Research suggests that an asteroid impact was disastrous for the dinosaurs, but the strike season may have increased extinction rates for other species.
Scientists have found evidence that the devastating impact 66 million years ago, which wiped out three-quarters of Earth’s species and created the Chicxulub crater in modern Mexico, occurred in spring in the northern hemisphere.
The timing meant that many animals north of the equator were especially vulnerable to the intense heat wave unleashed by the collision, having just emerged from the harsh winter months. Other animals in the south might have done better given that it was fall, especially if they roamed burrows.
The direct hit from the asteroid caused an intense global heat wave that proved fatal to many exposed animals. In the aftermath, temperatures are thought to have dropped so severely in the nuclear winter that many species were driven to extinction.
“To be able to fight off that nuclear winter, you first had to survive the actual impact,” said Melanie While, a paleontologist at Uppsala University in Sweden. “Anything in the Southern Hemisphere that is already harboring has a better chance of surviving.”
When the asteroid collided, it blasted molten rock into space, which crystallized and rained back to Earth as “collision pellets” on the same day. Scientists have found some of these pellets lodged in the gills of fossilized paddlefish and sturgeon excavated from a fossil site called Tanis in North Dakota.
The discovery of more balls around the fossils indicates that the glass particles were still flocculent when the fish perished, linking the time of death to the day, and possibly even the hour, of the collision. The fish appears to have died when buried alive due to the sediment that shook in the impact.
Writing in a nature magazineIn this article, the scientists describe how they determined seasonal cycles in the growth rates of fish bones, along with changes in carbon isotopes associated with seasonal changes in the abundance of zooplankton, a staple food for fish. All results point to the death of fish – and thus the asteroid impact – in the spring. separate search Regarding the fossils published by Professor Philip Manning at the University of Manchester in December, he came to a similar conclusion.
It is unclear whether the small animals in the northern hemisphere are actually worse off than those in the southern. There is evidence for this, said Denis Foyten, a co-author on the latest study at Uppsala University Northern hemisphere turtles They were wiped out in an asteroid strike, after which the turtles from the south repopulated their habitats.
Dr Daniel Field, assistant professor of vertebrate palaeontology at the University of Cambridge, who was not involved in the research, said it was “reasonable” that the disaster would have affected the fauna of the northern hemisphere more.
“If the asteroid hit a biological hotspot of the year for many organisms in the northern hemisphere, it may have contributed to extinction rates that would have been higher than would otherwise be expected,” he said.
But he added that there was nothing much bigger than a domestic cat that survived an asteroid impact and that many species could have collapsed each time they hit. “It is possible that the large, non-avian dinosaurs would have become extinct no matter what time of year the asteroid impacted,” he said.