Second Gunman in Death of the Dinosaurs

A cunning study of geology, shells and ancient magnetism offers clues to a long-ago extinction

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If you’ve already heard that dinosaurs are extinct — and the betting is that you have — you’ve probably also heard the reason: an asteroid smashed into Mexico’s Yucatán Peninsula some 65 million years ago, blasting enough dust into the atmosphere to block the sunlight and dim the skies. These days that’s Intro to Dinos stuff, but prior to 1980, the thinking was very different. Dinosaurs endured a long, slow decline, the theory went, ceding their rule of the planet only gradually and grudgingly. The old theory is nearly as extinct as the beasts themselves — or at least it was until last week, when a new study pumped a little life back into it. About 200,000 years before the asteroid hit, a separate extinction was already under way, wiping out numerous species of clams and snails on the ocean floor. And it was terrestrial volcanoes, not a rock from space, that were to blame.

The new findings, published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, are the product of three years of summer visits by researchers to Seymour Island, on the Antarctic Peninsula. Polar regions make research hard — one year the ice was so thick that the scientists’ boat couldn’t reach the shore — but when the weather cooperates, the sites offer fossil hunters distinct advantages. One is that, like today, the ancient poles were more susceptible to climate change. Ice then was the same as ice now, which is highly reflective. As it melts, it gives way to darker ocean water, which absorbs more light and heat, exacerbating warming in an accelerating loop. In this case, scientists wanted to determine temperatures in the polar ocean from 65 million years ago, so they gathered more than 100 ancient, 2-in.-wide (5 cm) shells from subterranean samples, then analyzed the minerals and calcium carbonate that had formed the shells.

(MORE: Just Big-Boned? Dinosaurs Skinnier than Once Thought)

Those ancient artifacts revealed a lot. Calcium carbonate — an organic stew of calcium, carbon and oxygen — is nature’s answer to a stuck thermostat, with the environmental conditions when the material formed forever stamped into its chemical makeup. The oxygen portion has two variants: oxygen-16 and oxygen-18. If there’s more oxygen-16, seawater temperatures were higher when the shell formed — and that’s exactly what the scientists discovered, in this case an estimated 9ºF (5ºC) temperature jump from typical seawater temperatures. By matching that information with the strata layers where those oxygen-16-rich shells were found, geologists identified three periods of ocean warming: about 2 million years before the great dinosaur extinction, then 250,000 years before and again about 200,000 years after.

All three of those eras coincide nicely with volcanic events in India’s Deccan Plateau, which may have belched enough carbon dioxide and other greenhouse gases to boost planetary temperatures and harm ocean dwellers. “If this warming is severe enough to be impacting marine life, it’s likely impacting terrestrial life too,” says Tom Tobin, a doctoral student at the University of Washington and the report’s lead author. “So it’s not unreasonable to think that the environmental stress from the volcanism contributed to the strength of the asteroid extinction. One of [the events] is synchronous with the marine extinction that we found 200,000 years before the asteroid impact.”

(MORE: The Robotic Dinosaurs That Could Change Paleontology Forever)

Such relatively specific dates underscore another reason the scientists chose their Antarctic research site: it offers unusually thick, 3,200-ft.-deep (1,000 m) sediment, and the deeper the sediment is, the more layers of geologic time have been preserved. This region apparently built up more than most because of repeated sediment deposits during uplift of the mountain range that makes up the Antarctic Peninsula. In fact, the Seymour Island site has so many sediment layers that scientists could whittle the time intervals down to hundred-thousand-year scales — a minuscule window compared with the 10-million-year degree of accuracy most sites provide.

Even this geologic precision, however, wasn’t enough to seal the deal, at least not to an acceptable scientific certainty. So the scientists used an imaginative method, matching changes in Earth’s magnetic field to different layers in the strata. Though most people assume magnetic north is a constant, it isn’t. Every 500,000 years or so — and in random periods ranging from as little as 100,000 years to 30 million years — the magnetic north pole flips to the south pole. When it does, magnetic particles in slow-building sediments orient themselves accordingly, then become locked in place as further sediment builds.

(MORE: Rewriting the Book on Dinosaurs)

With this in mind, the researchers drilled core samples and compared the particles’ orientation with the known history of magnetic-field changes. That provided confirmation that the earlier oceanic extinctions occurred within the range of Deccan volcanism. “Once we compared the warming record to the timing of the volcanism,” says Tobin, “we realized, Hey, these things seem to line up pretty well. This is pretty cool. It brings more complexity and nuance to the picture we already had.”

Intrigued by the possibility of further reconciling extinction theories, the researchers are searching for a second site with the rare, deep sediment layers necessary for a close-up look at the late-Cretaceous period. For the moment, it seems that both volcanoes and the infamous asteroid may have contributed to the dinosaurs’ demise — a tidy addendum to Dino 101.

VIDEO: Resurrecting Dinosaurs: From Fossil to Museum Floor

89 comments
Jill Louis
Jill Louis

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53underscore3
53underscore3

It's a pretty believable scenario, but being able to define a separation of 200,000 years is a very, very difficult undertaking.  I'm not sure that radiometric dating has error bars significantly less than that, which certainly means the Chixulub impactor's timing can't be constrained more tightly.

There are two problems I see:

1. The 5C increase is not particularly significant as an impact on life, secular warming (still caused by the Deccan Taps) features much greater polar temps, and may have even enhanced life for dinosaurs in polar regions - without significantly impacting equatorial zones.  Any dieoffs recorded locally in the sea may be attributed to changes in polar temperatures only, and not even across the planet, let alone all the oceans.  We see this in Quaternary sediments with a vengeance.

2. Though geological superposition rules apply to the strata that were studied, it is extremely difficult to prove that, given the error bars in dating the iridium / impact layer, that sedimentary deposition took place at the same rate throughout the geological column.

Like I said, believable, but there are too many ifs.  They have to prove that life on both land and sea worldwide was affected from the equator to the poles for this one to stick!

dino6622
dino6622

My favorite quote...from "The Life of PI",..."Agnostics.... are under the thrall of reason, that fool's gold for the bright....Atheists are my brothers and sisters of a different faith....Like me they go as far as the legs of reason will carry them----and then they leap."

tma_sierrahills
tma_sierrahills

I guess this is the dinosaur second gunman on the grassy knoll theory. Seriously, good article, although if anyone has watched some of the finer scientific documentaries dealing with all of this over the last few years, it is often clearly stated that before the asteroid impact, the dinosaurs were already under extreme stress and being thinned out by rapid climate changes, which partly involved lots of volcanic eruptions and greatly reduced food supplies. Of course birds are now said to be the only survivors of the dinosaur line. 

Somehow it makes the dinosaur story even sadder that their remaining toughest surviving members, after having soldiered through countless natural disasters, from reversing magnetic poles, to mega-volcanoes, find themselves looking up into the sky only to see a humongous space rock heading straight for them. "What are the chances?" you can almost imagine them remarking. We've all had days like that. 

Of course we are currently living through another historic period of massive extinctions, this one caused by humans, mostly through habitat destruction. So we can think of ourselves as being the modern day equivalent of a brainless unbelievably destructive big fat asteroid.

gracetoday
gracetoday

Readers should keep in mind the power of the paradigm to profoundly affect the interpretation of past data. All of this data mentioned fits very well within a recent flood scenario, even better actually. It's very strange that the past is so littered with these random massive extinctions that completely decimate the most unexpected species, while leaving other, more vulnerable ones, intact and unchanged up to today. If we see the fossil record as the record of successive destruction of a flood however, the data begins to make much more sense. All this scientifique study proves is that the burial of this sea life was happening at the same time as those volcanos were errupting. But it could have very well happened within a very short time, during a global tectonic catastrophe that recycled the ocean floor and flooded all the continents, as UCLA and Los Alamos national laboratories geophysicist John Baumgardner proposed and modelled in Tera, a real-time tectonic simulation program.  I also found amusing the suggestion that dating layers using the magnetic orientation of volcanic rocks in those layers somehow novel or groundbreaking. This method has been around for almost 40 years.

BubbaCo
BubbaCo

 GOD DAMN that must've been a big ole asteroid. Poor dinosaurs...if they were still alive, they'd be republicans.

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Papa Foote
Papa Foote

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Phadras Johns
Phadras Johns

Arg. This here paleontology is a mighty shifting sort. One days she's a blaming an asteroid, the next she's a blaming the volcanoes too. For goodness sake's do we have to blame the poor misunderstood asteroid just doing it's job floating 'round the solar system.? Aye, but oooooohhhh that's not enough now we must also attack a hard working volcano. Just puttin'in his geologic nine to five and lo 65 million years later he's a gettin'  the blame for killin' the precious dinos. For the love of Pete can't a mere celestial phenomenon and a domestic geologic disturbance get a break around here. 

Edward
Edward

I guarantee there are dinosaur fossils in Antarctica too.  Granted we're talking about an enormous amount of time it's still fascinating. 

Ed M.
Ed M.

So when will the next volcanic maximum occur?

f_galton
f_galton

Not all dinosaurs went extinct, some of them made it to the entrance at the North Pole and retreated into the hollow earth where they still live today.

Tom
Tom

How did I know this would eventually get to climate change killed the dinosaurs?

GetaQlue
GetaQlue

So, after the big rock hit our planet and the poles reversed and all the Dino's died (except those that were smart enough to evolve wings and learend to fly?), where did Homosapians come from? Did we just grow out of the organisms left in the muck? Or did the much grow apes that evolved into Homosapians? (spelling??). Oh wait, there were 3 disctinct versions of man.......... interesting...... SO only some of the apes evolved and the rest decided to stay apes? What has evolved lately, or did evolution just stop now that we exits???????????? Ok.... you are right! The Earth and all that lives on it are the result of some great cosmic accident. SOme rocks crashed into each other and Coalesced created a perfect environment for life........ awesome........... For all atheists, who has more to lose by being wrong?

williepitt
williepitt

Calcium carbonate is "an organic stew of calcium, carbon and oxygen"? Nonsense and bushwah.

Calcium carbonate is calcium carbonate, a single inorganic compound. Anyone who says otherwise is an ignoramus.

williepitt
williepitt

Calcium carbonate is "an organic stew of calcium, carbon and oxygen"? Nope. What a stupid thing to say!

Calcium carbonate is just that: calcium carbonate. A single inorganic compound. Anything else that is said is bunk.

Jon
Jon

BLASPHEMY!   How could the dinosaurs die out 65 million years ago if the Earth was only created only a few thousand years ago?  Everyone knows that people were riding dinosaurs (ala the Flintstones) and they all died out as a result of Noah's flood.

NYVeteran
NYVeteran

I consulted Faux News and as I expected extinction was actually Obama's fault.  Murdoch was actually there at the extinction and just like his news, their version is much more entertaining than the facts.

Mark Lukas
Mark Lukas

The Dinosaurs were shot? From behind the grassy knoll? WHAT?!

misterdanton
misterdanton

not only was a nurse discussing the trust issues of looking at hemoglobin under a microscope, but the dinosaur specialsists that confirm that the Reptilian stegosaurus has a brain the size of a walnut is convincing too.

iolaisinwisconsin
iolaisinwisconsin

The 'second gunman' lava event in India has been well known for years. The Chicxulub impact event was the coup de grace for the dinosaurs, but they had been dying off for a while before that.

I would assume the work tightening the timeframe was the point of this article, but it really didn't cover any new ground.

cwarner7_11
cwarner7_11

Not all dinosaurs went extinct.  The smart ones just got a whole lot smaller and learned to fly.  The world is full of their descendants today...

David128453
David128453

What are these dinosaurs you talk about?  God created man and there is no mention of dinosaurs or their extinction.  They must be a myth.

MicheleIsHot
MicheleIsHot

All of this talk about 65,000,000 years ago and 200,000 years ago is just that stupid science.  If it ain't in the bible. it ain't true.  Isn't that right, Mrs. Palin?  You betcha!

dot2dotnews
dot2dotnews

If only we had every human mind at our disposition I think that we would be able to do something. If the Chinese or Russian or Syrian or Iranian government didn't spend soo much time trying to contain free thought we may make it. If we were all democratic we wouldn't need to erect weapons in defence of one another. I also believe that there should be a massive budget allocated for science and the prevention of an extinction event by a coalition of nations, thus incentivising more to follow. 

18235
18235

"an asteroid smashed into Mexico’s Yucatán Peninsula some 65 million ago"

mexico once again to blame.