Were the Dinosaurs Really Wiped Out by an Asteroid? Possibly Not (Update)
Written by Ian O'Neill
In 1979, the huge Chicxulub crater, measuring about 180 km (112 miles) in diameter, was discovered on the northern Yucatan Peninsula, Mexico. Scientists made the obvious conclusion that something rather large had hit the Earth in this location, probably causing all kinds of global devastation 65 million years ago. At around the same time, 65% of all life on the face of the planet was snuffed out of existence. The dinosaurs that roamed the planet up to that point were no more.
The timing of asteroid impact and the time of the mass extinction was too much of a coincidence to be ignored. When particles from the asteroid impact were discovered just below the Cretaceous-Tertiary (K-T) boundary, there was a strong causal link: the effects of the asteroid impact had driven the dinosaurs to extinction.
However, a problem with this theory has come to light. It turns out the Chicxulub impact may pre-date the K-T boundary by 300,000 years…
A number of scientists have disagreed with the theory that the Chicxulub impact caused the death of the dinosaurs 65 million years ago, and this newest research appears to show the two events may not be linked after all.
Gerta Keller of Princeton University in New Jersey, and Thierry Adatte of the University of Lausanne, Switzerland, are set to publish this new work in the Journal of the Geological Society today, using data from the analysis of sediment from Mexico to prove the asteroid impact pre-dated the K-T boundary by as much as 300,000 years.
"We know that between four and nine meters of sediments were deposited at about two to three centimeters per thousand years after the impact," said Keller. "The mass extinction level can be seen in the sediments above this interval."
This means that the mass extinctions appeared to take place a long time after the impact. However, impact-extinction advocates point out that this inconsistency in sediment data is probably down to sediment disruption by tsunamis and geological upheaval immediately after the impact.
According to Keller, there is no indication that this could be the case. Deposition of impact sediment occurred over a huge time period, not the hours or days deposition would have taken if a tsunami affected sedimentary records.
Another problem with the impact extinction theory is that the Chicxulub impact may not have had the radical extinction effect on plants and animals as we previously thought. The researchers found a total of 52 fossilized species that appeared to be happily living before the layer of impact sediment… and the same 52 species appeared to by happily living after the layer of impact sediment.
"We found that not a single species went extinct as a result of the Chicxulub impact." — Gerta Keller
Although this is some very interesting research, sure to turn dinosaur extinction theory on its head, if an asteroid didn't kill the dinosaurs, what did?
Keller points the finger at volcanic activity. Massive amounts of dust and gas was released from eruptions at the Deccan Traps in India 65 million years ago, possibly plunging the planet into a prolonged period without Sun.
Update: With any scientific debate, there are details behind new research that may not be immediately apparent. As Ethan Siegel highlights in a recent ScienceBlogs article (What Wiped Out The Dinosaurs?, April 27th), the evidence for an asteroid impact wiping out the dinosaurs is overwhelming. Just because there appears to be a discrepancy in the location of impact sediment and K-T boundary does not mean the impact-extinction theory is wrong in any way. Keller's research is an interesting investigation, worthy of further study, but this doesn't change the fact that huge global damage would have been caused by the Chicxulub impact. This remains the prime candidate as to why the dinosaurs were suddenly made extinct 65 million years ago.
Source: Physorg.com
Filed under: Asteroids
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April 27th, 2009 at 5:51 am
"What killed the dinosaurs" looks like it is one debate that will continue in parallel with the origin of the universe. What if it took 300,000 years for the dinosaurs to die out? For the amount of time they were around, it doesn't seem implausable. Just as it takes millions of years for evolution to occur, a few hundred thousand years to die out is a small percentage of that time.
April 27th, 2009 at 7:52 am
If memory serves, the K-T rock boundary is defined, in part, by an abundance of the (otherwise) rare element iridium. The iridium is theorized to be from the impacting asteriod. Does Keller's theory account for the Ir at the K-T boundary?
April 27th, 2009 at 8:35 am
I teach astronomy at the University of Maryland. For several years now, I have taught a course focused on collisions between astronomical objects. One topic is impacts on the Earth, especially the K-T impact, so I have read quite a bit about this topic and the on-going debate about the impact.
As soon as I read the headline for this story, I knew that it was going to be based on Gerta Keller's work. Since the impact hypothesis was proposed, Gerta Keller has been a vocal and prolific opponent of it.
This is not a bad thing, as science progresses through the testing of predictions based on hypotheses. At the time the idea of an impact causing the K-T mass extinction was proposed, it was pretty radical, and certainly a lot of evidence would be required to support such a radical hypothesis.
After the hypothesis was proposed, many scientists began scrambling to look for the evidence (or evidence to the contrary). Again, this is a good thing, as long as scientists follow the basic scientific principles of sharing knowledge and results, and only accepting results that are repeatable and confirmed by other scientists.
However, there are several cases (at least) where Gerta Keller refused to share her paleontological specimens with other scientists in order to confirm her results. Using these specimens, she claimed to have evidence that would disconfirm the impact hypothesis. But no other scientists (other than her close colleagues) have been able to confirm her results with other samples, and they have not been permitted to examine hers freely.
A lot of the history of the debate over the impact hypothesis and scientific reaction to it can be found in the book "Night Comes to the Cretaceous" by James Lawrence Powell. This is a fascinating book, that I highly recommended, although it's now about 10 years old and does not include more recent scientific work on the topic.
As a result of her secrecy and disregard for scientific openness, I cannot accept her ideas now, since they seem to be based on the same kind of work. Dr. Keller seems to be extraordinarily good at attracting media attention to her work, but if you notice, very few of the articles written about her work contain any opposing scientific view (which also happens to be the mainstream view).
In the last few years, Dr. Keller has been focusing on the timing of the mass extinction compared to that of the Chicxulub impact crater. In the current article, she argues that the timing doesn't match, but that the timing of a well-known massive volcanic episode is to blame. She has suggested a similar alternative hypothesis in several other news articles I have read. In some articles she suggests that in addition to the volcanism, there might have been a second large impact at about the same time. Those articles DO contain comments by experts on the subject that are not Dr. Keller's colleagues. Here are some quotations from the articles:
- "It [her result] appears to contradict many other lines of evidence that seem rather unambiguously to indicate that the [Chicxulub] crater formed at the K-T boundary." Dr. David Kring of U. Arizona, in a BBC News article from March 2004.
- "That two such impacts occurred within 300,000 years and both hit the Earth at almost exactly the same place is statistically unlikely." Dr. Joanna Morgan, Imperial College, London, in a BBC News article from March 2004.
One of Keller's main arguments is that the layer of debris from the impact that settled to the bottom of the oceans afterward does not match what would be expected for a quick event, but must have accumulated much more slowly. She seems to disregard the possibility that the layer could have been laid down quickly and then altered in the 65 million years afterward, as these scientists suggest:
- "[the burrows in the layer were] made by organisms digging after the fireball layer was deposited." Dr. Alan Hildebrand, in a National Geographic News article, March 2004.
- Dr. Thomas R. Holtz, Jr., from U. Maryland supports the view that the layer was quickly laid down as crater infill, and it's OK that there are Cretaceous fossils in the layer. "If an asteroid clobbered the Eastern seaboard of the US today, I would expect that most of the infilling would be Chevys and Hondas and shopping malls and houses and cows and McDonald's burger wrappers… Only a tiny bit might be mastodons and Clovis points and Miocene whales." From a National Geographic News article, March 2004.
To summarize, Gerta Keller has been pushing her alternate hypotheses to explain the K-T mass extinction for quite some time. However, given her dubious scientific practices in the past, I cannot credit her work until other scientists confirm it. To this point, other scientists working on the topic have NOT done so.
April 27th, 2009 at 10:57 am
The dating is probably flawed. If the Chicxulub meteorite impact didn't wipe out the dinosaurs then what did it do? Allow them to flourish?
April 27th, 2009 at 11:47 am
Yeah, just goes to show that not all new research takes us in the right direction. Perhaps Keller may be proven right in the long run, but it seems more likely that, for whatever reason, she took a turn down a blind alley.
P.S. Is it just me, or are other people finding it impossible to change their newly assigned passwords to something easier to remember — I'm getting an error message from the server when I try.
April 27th, 2009 at 7:11 pm
Thanks, avondale, for some perspective on some of the issues mentioned in the article. After reading several versions of this story at other science sites, I noticed a curious similarity in detail and almost complete omission of some of the phenomena explained by the impact theory (the many, besides the iridium layer evidence, which is pretty strong in its own right). I've seen challenges to the impact hypothesis before, but I was not aware most of these were from a single scientist or associates.
April 27th, 2009 at 10:15 pm
Humans will specuate about the demise of the dinosaurs until the human race becomes extinct. Undoubtedly, there will eventually be more findings but the total true answers may never be known. One thing that is certain, if dinosaurs here, no humans!!!! I wonder how much the smartest dinosaurs would've evolved over 65Million more year, -still, I doubt dinosaurs would be as resourceful or productive as humans!!
April 27th, 2009 at 10:43 pm
I Know it was the Swine Flu
April 27th, 2009 at 11:27 pm
See, if these were lawyers, they'd each be blaming the other guy…
And yet the geophysicist says "a volcano did it", and the astronomer says "an asteroid did it"…
This is what's so nice about science… Whatever it was, it killed off most of the biosphere, and yet each scientist is actually standing up and accepting, no, even demanding! full responsibility…
Very commendable indeed.
April 28th, 2009 at 1:20 am
Aren't the Deccan Traps in India more or less directly opposite from the Chicxulub impact site?
April 28th, 2009 at 3:12 am
Avondale, that's really useful to know: I thought I'd heard a version of this particular idea before.
April 28th, 2009 at 4:52 am
@avondale
Quite an informative post there. Thank you for bringing some of the information to light and for answering some of the questions I had about the discrepancies.
I read this article title in my google reader and then went off to Starts with a Bang to see what was going on and was a little confused about the two Ideas.
For the first time ever the comments section actually cleared things up for me instead of making me want to /wrists.
April 28th, 2009 at 9:55 am
Reading the answers, enormous volcanic fields in India, Chicxulub impact crater both causing atmospheric,land and water pollution problems all make sense and to me appeared to happen in unison. in a sequence IMHO, may be extremely diffictult to prove or disprove. In a macabre way of thinking, to get it perfectly correct, another type hugh asteroid/comet hits the Earth with the same effect 65Million years ago and still living scientists records the sequence of death and destruction on objects(marble,human created non-warping objects, other harden objects to preserve writtings and artwork before the human race is wiped out. The true cause of what happened 65Million years ago will be answered!!!! However, should any 'mad' scientist' gets very hung up to prove his point and wish for a repeat performance of 65million years ago, I believe level headed scientist and I will hunt this person down and give the person far, far more than a lecture (no need to say)
lol
April 28th, 2009 at 11:35 am
I am not a scientist, although my career ended in Info tech-Network Administration, however, I am a serious amateur astronomer and a earth science researcher most of my life. I've read a book some time back ' Agents of Chaos-Stephen Harris-Mountain Press Publishing Co.-to the great Earth Scientists who posts through this site, the Duccan fields has been explained, the book said perhaps the 'hot spot' for the Hawaiian chains may be caused by a rock from the sky that's taking about 100Million years to heal, however, reading other sources tells me there are many 'hot spots' in the Pacific Ocean so I said to myself the dynamics of the Earth caused Hawaiian 'hot spot' , the book says the Yellowstone Hot Spot was caused from above hiting the western edge of the N. American plate and destroyed that part of the plate , created the huge 'runny' Columbian Lava Fields lava field but still smaller than Duccan- but after reading other source, I say the Yellowstone hot spot is a continuum that
started like a oceanic ' hot spot' , and the N.American plate moved over it and now has magma of an extemely explosive nature.
My puzzle is, what caused the Columbian Lava Fields to be so large and "'runny"' for so long despite reacting with a continental plate that should have changed the composition of the magma to violently dangerous?
It is interesting how the Earth itself can be an exterminator of most of life, perhaps with much help from above but this is beyond my knowledge.
April 28th, 2009 at 11:40 am
Very nice to be able to enjoy the comments again, yes.
Thank you, avondale (and UT for introducing a comment policy).
April 28th, 2009 at 4:31 pm
Iridium is not that rare deep inside the Earth, which is exactly where the stuff of volcanos originates. Several big volcanos blasting debris high into the atmosphere could easily deposit iridium around the earth, as also could one K-T impactor.
Consider too the fact that dinosaurs are related to birds. Viruses have been around for hundreds of millions of years, maybe much longer. That's plenty of time for ancient "bird flus" to have decimated the dinosaur family. Throw in the random asteroid impact, and coat it all with vast amounts of vulcanism. So what's a fun loving dinosaur to do, but die?
April 29th, 2009 at 3:08 pm
The Deccan Traps in India ARE exactly opposite the crater and some geologists have suggested that the impact caused the magma to "bulge" creating volcanic activity that lasted for thousands of years. The latest programs I've seen have shown that the dinosaurs were already well on their way to extinction before the impact anyway, and that the impact and volcanic activity (along with the existing severe climatic changes) pushed the Dinos over the edge for good.
I do not believe that any one event could have killed off so much. Think about it…..
" The impact killed off everything that was over 55 pounds" ????
- the fossil record shows less dinosaurs found for the 10 million years leading up to the KT boundary anyway……….
I think ol' GERTA is hungry for attention, research money and she has to justify her existence in some way. She's just kind of sad, really!