Were dinosaurs killed off by asteroid or volcanoes? It's complicated

Dinosaur skeletons on display at Tokyo's Science Museum
Dinosaur skeletons on display at Tokyo's Science Museum

Every school child knows the dinosaurs were killed off by an asteroid smashing into the Earth some 66 million years ago.

But scientists say the story may not be quite that simple, and that over hundreds of thousands of years may have contributed to the dinosaurs' demise at the end of the Cretaceous period.

Two studies published Thursday in the journal Science contributed to a longstanding scientific debate about what exactly finished off the mighty reptiles.

Before the 1980s, the dominant theory had been that huge and prolonged caused a rapid and deadly shift in the planet's climate by sending vast clouds of ash, gas and dust into the atmosphere.

Then scientists discovered the huge Chicxulub crater of an ancient asteroid impact off the Caribbean coast of Mexico, which they posited had sent so much debris into the atmosphere that it hampered photosynthesis in plants and killed off three-quarters of life on Earth.

Ever since, scientists have maintained a lively debate about the relative contribution of each cataclysmic event to the mass die-off.

The authors of the two reports published Thursday were able to date massive lava flows with far greater precision, whittling it down from around a million years to a period of tens of thousands of years.

"We are able to recreate with great precision the order of events at the end of the Cretaceous period," Loyc Vanderkluysen, a professor of geoscience at Drexel University in Philadelphia, told AFP.

He was part of a team that dated the vast lava flows known as the Deccan Traps in India using radiation measurements. The other team used a different dating method.

The expulsion of lava there over a million years left the Deccan flows more 1,200 meters (4,000 feet) thick in places today, a volume large enough to cover an area the size of France to a depth of several hundred meters, he said.

Dinosaur wipe-out
Graphic on the catastrophic events that wiped out large dinosaurs and many other species on the planet some 66 million years ago.
No coincidence

The new dating made by the two teams match up: one found that a "pulse" of volcanic eruptions occurred just before the mass extinction.

The other is less precise but suggests that the majority of lava flows came after the asteroid hit Earth, backing up the idea that the impact triggered an earthquake so massive it would have registered 11 on the moment magnitude scale, something never witnessed by humans.

That in turn set off a wave of volcanic eruptions that lasted some 300,000 years.

"That bolsters the theory that the impact was the main cause," said Vanderkluysen. "It's like shaking a bottle of Orangina, it can accelerate ."

The close correlation of the two events—eruptions and extinction—is unlikely to be a coincidence, the researchers say.

Other periods of intense volcanic activity have coincided with mass extinction events said Blair Schoene, a professor of geosciences at Princeton and a co-author of the other study.

"The big question is, would the extinction have happened without the impact, given the volcanism, or conversely, would the extinction have happened without the volcanism, given the impact? I don't think we know that answer," he told AFP.

"The main take-home point is that it's not that simple. Nature is complicated," he added. "By studying both phenomenons in as much detail as possible, we can try and figure out what the whole story is."

Mapping the timeline of that long-ago is crucial, Schoene said, to understanding the consequences of the current so-called "sixth ,' which humans are currently causing.


Explore further

Do volcanoes or an asteroid deserve blame for dinosaur extinction?

More information: C.J. Sprain el al., "The eruptive tempo of Deccan volcanism in relation to the Cretaceous-Paleogene boundary," Science (2019). science.sciencemag.org/cgi/doi … 1126/science.aav1446

B. Schoene el al., "U-Pb constraints on pulsed eruption of the Deccan Traps across the end-Cretaceous mass extinction," Science (2019). science.sciencemag.org/cgi/doi … 1126/science.aau2422

Journal information: Science

© 2019 AFP

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Feb 23, 2019
The Volcanic eruptions that just happen to have been antipodal to the asteroid impact seem to suggest that the shockwave traveled through the earth and shattered the ground as the waves rejoined, allowing the volcanoes to flow for millions of years.

Modeling such impacts shouldn't be too hard to prove or disprove my theory.

Feb 23, 2019
At the time of the impact, India was nowhere near the antipode of Chicxulub. In fact, India was an island off the coast of Africa and passing over a hot plume, that resulted in the Deccan traps, which started long before and continued long after, the impact.

Feb 23, 2019
Can someone explain something to me. If millions of dinosaurs went extinct in a matter of days by an asteroid strike then why don't we find fossil bones of dinosaurs in the actual Kt boundary.
No bones are found above the boundary, or in the boundary. Bones are only found below the Kt boundary. In a catastrophe that large it would seem logical that the Kt boundary should be chuck full of fossil dino bones. The fact that they aren't found in the Kt boundary tells me that the dinosaurs were already extinct at the time of the impact.

Feb 24, 2019
There's a related thread running at...
https://phys.org/...red.html

Be warned: You'll need a hard-hat and Kevlar vest for the cross-fire...

@J: Did the impact 'frack' the Deccan ? They were not 'exactly' antipodal, and the different mineralogy to Mars, Moon and Mercury which *do* display 'antipodal' effects complicates modelling. Also, IIRC, there are 'differences' between Trap layers before and after. Either the plume had finally 'cleared its throat', or it was helped by a 'kick up the backside'. Or more subtle / complex ??

@AB: It takes fortunate circumstance to form and preserve land fossils. An ocean mega-impact, with blast wave, fire-fall, mega-tsunami, acid rain etc etc is about as unfriendly as you can get.
But, please, keep looking. Some-one, some-where may get lucky...

Feb 24, 2019
I'd say "a matter of days" is hyperbole. It would take years for an asteroid winter to kill off all the vegetation needed to kill off the herbivorous dinosaurs.

Feb 24, 2019
For many people, too many people, evidence is irrelevant to their belief systems.

For those who will never accept verified facts, together with those who will never agree to accept correction?
The "Truth" is a fragile bubble.

For which they have no respect & are determined to pop!

Feb 24, 2019
Here's my 2 cents hypothesis.
The Deccan volcanism released vast amounts of toxic particulate matter and gases into the atmosphere, which weakened life (especially plant) but did not wipe them out. Then came the asteroid which not only sent particulates into the atmosphere, but also an enormous amount of moisture. This moisture, then condensed, mixed with the Deccan emissions and rained down, across the planet, bringing the final extinction punch.

Feb 24, 2019
Okay, okay, stop pushing me! I'll dp it, I'll do it.

In my opinion, Antigoracle's comment seems a reasonably accurate assessment of the postulated reasons for the series of events that resulted in the End of the Jurassic Extinction Event.

It was coherent & succinct
One minor correction I would suggest:
Where you wrote "... which weakened life (especially plant) but did not wipe them out. ..."
perhaps change to:
"... climate-drien toxic fumes which weakened the large-lunged species but did not wipe them out. ..."

Your hypothesis explains why ocean-going reptiles & dinosaurs also went extinct. As they were air-breathers as are large Cetaceans today.

& that Avians could avoid & fly away from fumes.

In addition, among the land-going dinosaurs, many clades had already gone extinct. The remaining dinosaur variations were mostly herd animals & the pack predators that culled them.

As packs of Grizzly Bears hunted the great herds pf American Bison.

Feb 24, 2019
" In my opinion, Antigoracle's comment seems a reasonably accurate assessment ... was coherent & succinct."

Agreed. A couple more such, and I'll remove @ATG from my 'blocked' list...

Feb 25, 2019
I note that the main fringe that contests the well tested layer-correlated Alvarez hypothesis is represented in at least one of those papers (the principal Gerta Keller herself; https://en.wikipe...a_Keller ), and it is the one that observes pulses. It will be interesting to see if and how geoscientists welcome these papers.

And on the main I would think that observing the trap outflows before and after would detract from it rivaling the impact in causation.

- tbctd -

Feb 25, 2019
- ctd -

Meanwhile another of the large mass extinctions/climate episodes have been tied to an igneous province. The Snowball Earth Gaskier glaciation that may have paved the way for the Ediacaran fauna could have been caused by a superplume that rifted the Rodinian supercontinent into parts that would become Mexico, North America and northern Europe [ https://www.scien...2240.htm , https://agupubs.o...GL079976 ].

Seems to me the igneous provinces could have been similarly sized at ~ 10^6 km^2 (but of course the rifting of the continent changed the circulation patterns too).

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