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An illustration of dinosaurs fleeing a meteorite impact.

An illustration of dinosaurs fleeing a meteorite impact.

Illustration by Mark Garlick, Science Source

Ker Than

for National Geographic News

Published February 12, 2013

New insights about the asteroid thought to have killed off the dinosaurs suggest it may have just been the final blow, and that the reptiles were already suffering from a finicky climate prompted by volcanic eruptions long before the meteorite struck.

"The [asteroid] impact was the coup de grace," Paul Renne, a geologist at the University of California, Berkeley, said in a statement.

The research, detailed in the February 8 issue of the journal Science, adds to the ongoing scientific debate over what exactly killed off the dinosaurs.

That debate, which once revolved around the question of whether the culprit was an asteroid or volcano-induced climate changes, has evolved to consider the possibility that perhaps multiple environmental factors were involved.

Renne and his team recently determined the most precise date yet for the asteroid strike, which occurred in the Yucatán Peninsula in what is now Mexico.

Using a high-precision dating technique on tektites—pebble-sized rocks formed during meteorite impacts—from Haiti that were created during the event, the team concluded that the impact occurred 66,038,000 years ago—slightly later than previously thought.

When error limits are taken into account, the new date is the same as the date of the extinction, the team says, making the events simultaneous.

Renne said the new findings should lay to rest any remaining doubts about whether an asteroid was a factor in the dinosaurs' demise.

"We have shown that these events are synchronous to within a gnat's eyebrow," he said, "and therefore the impact clearly played a major role in extinctions."

That is not to say, however, that the asteroid—which carved out the so-called Chicxulub crater—was the sole cause of the dinosaurs' extinction.

Evidence now suggests massive volcanic eruptions in India that predated the asteroid strike also played a part, triggering climate changes that were already killing off some dinosaur groups.

For example, "nobody has ever found a non-avian dinosaur fossil exactly at the impact layer," Renne said in an email. "Hence, strictly speaking, the non-avian dinosaurs"—those dinosaurs unrelated to birds—"may have already gone extinct by the time of the impact."

Death From the Skies

The idea that volcanism was responsible for the dinosaurs' demise actually predates the impact theory, and it fits well with what is known about Earth's other mass extinction events.

"Many of the other mass extinctions have been found to co-occur with large-scale volcanic eruptions," said Heiko Pälike, a paleoceanographer at the University of Bremen in Germany.

But in the 1980s, father-son team Luis and Walter Alvarez, a physicist and planetary scientist, respectively, presented a bold new theory.

After discovering that a layer of clay that's found throughout the world and that coincided with the end of the Cretaceous period is enriched in iridium—an element rare on Earth but common in space rocks—they proposed that a meteorite wiped out the dinosaurs.

"As the impact theory took hold, especially with the more physical scientists ... the volcanists lost ground," Renne explained.

The impact theory gained further momentum in the 1990s, when scientists discovered a 110-mile (180-kilometer) wide impact crater in the Yucatán Peninsula that dated to the boundary between the Cretaceous and Tertiary periods—the so-called KT boundary—when the dinosaurs disappeared.

The crater's size indicated that whatever created it was roughly 6 miles (10 kilometers) in diameter.

An asteroid of that size striking the Earth would have had devastating consequences, including destructive pressure waves, global wildfires, tsunamis, and a "rain" of molten rock reentering the atmosphere.

Additionally, "much additional particulate matter would have stayed afloat in the atmosphere for weeks, months, perhaps years, blocking incoming solar radiation and thus killing plant life and causing catastrophic drops in temperatures," explained Hans-Dieter Sues, a paleontologist at the Smithsonian National Museum of Natural History in Washington, D.C.

Hybrid Theory for Dinosaur Extinction

The once-abandoned volcanism theory has seen a revival of sorts in recent years, however, as a result of fresh insights about a period of sustained ancient volcanic activity in India and the discovery that dinosaur diversity may have already been declining before the asteroid strike.

The debate now is "whether the Chicxulub impact was the 'smoking gun,' as many researchers claim," Sues said, "or one of several causative factors, kind of like 'Murder on the Orient Express.'"

Renne belongs to the camp that thinks a series of volcanic eruptions in India that produced ancient lava flows known as the Deccan Traps caused dramatic climate variations, including long cold snaps, that may have already been culling the dinosaurs before the asteroid struck.

"It seems clear that volcanism alone, if on a sufficiently massive and rapid scale, can trigger extinctions," Renne said. "Thus my view that the impact was probably the final straw, but not the sole cause."

Unanswered Questions

The new hybrid theory still has some major questions it must answer, however, like precisely how much the Indian volcanic eruptions affected the dinosaurs.

"Some people say if you look at the eruption of Mount Pinatubo [in 1991], it cooled the Earth for a short period of time due to the aerosol and the dust that was ejected," Pälike said.

But "others say in the long run volcanoes probably pump more carbon dioxide into the atmosphere and actually warm the planet, at least temporarily."

It's also unclear how the Deccan Traps eruptions were spread out in time. "We know that they started a few million years before the end of the Cretaceous and lasted for several million years after, extending even beyond the [asteroid impact]," Pälike said.

"However, some people have suggested that there were clusters of eruptions that happened within a span of a few tens of thousands of years."

Knowing the timing of the eruptions is important, Pälike added, because if they were happening close to the end of the Cretaceous, it's more likely they played a role in the dinosaurs' extinction than if most of the eruptions happened two million years before.

Pälike thinks that more precise dating of the volcanic ash layers in India could help answer some of the remaining questions: "That's the next step of the puzzle."

Pinning down the cause of the dinosaurs' extinction isn't just of academic interest, said Jonathan Bloch, associate curator of vertebrate paleontology at the Florida Museum of Natural History at the University of Florida.

"It's important for us to understand how ecosystems respond to big perturbations," Bloch said, "whether it's gradual climate change or a catastrophic event. These are all things we have to think about as humans on the planet today."

16 comments
Kara Keenan
Kara Keenan

I CANNOT believe someone is actually talking about the bible here. Leaving now. *Face Palm*

Angela Post
Angela Post

Great topic for a science lit review!

Chase Boyd
Chase Boyd

I am fairly sure that it would be impossible for someone to tell of such an event after it happened. For example, why would you think humans would survive such a blast when 20 ton dinosaurs were disintegrated. Even if we did have humans that lived past it what are the chances that they would be able to identify what happened and also start one of the worlds most renowned books afterwords?

RO RI
RO RI

There is an obvious time gap right after Genesis 1:1 when space and time were created perfect: 

Gen 1:1  "In the beginning Elohim created the heavens and the earth." 

This time gap could have taken billions of years in total and then the next thing that is described is presented matter of fact as chaotic but the root cause is left unexplained:

Gen 1:2a But the earth came to be ruined and despoiled. And darkness was on the face of the deep

Genesis doesn't explain how the earth became ruined and despoiled after the time gap and doesn't explain the darkness but it was possibly the product of the volcanic ashes and the firestorm than rained down after the asteroid hit in Yucatan 66 million years ago....the darkness also extinguished the dinosaurs....the six day re creation is further down presented but it is distinct from the original creation in Genesis 1:1

Jared Mimms
Jared Mimms

Exactly, the extinction of the Dinos was not solely the result of a meteor impact. As matter in three dimensions moves due to gravity and other forces, the angular velocity and magnitude of gravitational forces exerted on every molecule on Earth changes. A sudden shift in the magnitude or direction of gravitational forces from bodies of matter and mass very far away (think black holes colliding in space as a simplistic example) could break a molecular mechanisms important in life. The operating system is changing, breaking C functions (DNA). A particular C function/object no longer work to produce the same result (functional protein, protein does not function in same way, localized differently in cell). Thus, shifts in gravity not only result in the breakage of molecular mechanisms, but aging as well. Mass extinction is the end result of omega aging - organisms cannot evolve fast enough to respond to the changing operating system. Thus, these shifts are a driver of evolution as well (selective pressure).

Victor Gaw
Victor Gaw

The rational approach by scientest is similar to a homicide detective looking for the what killed off the dinosaurs and others extinctions.  Volcanism and Asteroid impact could be the proverbial smoking gun. But there could also be other causes, there may have an unknown adverse climatic invironmental factor, bacterial, microbial or viral pathogens that finish them off. 

Contrary to rational scientific investigations, Religions (Christianity) already have the answers and it's written in black and white in their holy book. God created the Universe in 6 days and rested in the seventh day. All animals appeared on earth in it's present and final form. But when they are confronted with fossils, they simply says the were buried by Satan to mislead the faithful. When given a telescope to look at the sky, the learned princes of the church refuse to even look in the instrument. Such instrument is witchcraft. It's heresy punishable by burning at the stake. Diseases are cause by evil spirits, a punishment by god for the your sins. Exorcism may be performed to rid you of the evil possessions.  In fact the new testaments have described Jesus went about casting out evil spirits onto swines, that jump off a cliff.     How can people believe and accept such nonsense?

Johnny O
Johnny O

I read that paper. The research was very well done. However, Renne's data pertains only to the dating of the iridium and bolide layers, and refining the calculation of the date of the K-T boundary. Renne said nothing about finding dinosaur bones in the layers below right up to the newly-defined datum and then zilch above. To date, no one has found that. So who knows how many dinosaurs were still around - or what the environment was like - by the time of the impact. On the other hand, some new research out of the Antarctic region has looked at marine sediments (always more extensive than terrestrial rocks) and they show a significant extinction event at 300,000 years, in synch with the Deccan eruptions. Then these same sediments show another extinction event based on (fewer) fossils at the presumed K-T boundary. Did the earlier extinction reduce the dinosaurs to pitiful numbers for the asteroid to finally terminate? Or did the eruptions create severe enough climate change the first time around to wipe them out completely? We still do not know.

jim adams
jim adams

Robert Baaker, in his 1986 radical classic, Dinosaur Heresies says much the same -- that dinosaur populations had been diminishing for a while and the asteroid slam dunk was the coupe de gras.  He also suggests that a land bridge might have opened between continents -- as a possibility, not a probability.

Anyhow, thanks for the added info

Jared Mimms
Jared Mimms

In these extinction events, species with shorter life spans and reproductive cycles which are diverse genetically have a better chance for survival. Some organisms are just lucky and possess molecular mechanisms immune to the shift or only slightly affected by the shift - in this case, mammalian ancestors. Mammalian ancestors were also less sensitive to temperature changes because they produce their own body heat. I could also go into other dimensional tracks of reasoning as to why mammals survived, but the concept of fate is involved (would not be accepted by modern scientists). Think about what would happen if some of our vital molecular mechanisms failed as a result of said shifts, what organisms would survive? Can we predict the effects of these shifts on our own bodies by examining the changing movement (direction) and magnitude of gravitational forces in and outside our galaxy?

RO RI
RO RI

@Victor Gaw You seem to be unaware of the Genesis gap between  when space and time was created perfect. "Gen 1:1  In the beginning God created the heavens and the earth."  Time elapsed here in this Genesis gap that could be in the billions of years. If you keep reading it says that:   Genesis 1:2 But the earth came to be ruined and despoiled .   and darkness was upon the face of the deep. 

Why do you think that the earth came to be ruined and despoiled and that darkness was upon the face of the deep?   You just read that volcanic ashes in the atmosphere and from the firestorm that rained down after the asteroid  hit the earth caused darkness!   What moe evidence do you want?


Richard Bethell
Richard Bethell

@Victor GawThe last paragraph is an irrelevant distraction, unrelated to the article which never mentions religion.

As to a pathogen killing off the non-Avian dinosaurs, that seems unlikely to be any more than a minor contributing cause. Any virus able to take out saurischians and ornothischians both would also have taken out all birds. 

And yet paleognathus and neognathus birds cross the boundary (enantiornithines do not.) Given the close affinity of theropods and birds, that can't be explained by a pathogen.

Kobi P.
Kobi P.

@Victor Gaw I agree that most Religious teachings are erroneous fairy tails  however in most cases its in stark opposition to what the Bible teaches. 

For example, the matter of creation, the Bible states that the Universe and Earth existed before the Creative Days, the 6 days of creation are not 24hour periods. The 7th day has not ended and will not end until events in the Bible have come to completion. In the original texts the Hebrew word "Yom," was used, while it is translated "day" it actually has a much more extensive meaning then 24 litteral hours. I suggest you research it and see for yourself.

I say this simply because the Bible is more reasonable then most believe, and with research you might just see its not a dream for miss guided fools, it is actually quite rational.

Jared Mimms
Jared Mimms

Theoretically, if we could predict the movement, amount, and future location of all matter in the Universe, we could predict all of future reality, we could predict the future of sentience, of evolution, of everything to some degree. 

Chaka Cox
Chaka Cox

@Kobi P. @Victor Gaw lord you gave a balance reply to this!! when one actually looks into some of the 66 books in the bible it is more scientific than most think, for example the book of job has tons of facts in it....too bad the close minded teachings of the dark ages screwed up the real light of the bible...the old earth was ideal for dinosaurs bird like and the others but after the firmament was broken that covered the earth by natural events the great animals days were numbered.

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