There would have been a bright flash and a release of energy that some experts say would have been the equivalent of millions of nuclear bombs going off simultaneously. The dinosaurs and other creatures living in North America would have been particularly hard-hit, said Boyd.
In addition to the heat generated by the impact, things such as hot bits of glass and rock would have rained down on the dinosaurs in a matter of only a few minutes. Then fires would have broken out. The fires would have wiped out the main course for plant eaters, so they would have starved.
Once the plant eaters died out, the meat eaters would have run out of food. The planet would have been jolted into climate change. Though many scientists agree that an asteroid was, at the very least, a catalyst for the K-Pg extinction, paleontologists came up with just about every hypothesis a person could think of, because, hey, everyone is just trying to figure this thing out. Boyd said some other hypotheses included a virus, climate change, or even an influx in mammals that ate dinosaur eggs, so they eventually died out.
Believe it or not, some animals and other organisms survived the mass extinction. Crocodiles, small mammals, and even some tenacious plants, for example, managed to live on after the asteroid impact. So how did they do it? Boyd offered crocodiles as an example. All of this could have destabilized ecosystems long before and after the asteroid hit. The jolt of that impact may even have boosted the eruptions, some researchers now argue.
As more clues have emerged, some seem to conflict. He is a geoscientist at the Berkeley Geochronology Center in California. What is clear is that a massive die-off took place around 66 million years ago. It is visible in the layers of rock that mark the boundary between the Cretaceous and Paleogene periods.
Fossils that were once abundant no longer appear in rocks after that time. Studies of fossils found or not found across the boundary between these two periods — abbreviated the K-Pg boundary — show that some three out of every four plant and animal species went extinct at about the same time.
This included everything from the ferocious Tyrannosaurus rex to microscopic plankton. Over the years, scientists have blamed many suspects for this catastrophic die-out. Some have suggested global plagues struck. Or maybe a supernova fried the planet.
In , a team of researchers including father-son duo Luis and Walter Alvarez reported discovering lots of iridium in places worldwide. That element appeared along the K-Pg boundary. The finding marked the first hard evidence for a killer-asteroid impact. Piles of impact debris led crater hunters to the Caribbean. Eleven years after the Alvarez paper, scientists at last identified the smoking gun — the hidden crater. It circled the coastal Mexican town of Chicxulub Puerto. The crater actually had been discovered in the late s by oil company scientists.
Word of that find, however, did not reach crater hunters for years. Based in part on the gaping size of the depression, scientists estimated the size of the impact. They figured it must have released 10 billion times as much energy as the nuclear bomb dropped on Hiroshima, Japan, in Questions have remained, though, about how the impact might have caused so much death and destruction worldwide.
It was the darkness that followed. The ground shook. Powerful gusts roiled the atmosphere. Debris rained from the sky. Soot and dust, spewed by the impact and resulting wildfires, filled the sky.
That soot and dust then began to spread like a giant sunlight-blocking shade over the entire planet. How long did the darkness last? Some scientists had estimated that it was anywhere from a few months to years.
But a new computer model is giving researchers a better sense of what happened. It simulated the length and severity of the global cooldown. And it must have been truly dramatic, reports Clay Tabor. As a paleoclimatologist, he studies ancient climates.
And he and his colleagues have reconstructed a sort of digital crime scene. The simulation begins by estimating the climate before the smash-up. The researchers determined what that climate might be from geologic evidence of ancient plants and levels of atmospheric carbon dioxide.
Then comes the soot. A high-end estimate of soot totals some 70 billion metric tons about 77 billion U. That number is based on the size and global fallout of the impact. Global temperatures plummeted 16 degrees Celsius 30 degrees Fahrenheit. Arctic ice spread southward. Tabor shared this dramatic scenario in September in Denver, Colo. The temperature nosedived in the Pacific Ocean, around the equator.
Meanwhile, coastal Antarctica barely cooled. Inland areas generally fared worse than coastal ones. Those divides could help explain why some species and ecosystems weathered the impact while others died off, Tabor says.
Six years after the impact, sunshine returned to levels typical of conditions before the impact. Two years after that, land temperatures warmed to levels higher than had been typical before the impact. Then, all of the carbon flung into the air by the impact took effect. It acted like an insulating blanket over the planet. And the globe ultimately warmed several degrees more. Evidence of the chilling darkness is in the rock record.
Local sea surface temperatures modified lipid fat molecules in the membranes of ancient microbes. The fossilized remains of those lipids provide a temperature record, reports Johan Vellekoop. He is a geologist at the University of Leuven in Belgium. At about 93 miles wide, the Chicxulub crater seems to be the right size and age to account for the dino die-off. In , scientists drilled a rock core inside the underwater part of Chicxulub , pulling up a sample stretching deep beneath the seabed.
This rare peek inside the guts of the crater showed that the impact would have been powerful enough to send deadly amounts of vaporized rock and gases into the atmosphere, and that the effects would have persisted for years. And in , paleontologists digging in North Dakota found a treasure trove of fossils extremely close to the K-Pg boundary , essentially capturing the remains of an entire ecosystem that existed shortly before the mass extinction.
Tellingly, the fossil-bearing layers contain loads of tiny glass bits called tektites—likely blobs of melted rock kicked up by the impact that solidified in the atmosphere and then rained down over Earth.
However, other scientists maintain that the evidence for a massive meteor impact event is inconclusive, and that the more likely culprit may be Earth itself. Ancient lava flows in India known as the Deccan Traps also seem to match nicely in time with the end of the Cretaceous, with massive outpourings of lava spewing forth between 60 and 65 million years ago. Today, the resulting volcanic rock covers nearly , square miles in layers that are in places more than 6, feet thick.
Proponents of this theory point to multiple clues that suggest volcanism is a better fit. Other research has found evidence for mass die-offs much earlier than 66 million years ago, with some signs that dinosaurs in particular were already in a slow decline in the late Cretaceous.
This all makes sense, supporters say, if ongoing volcanic eruptions were the root cause of the world-wide K-Pg extinctions. Increasingly, scientists trying to unravel this prehistoric mystery are seeing room for a combination of these ideas. This nearly whole, deep-black skull belongs to the most complete specimen of Tyrannosaurus rex on display in Europe, an individual nicknamed Tristan Otto. But that notion depends a lot on more precise dating of the Deccan Traps and the Chicxulub crater.
This debate may rage for years, as scientists dig up new clues and develop new techniques for understanding the past. All rights reserved.
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