, where animals were on the surface foraging for food, reproducing and rearing their young.

Researchers believe that some birds and crocodile species in the Southern Hemisphere survived the impact of the 12-kilometre-wide asteroid and the resulting nuclear winter and were able to spread to other parts of the world.

“If you were on the surface when the meteorite strikes, you were likely to be killed,” said Melanie During, of Uppsala University in Sweden, one of the authors of the paper. “The reign of the dinosaurs ended in spring.”

The immediate impact of the meteorite strike was felt up to 3,500 kilometres away and included tsunamis and large-scale forest fires.

Slivers of molten rock were blasted into space by the impact of the asteroid before crystallising and raining back to Earth as deadly glassy bullets.

Researchers studied the remains of filter-feeding sturgeon and paddlefish in North Dakota, United States, that died within an hour of the asteroid strike after the shards clogged their gills during a river surge.

A paddlefish discovered in North Dakota that was killed within an hour of the asteroid strike 66 million years ago. Photo: European Synchrotron Radiation Facility

“This deposit literally looks like a car crash frozen in place. It looks like the most violent thing I have seen preserved in pristine conditions,” Ms During said.

Researchers from Sweden, the Netherlands, UK, France and Belgium used carbon dating and analysed bone growth patterns of the fish to conclude that the asteroid hit around April, when springtime temperatures were similar to today.

“To be able to fight the nuclear winter you first need to survive the actual impact,” Ms During said.

“If hibernating, that increased your chances. If you sealed yourself in a burrow or sheltered underwater, that could help you. Anybody in the Southern Hemisphere already sheltering had a much better chance of surviving.”

The mass extinction was likely to have unfolded over several thousand years, with rapid climate change triggered by the meteorite strike.