The dinosaurs may have already been going extinct before the cataclysmic space rock hit Earth, new findings suggest

dinosaur asteroid meteor
An artist’s depiction of the moment the Chicxulub asteroid struck present-day Mexico 66 million years ago.

It’s tempting to ponder what life on Earth might have looked like had a space rock not hit 66 million years ago. That impact in present-day Mexico doomed the dinosaurs and a majority of land and marine species. In its absence, would humans and other mammals have eventually duked it out with T. rex and triceratops?

The answer is probably not, according to a study published Tuesday.

That research found that six major groups of dinosaurs were slowly going extinct over the 10 million years prior to the crash. The impact’s consequences – mile-high tsunamis, raging fires, and a choking cloud of thick dust and sulfur that blotted out the sun – were merely a nail in the dinosaurs’ coffin.

“The meteorite is seen as a coup de grâce for dinosaurs, which finished them off,” Fabien Condamine, a research scientist at the University of Montpellier in France who co-authored the new study, told Insider.

Condamine and his collaborators suggest that a period of global cooling may have contributed to a decline in the overall number of dinosaur species, which then made it impossible for the animals to recover after the cataclysmic event.

“Many paleontologists think dinosaurs would have continued to live if the asteroid did not hit Earth. Our study brings new information for this question, and it seems that dinosaurs were not in good shape before the impact,” Condamine said.

Dinosaurs were already on their way out

T. rex
A full-grown Tyrannosaurus rex weighed between 6 and 9 tons and was up to 43 feet long.

The researchers behind the new study looked at 1,600 fossils from 247 dinosaur species that lived during the late Cretaceous period – from about 100 million to 66 million years ago. That group includes two-legged carnivores like the T. rex, triceratops, and duck-billed dinosaurs.

The team grouped them into six large families, then analyzed how the diversity of species in those families changed over time. The results show that across all six groups, the number of species started to gradually decline 76 million years ago, prior to the space-rock impact.

“We do not find that dinosaur diversity was high and diversifying toward the end of the Cretaceous, as previously thought,” Condamine said.

His isn’t the first group of scientists to suggest that dinosaurs actually went extinct gradually. A 2016 study found that as species of dinosaurs that had been around on Earth a while went extinct, no newer species replaced them. Although questions lingered as to whether that conclusion was simply the product of an incomplete fossil record, this new study shows that older species did indeed have higher extinction rates than younger ones.

An herbivore monopoly

Arctic dinosaur hadrosaur
A painting of Ugrunaaluk kuukpikensis, a species of duck-billed dinosaur that lived during the Cretaceous period.

In the late Cretaceous period, the planet began to cool: Starting 80 million years ago, global temperatures dropped by about 13 degrees Fahrenheit (7 degrees Celsius).

Given that dinosaurs relied on the temperature of their environment to regulate their body heat, Condamine said, that change in climate might have played a role in their extinction rates.

“Warm periods favored dinosaur diversification whereas cooler periods led to enhanced extinctions,” the study authors wrote.

Another possible explanation for the dinosaurs’ decline is a change in the number of herbivore species in the ecosystem. Hadrosaurs, or duck-billed herbivores, seem to have dominated between 76 million and 66 million years ago – out-competing their fellow leaf-eaters like triceratops and the clubbed-tailed, armored ankylosaurs. That contributed to the decline of those other herbivores.

“Removing herbivores can make the entire ecosystems more prone to extinction cascades,” Condamine said.

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A second space rock hit Earth after the one that doomed the dinosaurs – a nail in the coffin of the mass extinction

dinosaur asteroid meteor
An artist’s depiction of the moment the Chicxulub asteroid struck in present-day Mexico 66 million years ago.

About 66 million years ago, Earth took a one-two punch, according to a new study.

First came a space rock 6-miles-wide that struck present-day Mexico. The impactor, named Chicxulub, contributed to the demise of the dinosaurs, along with 50% to 75% of life on Earth.

Then, 650,000 years later, a mile-sized asteroid known as Boltysh struck. The rock carved out a 15-mile-wide crater into what is now central Ukraine.

Scientists once thought both Boltysh and Chicxulub contributed to the mass extinction that doomed the dinosaurs. But according to the study published Friday in the journal Science Advances, Boltysh likely impacted Earth long after the last victims of the extinction died out.

“I believe the extinction was essentially done and dusted” by the time Boltysh hit, Annemarie Pickersgill, a researcher at the University of Glasgow who specializes in meteorite impacts and co-author of the new study, told Insider.

While it’s unlikely Boltysh exacerbated the die-off, Pickersgill said the second impact may have delayed Earth’s recovery from the catastrophic extinction.

Analyzing rocks that melted during the Boltysh impact

melt rock from boltysh impact site ukraine
A piece of shocked quartz from the Boltysh impact crater in the Ukraine.

Scientists discovered the Boltysh impact in 2002, and an initial study suggested the asteroid had hit 2,000 to 5,000 years before Chicxulub did.

Pickersgill said that her team had intended to date the Boltysh crater with more precision, but she didn’t expect their findings to upend previous research.

“I was surprised to find that the age for Boltysh was after​ Chicxulub,” she said.

The researchers first analyzed two samples from deep within the crater, more than one-third of a mile underground. The heat from the asteroid impact had melted the rocks, so dating them allowed Pickersgill to piece together when Boltysh hit.

Then, the team looked at samples from a layer of sediment in Montana that coincided with the Chicxulub impact. Using radiometric dating – a technique that determines how long it takes for radioactive material in the rocks to decay – the team determined the Boltysh rocks melted about 650,000 years after Chicxulub struck.

Boltysh may have contributed to a burst of global warming

Chicxulub_impact asteroid
This painting depicts an asteroid slamming into tropical, shallow seas of the sulfur-rich Yucatan Peninsula in what is today southeast Mexico. The aftermath of this immense asteroid collision, which occurred approximately 65 million years ago, is believed to have caused the extinction of the dinosaurs and many other species on Earth.

The updated age for the Boltysh crater coincides with a period of intense global warming known as the lower C29 hyperthermal, the study authors said.

During a hyperthermal event, which can last up to 40,000 years, average global temperatures can increase by 5.4 degrees Fahrenheit (3 degrees Celsius).

Pickersgill’s team hasn’t determined yet whether the asteroid caused the hyperthermal.

But she said there is evidence that suggests Chicxulub first cooled the Earth’s climate, then warmed it.

When the dino-killing rock hit, it kicked up a cloud of dust, sulfur, and carbon dioxide into the atmosphere. That gaseous haze blocked the sun for a couple of decades, one study suggests, cooling the Earth.

During those few decades, most of Earth’s land and marine species went extinct.

Eventually, the Chicxulub cloud dissipated and the remaining sulfur and carbon in the atmosphere – which trap heat on Earth’s surface – started warming the planet.

But once Boltysh hit, that impact may have released additional gases into the air and exacerbated that warming. This could’ve made it more difficult for Earth’s species to recover following the mass extinction.

Research suggests it took 9 million years for the number of different species in North America to return to pre-Chicxulub levels.

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How a 14-year-old picked up a piece of fossil almost 20 years ago and jumpstarted the beginning of dinosaur discovery in Australia

Dr. Scott Hocknull and Robyn Mackenzie pose with a 3D reconstruction and the humerus bone of "Cooper," a new species of dinosaur discovered in Queensland and recognized as the largest ever found in Australia.
Dr. Scott Hocknull and Robyn Mackenzie pose with a 3D reconstruction and the humerus bone of “Cooper,” a new species of dinosaur discovered in Queensland and recognized as the largest ever found in Australia.

  • One of the 15 largest dinosaurs in the world was discovered in Australia.
  • The discovery comes less than 20 years since the country first began finding dinosaur fossils.
  • Australia was believed to not have any before a 14-year-old found a piece in 2004.
  • Visit Insider’s homepage for more stories.

Less than 20 years before “the southern titan” became the largest dinosaur discovered in Australia, a 14-year-old boy picked up a piece of fossil that would begin the hunt for the extinct creatures on the continent.

Robyn Mackenzie, Director of the Eromanga Natural History Museum, which houses the dinosaur, told Insider the discoveries began after her son, Sandy, found an unusual rock on the family property in the outback of Queensland.

“And as it turned out, this was the very … beginning of the discoveries of dinosaurs in a really large part of outback Australia, where previously they’d never been discovered before and it wasn’t even a belief that they would have been preserved in that area because of weather,” Mackenzie said.

Not long after that discovery, a team dug up the skeleton of what would be the Australotitan cooperensis, or “southern titan,” in 2007. It would take another 14 years to officially identify and describe the dinosaur to find it was among the top 15 largest in the world.

Mackenzie told Insider her team is currently describing another dinosaur that could possibly be larger than the super titan.

Australia, unlike China or North America, wasn’t a great home for dinosaurs

Bri Bollmann, host of the NeoJurassic podcast, told Insider that during the dinosaur era a great deal of the landmass that is now Australia was underwater, making it difficult for dinosaurs to live and have their fossils preserved there.

“There wasn’t really a lot of available landmass for dinosaurs to be living on for much of their time on earth,” Bollmann said.

A rendering of the Australotitan cooperensis dinosaur discovered in Australia.

It’s not that dinosaurs didn’t live in Australia, but simply that much of the landmass was underwater and areas that would have been prime real estate for finding fossils have “been brutally eroded down to nothing,” Bollmann said.

“They’re definitely out there, but it’s certainly more of a challenge than say North America or China, for instance, where fossils are just shooting out of the ground left and right,” Bollmann said.

That reality made people very pessimistic at the idea of finding fossils on the continent. Mackenzie said she didn’t believe there were any until American paleontologist Paul Sereno visited Australia in search of fossils in 1998.

Sereno, a professor at the University of Chicago who has discovered several new dinosaur species in countries from Morocco to Argentina, left the continent empty-handed.

“[Sereno and his team] left with the belief that it was possible. There was enough geological evidence to sort of show fossilized evidence, not dinosaurs necessarily, but plants and other kinds of small things,” Mackenzie said.

Mackenzie never imagined that her family would be on this journey

Mackenzie and her family were sheep and cattle graziers. While her husband in particular was fascinated with dinosaurs, they never imagined ever doing any work in paleontology.

“Our family was around all this when [Sereno] came and so obviously got inspired by all that,” she said. “[We] still had no idea what it was going to look like since they didn’t find any dinosaur fossils at that point. We were feeling very confident. We knew it was very possible but we just really didn’t know too much about it.”

But after her son discovered the bone on their property a few years after Sereno left Australia, they realized there could be more and began learning about dinosaurs and digging. Finding one fossil led to finding many, until eventually Mackenzie and her team found the largest in the country.

“It’s such an unexpected thing and I guess not in my wildest dreams would I have ever thought previous to the day that that first piece of bone was found that I would be doing what I’m doing today,” she said. “It’s quite extraordinary when you think back on that fist-size piece of bone that our son found in 2004, which he easily could have just left on the ground and kept going. But he picked it up and that marked a change in the history of our paleontology, a change in the history of the path our family has taken.”

By understanding how and where they lived, we could understand more about how dinosaurs may have gone extinct

Bollmann said the Australian discoveries could give greater insight into how dinosaurs lived and allow us to understand how some of the largest creatures to graze the earth went extinct, which could be a lesson for humans.

He explained that the discovery of these large dinosaurs shows how they grew and developed to adapt to their environment, but ultimately it was that very large growth that helped bring about their extinction.

For humans, he said, we’re developing at such a fast pace, with so many different ecosystems we rely on for our survival that if any were to malfunction, we may also become too big for our own survival.

“What I think is interesting about these dinosaur discoveries and what we’re learning about in Cretaceous species and
Titanosaurus is again a reminder or perhaps a warning to people to realize that we are very much linked with the natural world and we think we’re above it and we think we can navigate these crises better than we actually can,” he said.

He said learning about how and what happened to the dinosaurs through these discoveries can help people learn “where we are in our relationship with the world today. I think that is the strongest value that we can have.”

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Discovered in Australia, ‘the southern titan’ – a 16 foot tall dinosaur almost the length of a Boeing 737 – has been classified as a new species

A rendering of the Australotitan cooperensis dinosaur discovered in Australia.

  • A dinosaur found in Australia is now one of the 15 largest in the world.
  • “The southern titan” is 16 feet tall and a little under 100 feet long.
  • Scientists categorized it as a new species believed to have lived 92 to 96 million years ago.
  • See more stories on Insider’s business page.

A 16 foot tall and almost 100-foot long dinosaur was discovered in Australia, making it the largest found in the country.

It’s close to the length of the Boeing 737 aircraft, which is 110 feet long.

The skeleton was discovered in 2007 and is now a new classified species, called Australotitan cooperensis.

Australotitan or “the southern titan” is one the 15 largest dinosaur specimens found in the world and was documented in a study published Monday in the science journal PeerJ.

Australotitan adds to the growing list of uniquely Australian dinosaur species discovered in Outback Queensland, and just as importantly showcases a totally new area for dinosaur discovery in Australia,” Scott Hocknull, one of the lead scientists of the new study, said in a press release.

Dr. Scott Hocknull and Robyn Mackenzie pose with a 3D reconstruction and the humerus bone of "Cooper," a new species of dinosaur discovered in Queensland and recognized as the largest ever found in Australia.
Dr. Scott Hocknull and Robyn Mackenzie pose with a 3D reconstruction and the humerus bone of “Cooper,” a new species of dinosaur discovered in Queensland and recognized as the largest ever found in Australia.

The fossil was initially nicknamed “Cooper” since it was discovered on a farm near Cooper Creek in southwest Queensland.

The report said the species likely lived during the Cretaceous Period, somewhere between 92 to 96 million years ago, and were a type of giant sauropod, a group of herbivores that had very long necks, long tails, small heads, and four thick, pillar-like legs.

Late last year, scientists were puzzled by another dinosaur discovery: a species that had long hair and stiff ribbon-like structures coming from its shoulders.

It was named Ubijara jubatus. Scientists think it lived around 110 million years ago in northeastern Brazil.

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Tyrannosaurs may have hunted in packs like wolves, a new study says, undermining the idea they were solitary predators

A boy looks inside the skull of a Tyrannosaurus Rex replica at the Egidio Feruglio Museum in Trelew, Argentina, in this May 18, 2014 file photograph. REUTERS/Maxi Jonas/Files
A boy looking inside the skull of a Tyrannosaurus rex replica.

  • New evidence suggests that tyrannosaurs hunted as a pack animal.
  • The dinosaur remains were found in the Grand Staircase-Escalante National Monument in Utah.
  • Scientists had previously thought that the tyrannosaurs’ brains were too small for this kind of complex behavior.
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Tyrannosaurs were probably social animals who hunted in packs, according to research from the University of Arkansas published Monday.

The research challenges a common theory that the huge lizards were solitary hunters who chased down prey alone, perhaps because they were too stupid to cooperate.

The tyrannosaur category includes the famous Tyrannosaurus rex as well as similar-looking carnivores likes the Albertosaurus and Gorgosaurus.

“A lot of researchers feel like these animals simply didn’t have the brain power to engage in such complex behavior,” Alan Titus, a paleontologist for the Bureau of Land Management who led the research, told reporters in an online briefing, The Washington Post reported.

But this research suggest that the animals hunted in packs, like wolves, or like the velociraptors hunting together in “Jurassic Park.”

The scientists looked at the remains of four or five tyrannosaurs aged roughly between 2 and 44 years of age, found in Utah in the Grand Staircase-Escalante National Monument.

This was the first tyrannosaur mass death site found in the southern US, The Post reported.

The results of this investigation, published in the peer-reviewed journal Peer J on Monday, suggest that the dinosaurs died while hunting together, challenging the idea that they only hunted alone.

An artist representation of the dinosaurs, in this tweet from the Bureau of Land Management Utah, shows how they might have died:

Grand Staircase-Escalante national monument is one of two Utah monuments that President Joe Biden pledged to restore as part of his campaign.

The fossils “are national treasures,” Titus said, The Guardian reported. “They’re part of the story of how North America came to be and how ultimately we came to be.”

T. Rex foot rainbows and unicorns quarry
The front arms of a tyrannosaurus found at the Rainbows and Unicorn Quarry

T. Rex
A tyrannosaur’s skull found two miles north of the “Rainbows and Unicorns Quarry” on February 26, 2019.

“This is a cool analysis,” Professor Mike Benton, a professor of vertebrate paleontology at the University of Bristol, UK, told Insider in an email. “They have a smart method that makes sense, and the results are plausible,” he said.

“In a way, it was a question we never asked,” Benton said. Until recently, “it was fanciful even to try to estimate how many dinosaur individuals existed on Earth,” Benton said.

A separate study, also out this week, found that 2.5 billion fully grown T. rexes roamed the Earth over the 2.5 million years that the species was around, Insider’s Aylin Woodward reported.

The site where the remains were found was nicknamed Rainbows and Unicorns Quarry because of the abundance of turtle, fish, alligator, and dinosaur remains found there.

Grand Staircase-Escalante National Monument
Grand Staircase-Escalante National Monument in Utah.

Its discovery was sheer luck. Titus and a group of volunteers went to the site in 2014 to look at the turtle remains.

During a freak storm, they were stranded. But they were rewarded when the heavy rain uncovered a T. Rex bone.

The tyrannosaurs in the Rainbows and Unicorn quarry are thought to come from the Teratophoneus species, The Guardian reported.

The findings build on the discovery of other sites where bones were found huddled together, the scientists said in a statement.

One was in Canada, where 12 individuals tyrannosaurs of the Albertosaurus species were found in Dry Island Buffalo Jump park.

“This must be reflecting some sort of behavior and not just a freak event happening over and over again,” Titus told reporters.

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A whopping 2.5 billion fully grown T. rexes walked the Earth in the course of the species’ existence, paleontologists found

Jurassic Park T Rex
A T. rex depicted in the 1993 film “Jurassic Park.”

An adult Tyrannosaurus rex required a lot of space – and the prey therein – to survive.

According to new calculations from paleontologists the University of California, Berkeley, each adult T. rex lived in an area roughly 40 square miles in size.

The study, published Thursday in the journal Science, uses that math to offer an estimate of the total number of these predators that walked the Earth during the Cretaceous Period, between 66 and 68 million years ago: an impressive 2.5 billion.

“The total number did catch me off guard,” Charles Marshall, a paleontologist at Berkeley who co-authored the study, told Insider.

Marshall’s analysis suggests that the entire island of Manhattan or city of San Francisco would be the territory of a single T. rex.

He said he’d been wondering for years how unusual it really is to find a T. rex fossil: “When I hold a fossil in my hand, I always said to myself, ‘I know this is freakishly rare.’ But just how rare is it – one in a million or one in a trillion?”

Comparing the T. rex to the Komodo dragon

The T. rex was one of the largest carnivorous land animals that ever walked the Earth. (That accolade currently goes to the polar bear.) An adult Tyrannosaurus rex could weigh at least 5 tons. It stood about 12 to 13 feet tall at the hip and was about 40 to 43 feet long.

The larger predators are, the fewer of them can live in the same area, since there just isn’t enough food to sustain their massive size. This is known as Durham’s Law. So if researchers know how many calories a meat-eater needs to survive, they can calculate the number of predators per square mile.

While there’s no living predator that resembles the T. rex in size, Marshall compared the dinosaur’s energy needs to those of a Komodo dragon, the largest lizard on Earth.

Komodo Dragon
A Komodo dragon in Indonesia’s Komodo National Park.

Using that benchmark, he calculated that there could have been roughly 3,800 T. rex in an area the size of California at any given time – or just two in an area the size of Washington, DC.

There were about 20,000 adult T. rexes living at one time

Marshall’s team also needed to calculate three other variables to determine the total number of rexes that ever walked the planet: the total land area of suitable T. rex habitat, the dino’s average life span as an adult, and how long these predators existed on Earth.

T.rex illustration
A full-grown Tyrannosaurus rex weighed about 6 to 9 tons, stood about 12 to 13 feet high at the hip, and measured about 40 to 43 feet long.

By reviewing the locations of every T. rex fossil ever found, the study authors determined that the predator lived in about 888,000 square miles of North America – and nowhere else on Earth. Although the animal might have been able to survive in the area that’s now Siberia, Marshall said, he’d be surprised if any rex fossils were ever found outside the one continent.

Using that assumption about the T. rex’s geographic range, Marshall calculated that there could have been about 20,000 adult T. rexes alive at any given time in the species’ existence.

Figuring out how long the T. rex species was around was a bit easier – the oldest rex fossil ever found suggests the dinosaur walked the Earth for the last 2.5 million years of the Cretaceous Period, starting 68 million years ago. Then it went extinct after the Chicxulub space rock struck.

Finally, Marshall’s team calculated how long one generation of adult rexes lasted by looking at the average time span between when rexes became fully grown – at around age 15 – and when they died in their early 30s.

An artist’s depiction of a juvenile Tyrannosaurus rex.

That means that in the 2.5 million years these animals were on Earth, there were about 127,000 generations of them. Multiply that number by 20,000, and you wind up with 2.5 billion T. rexes.

However, Marshall pointed out that this number doesn’t include baby or juvenile T. rexes. Those were excluded from the calculations because research suggests juvenile rexes were smaller and faster than their adult counterparts, so hunted different prey.

T Rex in New York City
A Tyrannosaurus rex skeleton, named STAN, displayed by Christie’s Auction House in New York City, September 15, 2020.

Marshall’s team’s estimate suggests that the remains of just one in every 80 million adult T. rexes have been found. Currently, there are about 32 well-preserved, adult T. rex skeletons in public museums worldwide, Marshall said.

That means we’ve only dug up 0.00000125% of all the adult T. rexes that ever lived.

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The space rock that doomed the dinosaurs was shrapnel from a comet that flew too close to the sun, a Harvard study suggests

dinosaur asteroid meteor
An artist’s depiction of the moment the Chicxulub asteroid struck present-day Mexico 66 million years ago.

About 66 million years ago, a space rock more than 6 miles wide collided with Earth, striking land that is now part of Mexico.

The impact sparked wildfires that stretched for hundreds of miles, triggered a mile-high tsunami, and released billions of tons of sulfur into the atmosphere. That gaseous haze blocked the sun, cooling the Earth and dooming the dinosaurs, along with 75% of all life on the planet.

But the origins of that dinosaur-killing rock, named Chicxulub, have remained a mystery. 

Most theories suggest Chicxulub was a massive asteroid; hundreds of thousands of these rocks sit in a donut-shaped ring between Mars and Jupiter. But in a study published Monday, two Harvard astrophysicists suggested an alternate idea: that Chicxulub wasn’t an asteroid at all, but a piece of shrapnel from an icy comet that had been pushed too close to the sun by Jupiter’s gravity.

Asteroids and comets are both classified as space rocks by NASA, but they differ in key ways: Comets form from ice and dust outside our solar system and are generally small and fast-moving, whereas rocky asteroids are larger, slower, and form closer to the sun.

“We are suggesting that, in fact, if you break up an object as it comes close to the sun, it could give rise to the appropriate event rate and also the kind of impact that killed the dinosaurs,” Avi Loeb, an astrophysicist and cosmologist at Harvard University and co-author of the new study, said in a press release

The solar system acts like a ‘pinball machine’ for comets

asteroid meteor armageddon shutterstock
An artist’s depiction of an asteroid approaching Earth.

Most asteroids come from the asteroid belt between the solar system’s inner and outer planets. But NASA scientists who keep tabs on space objects that pass near Earth have yet to figure out where Chicxulub came from. 

In the new study, published in the journal Scientific Reports, Loeb and his co-author, Amir Siraj, suggest Chicxulub didn’t come from the asteroid belt. Rather, they say it more likely originated outside our solar system, in an area called the Oort cloud

Think of the Oort cloud as ring made of 1 trillion pieces of icy debris, which sits beyond the farthest reaches of the solar system, surrounding it. It’s located at least 2,000 times farther away from the sun than Earth is. Comets that originate in the Oort cloud are known as long-period comets because they take so long to complete one orbit around the sun.

But these comets can sometimes get pulled off-course by the gravity of massive planets like Jupiter. Such a tweak to a comet’s orbit could send it hurtling on a path much closer to the sun. 

“The solar system acts as a kind of pinball machine,” Siraj said in the release.

Comets that get near the sun are called “sungrazers.” The new study calculated that about 20% of Oort cloud comets are sungrazers. As they approach our star, its gravity starts to pull them apart. Fragments of comet slough off and may careen toward nearby planets. 

This, the study authors say, is “a satisfactory explanation for the origin of the impactor” that killed the dinosaurs.

The asteroid-versus-comet argument isn’t settled

Chicxulub_impact asteroid
A painting depicting an asteroid slamming into tropical, shallow seas of the Yucatan Peninsula in what is today southeast Mexico. The aftermath is believed to have caused the extinction of the dinosaurs.

Siraj and Loeb aren’t the only scientists who think a comet, not an asteroid, doomed the dinosaurs. A group of researchers from Dartmouth College similarly suggested in 2013 that a high-speed comet could have created the Chicxulub crater. 

Chicxulub hit Earth at a speed of 12 miles per second (43,200 mph), which is about 30 times faster than the speed of a supersonic jet. The resulting 100-mile-wide crater extended 12 miles into the depths of the Gulf of Mexico. Some scientists have estimated the asteroid’s power was equivalent to 10 billion of the atomic bombs used in World War II.

But not all researchers are convinced a comet caused that destruction.

Natalia Artemieva, a senior scientist at the Planetary Science Institute in Arizona, told The New York Times that comet fragments from a sungrazer would have been too small to create the Chicxulub crater. And Bill Bottke, a planetary scientist at the Southwest Research Institute in Colorado, suggested that the study overestimates the frequency of sungrazers – and, consequently, the amount of fragments those comets produce.

Existing evidence favors the idea that Chicxulub was an asteroid, “but it’s not conclusive,” Bottke told the Times. “There’s still wiggle room if somebody really wants it to be a comet. I just think making that case is really hard.”

Siraj and Loeb, however, said their theory is supported by a type of material found deep inside the Chicxulub crater and other craters in South Africa and Kazakhstan. That substance, carbonaceous chondrite, may have come from comets. Whereas just 10% of asteroids from the asteroid belt are composed of carbonaceous chondrites, the material “could potentially be widespread in comets,” the study authors wrote.

The only samples ever collected from a comet in space were brought back in 2006. They revealed that object, called Wild 2, was composed of carbonaceous chondrite.

kuiper belt oort cloud
Artwork depicting the icy cores of baby comets beyond Neptune at the edge of our solar system.

Finding the correct answer in the Chicxulub debate is useful because it could help researchers figure out the likelihood of a similar impact event in the future. Only two to three comets from the Oort Cloud have hit Earth during the last 500 million years, according to one study. By contrast, according to the Planetary Society, a Chicxulub-sized asteroid impacts Earth every 100 million years or so

Siraj and Loeb modeled how many long-period comets get close enough to the sun to shed large fragments in the direction of Earth. Their numbers suggest 10 times more Chicxulub-sized objects hit Earth over its history than scientists previously thought.

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