Geoscientist offers new evidence that meteorite did not wipe out dinosaurs

Princeton geoscientist offers new evidence that meteorite did not wipe out dinosaurs
Much of the new data comes from a trench dug out of low-lying hills in northeastern Mexico at a site called El Peñon. A group of Princeton undergraduates, including Richard Lease (left) and Steven Andrews (right), accompanying Princeton Professor Gerta Keller on a field trip to Mexico in 2004 excavated the area and uncovered the new evidence. Keller and her team have been analyzing that evidence for the last several years. Credit: Photo: Courtesy of Gerta Keller

A Princeton University geoscientist who has stirred controversy with her studies challenging a popular theory that an asteroid wiped out the dinosaurs has compiled powerful new evidence asserting her position.

Gerta Keller, whose studies of rock formations at many sites in the United States, Mexico and India have led her to conclude that volcanoes, not a vast meteorite, were the more likely culprits in the demise of the Earth's giant reptiles, is producing new data supporting her claim.

Keller, a Princeton professor of geosciences, and several co-authors lay out the case in a paper published April 27 in the Journal of the Geological Society of London. Examinations at several new sites have produced "biotic evidence" -- the fossilized traces of plants and animals tied to the period in question -- indicating that a massive die-off did not occur directly after the strike but much later.

In addition, Keller and other researchers have found "aftermath" sediments that remained undisturbed and showed signs of active life, with burrows formed by creatures colonizing the ocean floor. This would quash a theory advanced by some that a massive tsunami followed the impact, Keller said.

"Careful documentation of results that are reproducible and verifiable will uncover what really happened," Keller said. "This study takes an important step in that direction."

Much of the new data comes from a trench dug out of low-lying hills in northeastern Mexico at a site called El Peñon. A group of Princeton undergraduates accompanying Keller on a field trip to Mexico in 2004 excavated the area and uncovered the new evidence. Keller and her team have been analyzing that evidence for the last several years.

Understanding what caused the to disappear remains a great mystery. Theories attempting to explain it include asteroid or cometary impacts, volcanoes, , rising sea levels and supernova explosions. Scientists know that at a point about 65 million years ago, some phenomenon triggered mass extinctions on the land and oceans.

This event defines the boundary between the older Mesozoic Era, the "Age of Reptiles," and the modern Cenozoic Era, the "Age of Mammals." On a finer geological scale, the disappearances occurred between the Cretaceous (K) period and the Tertiary (T) period. As a result, scientists refer to this time as the K-T boundary.

At many locations, the K-T boundary is clearly visible in rock formations, which contain a thin layer of clay rich in the element iridium. Because iridium is more common in asteroids and comets than on Earth, scientists proposed in 1980 that an asteroid or comet must have struck Earth just at the boundary and caused the mass extinction of dinosaurs and many other animals. They thought they had found the culprit when they discovered the Chicxulub impact crater in Mexico's northern Yucatan.

Keller began studying the K-T boundary in 1984 -- the year she arrived at Princeton. She discovered that the evidence for the asteroid theory was not so clear. In field investigations, she and her team of students and collaborators found populations of Cretaceous age foraminifera, one-celled ocean organisms that evolved rapidly during select geological periods, living on top of the impact fallout from Chicxulub. The fallout from the asteroid that struck Chicxulub is visible as a layer of glassy beads of molten rock that rained down after the impact. If this impact caused the mass extinction, then the foraminifera above the impact glass beads should have been the newly evolved species of the Tertiary age.

Using these fossil remains to construct a timeline, she and her team were able to date the surrounding geologic features and begin to piece together proof that the impact occurred 300,000 years before the great extinction.

Over the years, Keller's group has amassed evidence for as many as four major events widely separated in time in that area of Mexico as well as in Texas. The oldest of the four events is the Chicxulub impact, seen by the fallout of glass beads. The second is about 150,000 years later and seen in a layer of sandstone with Chicxulub impact glass beads that were transported from shallow shore areas into deep waters during a sea level fall and was commonly interpreted as a tsunami generated by the Chicxulub impact. About 100,000 to 150,000 years later, the third event struck at the time of the K-T boundary with its iridium layer and mass extinction. This event may represent a second large impact or massive volcanism. The fourth event is possibly a smaller impact as evidenced by another iridium layer about 100,000 years after the mass extinction.

Advocates of the Chicxulub impact theory suggest that the impact crater and the mass extinction event only appear far apart in the sedimentary record because an earthquake or tsunami caused slumps and mixing of sediments surrounding the Gulf of Mexico. To date no evidence of major disturbance has been found in the sediments.

Keller says her team's newest research, however, confirms what she has found in earlier studies -- that the sandstone complex that overlays the impact layer was not deposited over hours or days by a tsunami but over a long time period. From El Peñon in and other sites listed in the new study, the scientists were able to calculate that between 13 and 30 feet of sediments were deposited at a rate of about an inch per thousand years after the impact. These sediments separating the impact layer from the sandstone complex and the overlying mass extinction were formed by normal processes. There is evidence of erosion and transportation of sediments in the sandstone layers, but no evidence of structural disturbance, Keller said.

Also at El Peñon, the researchers found 52 species present in sediments below the impact layer and counted all 52 still present in the layer above it, indicating that the impact has not had the devasting biotic effect on species diversity as has been suggested. "Not a single species went extinct as a result of the Chicxulub impact," Keller said.

In contrast, she noted, at a nearby site known as La Sierrita where the K-T boundary, iridium anomaly and mass extinction are recorded, 31 out of 44 species disappeared from the fossil record at the K-T boundary.

"Keller and colleagues continue to amass detailed stratigraphic information supporting new thinking about the Chicxulub impact and the mass extinction at the end of the Cretaceous," said Richard Lane, program director in the National Science Foundation's division of earth sciences, which funded the research. "The two may not be linked after all."

Keller suggests that the massive volcanic eruptions at the Deccan Traps in India may be responsible for the extinction, releasing massive amounts of dust and gases that could have blocked sunlight, altered climate and caused acid rain. The fact that the Chicxulub impact seems to have had no effect on biota, she said, despite its 6-mile-in-diameter size, indicates that even large asteroid impacts may not be as deadly as imagined.

She regards the latest evidence as sufficiently convincing and compelling to allow her to move on and investigate further the evidence for Deccan volcanism as being at the root of dinosaur extinction. But she does not expect her teams' present work will stop the raging debate at the heart of this controversy.

"The decades-old controversy over the cause of the K-T will never achieve consensus," Keller said. But consensus, she added, is not a precondition to advancing science and unraveling truth. "What is necessary is careful documentation of results that are reproducible and verifiable," she said.

Source: Princeton University

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May 04, 2009
Deccan volcanism was caused by the shock wave from the Chicxulub impact. The Deccan area was on the exact opposite side of the earth during the impact. This has been known for many years but you do not hear many scientist take about it. The huge area of magma then simmers for a few hundred thousand years sending all
sorts of gas and eruptions into the atmosphere.

May 04, 2009
Are you saying that it took 300,000 years for the shock wave from Chicxulub to transmit through the planet to the Deccan flats?

May 04, 2009
It is well known that both the Deccan and Siberian flats of magma spewed gas and other material for tens of thousands of years. This led to the decline of dinosaurs. These flats covered thousands of square miles. The Siberian flats were caused by the other great impact. You can see flats on the moon on the opposite site of major impacts. This is not rocket science. Just hit one side of a water balloon and watch the shock wave.

May 04, 2009
Of course both of these flats were active for a considerable time,but what I asked was
"Are you saying that it took 300,000 years for the shock wave from Chicxulub to transmit through the planet to the Deccan flats?"

May 04, 2009
Any shock of the magnitude of Chicxulub would set off every volcano on earth that was primed to erupt. If the dating for survival times proves out (I do not see how it could) then maybe but until then Deccan should be considered as a possible persistent ancillary effect.

May 04, 2009
It would appear that the item above is suggesting that there is a gap of 300,000 years between the Chicxulub event and the outpouring from the Deccan Flats.As Avitar suggests this activity at Deccan was a persistent event and may have been triggered by whatever caused the Shiva crater which is right next door.

May 04, 2009
The lethality of an impact event probably depends (asides from its mass) on various factors such as whether the impact was on a land or ocean, the thickness of the Earth's crust at the impact point as well at its antipodean point. If the impact point was in the ocean, and the antipode was on a land where the Earth's crust was thick, it probably would not have caused a major extinction event.

The massive, nearly 30,000-year long, volcanic eruptions at the Deccan Traps most likely contributed more to the Cretaceous-Tertiary (K-T) extinction than the Chicxulub asteroid itself, but it is possible that Chicxulub impact was the cause of the Deccan Traps eruptions which was at the antipode of the Chicxulub impact point 65 million years ago in a spot where it was directly above one of Earth's crustal hotspots. The antipodal force of the impact ripped Earth's crust open and exposed hot magma that continued to erupt for tens of thousands of years, thus causing a global climatic catastrophe that led to the K-T mass extinction.

As to the purported lag of 300,000 years between the Chicxulub impact and the great extinction, Ms. Keller, unfortunately, is vague on details whether the extinction happened exactly at 300,000 years after the impact, or that the last dinosaur died at that point after its relatives and ancestors had been dying for 300,000 years, possibly as a consequence of the climatic catastrophe triggered by the Chicxulub impact.

We have to look at asteroid impacts as though they are bullets striking at, say, a human body. Not every bullet wound on the body is lethal; in fact, if serious infections due to the wounds are ruled out, only the bullets hitting the vital organs or arteries are lethal, as the body would bleed to death. So for an asteroid to be the trigger for a major extinction, it had to be "lucky" to hit the part of the earth that can trigger a massive "bleeding" in the form of volcanism, which in turn would cause prolonged climatic catastrophe.

The way I would envision the whole K-T extinction in a nutshell is that the Chicxulub impact itself did kill approximately two-third to three-quarter of the dinosaur population with the effects of the initial impact. The surviving population gradually died off as the accumulative effects of the 30,000-year long Deccan-Traps volcanic eruptions altered Earth's climate to the point that when the eruptions stopped, the climate was no longer favorable to the gigantic dinosaurs that we humans usually associate dinosaurs with. I would suspect that most of the fossilized remains of dinosaurs that lived near the end of that 300,000-year period after the Chicxulub impact, if Ms Keller claim is correct, are rather small in size compared to those that thrived before the Chicxulub.

But 300, 000 years is a long period of time, and some dinosaurs must have progressively evolved to adapt to a new climate by downsizing, and those that succeeded essentially became the ancestors of today's birds.

We are not certain if Earth is still capable of massive basalt floods of the size of Deccan Traps, not to mention the Siberian Traps--a far larger one, at this stage of Earth's geological transformation. Undoubtedly they were quite common in earlier periods of Earth's history, but Earth internally has been steadily cooling down since. In fact, we know from the prehistoric eruptions of the Yellowstone supervolcano--one of the largest supervolcanos still thought to be active--that, as massive as those eruptions and consequent basaltic floods had been, they cannot compare to those of the Deccan and Siberian Traps eruptions in size and duration.

I personally do not think that Earth has been capable of basalt floods of the magnitude of Deccan and Siberian Traps for at least half a billion years on its own unless they were helped by impacting asteroids large and "lucky" enough to hit the right spot (thin crust on a land, not ocean, near Earth's crustal hotspots) that in turn caused extensive crustal ruptures, triggering basalt floods that would take Earth tens of thousands of years to plug up.

In this regard, mass extinctions had been, regrettably, the consequence of Earth trying to heal itself.

May 04, 2009
Nope this is all wrong, Jesus did it.

May 04, 2009
Ask Al Gore.. He has all the answers!

May 05, 2009
Interesting post DrS,just one question to ask.What if an asteroid had smacked into India and caused the eruption? It is possible that several lumps of a worn out comet struck within a short timeframe.

May 05, 2009
I am not an expert in ballistic science, but I would suspect that the crustal fractures created by the impacting object at it's collision point is not as catastrophic as at its antipodean point, as the force converging at the antipodean point would thrust the Earth's crust upward, rather than downward.

Thus, had the Chicxulub asteroid struck the proto-Indian subcontinent directly (a chunk of continent drifting in the ocean at the time), I don't think it would have resulted in the basaltic flooding that created the Deccan Traps.

A substantial portion of the global dinosaur population still would have perished as the result of the immediate effects of the impact, with those dinosaur species closest to the impact point most affected--even completely wiped out, but there would have been enough other species left to recover within a few hundred thousands years.

I would say it is the Earth's continual "bleeding" after the Chicxulub impact that prevented the recovery of dinosaur population and subsequently brought the end to the age of dinosaur.

May 05, 2009
Dr. S, excellent points. Thanks for taking the time to write that.

May 05, 2009
Any shock of the magnitude of Chicxulub would set off every volcano on earth that was primed to erupt. If the dating for survival times proves out (I do not see how it could) then maybe but until then Deccan should be considered as a possible persistent ancillary effect.

May 07, 2009
It might have shaken things up so badly that the deccan volcanoes erupted 300,000 years later. The shock waves were focused onto the opposite side of the earth. It might have taken that long for the shock wave induced damage to affect already ongoing processes like uplift of the Himalayan plateau and subduction to cause the volcanic effects, later.
300,000 years is not along time geologically and there seems to be a cause and effect relationship between the Deccan volcanoes and the asteroid impact.

May 07, 2009
I'm yet to be convinced that an impact at one point of the Earth would cause a tearing of crust at its antipodes.

Unlike a balloon, the Earth does not have a very elastic skin. Unlike the Moon, the Earth's crust is composed of plates at whose subduction boundaries the shock wave would be dispersed (I guess).

May 08, 2009
Sorry to be a bit stubborn on this but I'm still not convinced.
As far as the association with the Deccan Traps are concerned I googled this-

"Is there evidence of ancient volcanic activity at the antipode of Chicxulub? Early speculation centered on the Deccan Traps, a basalticplateau covering much of India that was formed over a few millionyears roughly around the time of the impact. But scientists havevirtually eliminated that possibility. Taking continental drift intoaccount, they estimate that what is now India was 1,000 miles or moreaway from where the Chicxulub antipode was 65 million years ago. Andthe location antipodal to the Deccan Traps at the time of theirformation is now on the floor of the eastern Pacific Ocean. Becausethe ocean floor moves like a conveyor belt, rising to form ridges anddiving back into the earth in a process called subduction, Hagstrumsays, ``half of the ocean floor has since disappeared'' and evidenceof an antipodal impact ``would be on that half.''"

The only reference to NASA's gun experiments I could find was limited to concentration of ejecta at the antipodes-

May 08, 2009
Waves can transmit through boundaries easily (otherwise, you won't be able to see anything through a glass of clear water), although there might be refractions and delay due to such boundaries. The reason that the actual antipode might not have been at the exact mathematical antipode of the Chicxulub impact point might be due to the asymmetrical effect produced by the transmission of the shockwaves through such boundaries.

The fact that the proto-Indian subcontinent afloat at the impact time was within 1,000 miles of the exact antipode can be construed to imply tantalizingly the possibility of such an asymmetry.

Seismic shockwaves caused by the impact travel at a tremendous speed: if there is fraction of a second delay in a sector of the converging waves, it might shift the convergence point (antipode) by few hundred miles or more. That's my intuitive guess. Needless to say, those who make living out of this sort of thing have the time, the appropriate mathematics, and a super-computer to do the actual calculation.

May 09, 2009
I think that you're right about the effect being offset from the exact antipodes for something that's as irregular as the Earth. What I don't get though is, is this effect a surface effect or something deeper or both?

Intuitively I would guess that the non-surface shock wave travelling through the depths of the planet would be dispersed totally.
If the effect is purely transmitted across the surface then surely as soon as the shock wave came to a subduction boundary most of the force would get transmitted down into the depths of the planet and again get dispersed. The shock wave may well be transmitted through other types of boundaries (even the sea-floor spreading type) but with the loss of some of the shock wave due to subduction there will be no concentrated exact focus in region of the antipodes.

May 10, 2009
In order for the subduction plate to carry all the seismic waves it is carrying safely away from the adjacent, top-laying plate, there must be a layer of sufficient thickness (several miles will do) between the plates that consist of either air or vacuum. This has not been experimentally observed.

Furthermore, if the seismic waves on a subduction plate are actually being steered away from the adjacent plates, then the seismic waves generated by a tectonic event (earthquake, A-bomb test) on a plate near a plate boundary would not be transmitted over to the adjacent plate, thus depriving the US Geological Survey and National Security Agency much of their ability to detect such even across the globe.

In reality, the top plate is in intimate contact with the bottom subduction plate, and that is why there is so much heat generated in the subduction zones that contributes to the enhanced geological activities in those tectonic plate boundaries, such as birthing of volcanoes.

May 10, 2009
I maintain that nearly all of the shock wave will not get transmitted to a plate which overlies the subducting plate. Even seismometers have trouble picking up signals across such a boundary, as this quote implies-

"California earthquakes are born in the constant shoving match between the North American plate, which we live on, and the Pacific plate, which dives under the ocean and stretches westward toward Asia. Virtually all our earthquake data comes from sensing shudders in the North American plate.
To learn about the Pacific plate%u2019s side of the story, MBARI installed a seafloor seismometer [...]. Buried in the seafloor west of the San Gregorio fault, the sensor sits on the far western side of the entire San Andreas fault system."


May 11, 2009
This "Shock Dynamics" website you've quoted has quite an interesting new theory of geology, provided you don't have a prejudice against its creationist intentions. From the subtitle of the site-
"A new geology theory featuring impact-powered rapid continental drift as an alternative to plate tectonics.
The key to creation geology."

May 11, 2009
Here is essentially what happened:

The physical (as slightly differentiated from mathematical) antipodean point of the Chicxulub impact point was probably located approximately four to five hundred miles north (14 degrees south by 65 degrees east) of the eastern tip of the present day Rodriguez undersea ridge when the Chicxulub object plummeted on the other side of Earth 65 million years ago.

The massive fracture lines caused by the antipodean convergent force sliced off a sliver of the proto-Indian subcontinent running north-south from the western side of the proto-subcontinent; thus creating the present day Seychelles microcontinent. The crescent shaped ocean trench west of the Seychelles island group was probably the western rim of the circular fracture zone. (Its present day location is about 1,000 miles to the west of the antipodean fracture zone due to the spreading of the Carlsberg and Central Indian Ocean ridges.)

The existence of the Lakshadweep-Chagos underwater ridge that seems to trace the position of the Deccan Traps as the proto-subcontinent continued to move northward after the impact event indicates that the crustal hotspot created by the antipodean force uplifting the Earth's crust continued to remain active for tens of millions of years beneath the subcontinent.

This leads to the possibility that the Deccan Traps continued to erupt for hundred of thousands of years, possibly even for a few million years, rather than the generally accepted estimate of 30,000 years. However, in the later phase of the volcanic activities, it was probably comparable to the level of volcanic activities observed today in the Hawaiian island volcanoes.

Thus, it is quite likely that the most lethal part of the eruptions that probably resulted in the Cretaceous-Tertiary (K-T) extinction was still compressed into the first 30,000 years or so, with residual volcanism continuing for far longer period of time.

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