New Blow for Dinosaur-Killing Asteroid Theory

New Blow for Dinosaur-Killing Asteroid Theory
This artist's rendering shows the Chicxulub crater at the time of the meteorite's impact. Credit: NASA

( -- The enduringly popular theory that the Chicxulub crater holds the clue to the demise of the dinosaurs, along with some 65 percent of all species 65 million years ago, is challenged in a paper to be published in the Journal of the Geological Society on April 27, 2009.

The crater, discovered in 1978 in northern Yucutan and measuring about 180 kilometers (112 miles) in diameter, records a massive extra-terrestrial impact.

When spherules from the impact were found just below the Cretaceous-Tertiary (K-T) boundary, it was quickly identified as the "smoking gun" responsible for the event that took place 65 million years ago.

It was this event which saw the demise of dinosaurs, along with countless other plant and animal species.

However, a number of scientists have since disagreed with this interpretation.

The newest research, led by Gerta Keller of Princeton University in New Jersey, and Thierry Adatte of the University of Lausanne, Switzerland, uses evidence from Mexico to suggest that the Chicxulub impact predates the K-T boundary by as much as 300,000 years.

"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," says H. Richard Lane, program director in the National Science Foundation (NSF)'s Division of Earth Sciences, which funded the research. "The two may not be linked after all."

From El Penon and other localities in Mexico, says Keller, "we know that between four and nine meters of sediments were deposited at about two to three centimeters per thousand years after the impact. The mass extinction level can be seen in the sediments above this interval."

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 of earthquake or tsunami disturbance that resulted from the impact of the asteroid.

"The problem with the tsunami interpretation," says Keller, "is that this sandstone complex was not deposited over hours or days by a tsunami. Deposition occurred over a very long time period."

The study found that the sediments separating the two events were characteristic of normal sedimentation, with burrows formed by creatures colonizing the ocean floor, erosion and transportation of sediments, and no evidence of structural disturbance.

The scientists also found evidence that the Chicxulub impact didn't have the dramatic impact on species diversity that has been suggested.

At one site at El Penon, the researchers found 52 species present in sediments below the impact spherule layer, and counted all 52 still present in layers above the spherules.

"We found that not a single species went extinct as a result of the Chicxulub impact," says Keller.

This conclusion should not come as too great a surprise, she says. None of the other great mass extinctions are associated with an impact, and no other large craters are known to have caused a significant extinction event.

Keller suggests that the massive volcanic eruptions at the Deccan Traps in India may be responsible for the extinction, releasing huge amounts of dust and gases that could have blocked out sunlight and brought about a significant greenhouse effect.

Source: National Science Foundation (news : web)

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More Than a Meteor Likely Killed Dinosaurs 65 Million Years Ago

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Apr 27, 2009
Shameful that this impact crater theory has basicly been taught as "science fact" in middle schools and high schools for three and a half decades.

Apr 27, 2009
Dude, that's science. This is why "science fact" is always referred to as "theory." Scientists come up with the best theories they can given the available evidence. As new evidence is discovered, new theories are made. No scientist has ever claimed to perfectly understand the way the world works.

Apr 27, 2009
"...None of the other great mass extinctions are associated with an impact, and no other large craters are known to have caused a significant extinction event..." Well that's certainly good to know. I was beginning to be afraid that the asteroids "would get me if I don't watch out"...Now with the pronouncements from these two, I no longer have to worry about asteroid impacts...No Worries, Mate.

Apr 27, 2009
me thinks these scientists are playing in their sandbox. extinctions happen over millions of years with many conspiring causes . the problem with looking for a "smoking gun" is that often there are many guns with their smoke and sound long gone .

keep it in perspective . 300,000 years is within 0.5% of the 65 million year old extinction . the reality is fuzzier than the numbers . a force of 1 million atomic bombs within 300,000 years of the fuzzy event - is a major smoke of a gun.

Apr 27, 2009
This could be bad news. There are reasonable ways to deflect an asteroid ... but who knows how to prevent huge volcanic eruptions?

Apr 27, 2009
maybe the impact caused a long term effect that caused the mnass extibnction 300,000 years later. It might have taken that long for conditions to develop.

Apr 27, 2009
Shameful that this impact crater theory has basicly been taught as "science fact" in middle schools and high schools for three and a half decades.

Same for Manmade Global Warming.

Apr 27, 2009
Many impact events happened during the time that life existed on Earth, but major extinction events were rare during those times. So how did some impacts cause major extinctions but not others? The answer depends, first of all, on the mass of the impact object, but also on how the impact occurred, and how the earth's crust reacted to the impact.

The lethality of an impact event should depend (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 the Earth's crustal hot spots. The antipodal force of the impact ripped the 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.

Apr 27, 2009
Doctorserendipitous is exactly right. When you look on the moon there is always a large area on the opposite side from where a large impact hit that is disturbed. This has been known for many years but you never hear many people talk about it. If the conditions are right at the antipode (thin crust etc) then you will have amassive crust disturbance such as you find in India at the Deccan traps and also in Siberia from the other great meteor impact. Just tap one side of a water balloon and watch the shock wave
reach the other side.

Apr 29, 2009
It is interesting that the KT boundary is no longer associated with this particular impact event.
It was the association of the KT boundary with the impact event that caused me to question the impact as a cause of the extinctions.
Because had the two been related then some dinosaur remains, especially those of the larger dinosaurs should have protruded through the KT boundary or at least have had the KT boundary deposit directly in contact with their fossilized remains.
But all such fossils had been found below the KT boundary.
This meant there was a time gap between the death of the animal and the laying down of the KT boundary.
Rather than seek a one off event as a cause I think it would be more productive to look at processes of change. Certainly some of these processes may have been triggered by specific events but the more probable causes are a gradual change in climate and a progressive change in plant life.
Once the food source expires and the animal is not able to adapt to the new forms of plant life the species will soon die out. With no herbivores to eat the carnivores will soon follow them into extinction.
If our present concerns over global warming are as accurate as some would have us believe then we will soon bear witness to this actually happening with many species, some due to temperature changes, some due to loss of habitat, some due to loss of food sources etc., but all related to or caused by global warming.
Our next 20 to 30 years will be very interesting.

May 03, 2009
Chicxulub = tipping point

Jul 29, 2009
A new theory about

Extinction of Dinosaurs

The theory of the increasing of the earth's gravity

From the earliest days that the big bones of past animals were found, some questions about their decline came up, which continued up to this day. By observing the fossils of giant dinosaurs, about several million years ago, this question comes up that, which factors caused them to decline?

Scientist has made many efforts to answer this question, and they suggested many theories in this case. Theories like the outbreak of diseases, decreasing food and eating of their eggs by other smaller mammals.

Among these theories, there is one theory which is of more acceptance for scientists and attracts the attention of more acceptance for scientists and attracts the attention of most people, this theory which came up by two American geologists from California%u2019s university (Berkeley), Luis Alvarez and his son Walter at recent years of seventh decade, is about the collision of meteorite with earth. This theory says that: A rock with 10-15km diameter and about one thousand billion ton weight, with 150 thousand km/h entered earth's atmosphere and friction of this giant rock on the air caused the sublimation of its outer layers. Four or five seconds later the big core of this big meteorite collided the surface of sea and made a big wave with height of 1km. This wave was distributed on the oceans and cover seashores. Collision of meteorite sent a mixture of steam and dust and stones on the earth. All of these stems, smokes and dusts made a big curtain on earth and for several months or perhaps years the earth was in an absolute dark. These events occurred about 65 million years ago and declined dinosaurs.

If the decline of animals was related to a special period, it was possible to rely on this theory, but as we knew, animals at every time, have lost some species. Perhaps, at one time, these declines were very much, but in any case, declines were existed at every periods of time. If we accept that the collision of a giant meteor it with earth and formation of dust and smoke in 65 million years ago caused the decline of dinosaurs, how we can explain of Endocras with 4.5m diameter, about 500 million years ago. At that time did a giant meteorite collide with earth and declined them? Did another meteorite collide with earth 330 million years ago and declined Eogyrinus? Did the collision of meteorite, about 250 million years ago caused big insects to decline? In this case how we can explain the decline of Lepidodendrales plant, Calamitales and giant tree ferns. Did they was destroyed when a big meteorite collide the earth 300 million years ago. The decline of Macropustion and big Diprotodon in Australia, and decline of the awful bird, Phorohacos, which had a head as big as a horse's and length of 3/6m and big beak of 60cm, about 40 million years ago was because of the collision of meteorite? Did the decline of giant Dinornis maximus and Aepyornis maximus in these years was because of the collision of the big meteorite?

All of these shows that, such a theory can not explain declines animals during the long years. But there is another question, which shows the voidance of this theory! The question is that: assume that the big meteorite collide the earth 65 million years ago, and declined the big dinosaurs, why the remained reptiles couldn%u2019t get bigger. The earliest reptiles, which were amphibious, were very small, but they could get bigger and made the dinosaurs. With the collision of didn't meteorite, dinosaurs was destroyed, but some of small reptiles survived. Why they make bigger animals!

Then, it becomes clear that, the factor, which caused them to decline, is still remained and doesn%u2019t allow big reptiles to get bigger.

So, the collision of the big meteorite with earth and the formation of dust and smoke in atmosphere can not be supposed as the factor of dinosaurs' decline, because, that collision occurred at that time and the effect of dust and smoke have been disappeared and there was no later effect on animals.

Although the theory of the collision of the big meteorite and the formation of dust and smoke can not explain of the animals, but, at the same time, scientists hadn't made a mistake by suggesting this theory, in fact they are close to reality. Because in fact, decline of animals is some how related to meteorites, but not in a way that Luis Alvarez and his son explain.

The theory of the increasing of the gravity says that the fall of meteorites in long periods of time caused the gradual increase of earth, and by increasing of the gravity the ability of blood system of these animals decreased gradually. So those animals which had weaker blood system become smaller or declined. For this reason, after decline of dinosaurs, other reptiles couldn't get bigger, but small mammals which get stronger blood system were able to get their bodies bigger and made the big mammals of 20 million years ago. So, we see that, the scientists are not wrong, and they are right in thinking meteorites as an important factor in this phenomenon. But in the way of explaining and the quality of the extion of the meteorites, they are wrong. Scientists are looking for a big meteorite, which have been able to from such great dust and smoke on earth. But as we know it is not necessary to find a big meteorite, and small meteorites can also increase the gravity provided that their number is large.

People, who accept the theory of the collision of a big meteorite with earth, think that by revivaling the existing genes in the remained eggs of dinosaurs they can rebuild them, or by using the sperms of frozen Mammoth they can rebuild them. They think that the decline factor, which was the big meteorite, collided at the time and everything is finished, and they can form new giant animals. These scientist are unaware of the earth which they put their foots on it, and they don't as far the gravity of earth is like the gravity this time, it is impossible to revival such giant animals.

Ramin Amir mardfar


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