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Chicxulub event
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Startling new evidence from boreholes drilled into the 120-mile-wide Chicxulub crater in Mexico indicate that the great impact, happened 300,000 years too early to have been the one that wiped out the dinosaurs.
The discovery comes at a time when some geologists are convinced that the Chicxulub event killed 70 percent of living species at the Cretaceous-Tertiary (K-T) boundary, 65 million years ago.

Several lines of geological evidence from Chicxulub make a compelling case for the crater having been formed too early to be the mass killer.
Evidence, broken `breccia` rocks, from a borehole, Yaxcopoil 1, was expected to provide final, irrefutable confirmation of Chicxulub's role in the K-T boundary mass extinction. It didn't.
On top of the impact breccia is about two feet of gently-laid-down, thinly layered seafloor mud built up over 300,000 years, Keller said. Those two feet of post-impact mud have the fossils, carbon isotopes and magnetic signal of the late Cretaceous, before the mass die-off.
It's 300,000 years too early.


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Also missing from the Yaxcopoil 1 borehole rocks is any significant iridium signal , the extraterrestrial element that first clued scientists into the fact that an asteroid might have caused the K-T extinctions.
In theory, only massive impacts can distribute the element globally.

As to what really caused the K-T mass extinction; it was probably another asteroid impact combined with intense volcanic activity., and, many dinosaur researchers suspect that dinosaurs were on the decline before the final mass extinction.
Chicxulub might have played a role in their extinction. But a second impact, still undiscovered, might have been the terminal blow.

Keller does not dispute that a meteorite could have helped trigger the demise of the dinosaurs. But she remains confident that Chicxulub is not the crater scientists should be looking at, based on sediments she has analyzed from various Chicxulub sites.
A big collision can also produce another kind of layer, too, by melting and vaporizing silicate rocks, which then condense into sand-grain-size glass spheres known as micro tektites. Depending on the mass of the colliding meteorite, these tiny glass spheres can be thrown hundreds to thousands of kilometres from the point of impact.
Keller discovered that the original Chicxulub micro tektite layers lie up to 14 meters below the KT iridium layer at the north-eastern Mexico site (the crater itself extends from the north-western tip of the Yucatán Peninsula into the Gulf of Mexico).
"To date, no one has found iridium associated with Chicxulub".
Jan Smit, a palaeontologist at Vrije University in the Netherlands, doubts Keller's claims, stating that her argument about KT iridium and Chicxulub borders on tautology: "If you uncouple all the iridium-enriched ejecta layers from the Chicxulub impact, then of course there is no iridium associated with Chicxulub…How and where do you hide the iridium from a large impact such as Chicxulub?"
Keller hypothesizes that the object that made Chicxulub may have been "a dirty snowball" type that did not have any iridium. Some meteorites do not. Another possibility could be that measurements may not yet have been taken from the correct rock strata.
Researchers have also raised doubts about Keller's proposed 300,000-year age difference between Chicxulub and KT, which is based on sedimentation rates extrapolated from the distance between the micro tektite layer and the KT boundary layer. Geoffrey Garrison, a palaeontologist from the University of Washington, wonders why the material separating the two layers could not have been just sediment that was resuspended by the impact and that had simply settled back to the seafloor.
Keller insists that she has already ruled out resuspension. She claims that sediment settling after a high-energy event, such as an impact, tsunami or storm, produces identifiable layers. Heavier grains settle out first, followed by the finest-grained muds and clays.
Such a pattern does not appear in the Chicxulub crater, Keller reports.
Keller plans to bolster her case with an upcoming paper that argues that meteorite impacts that leave Chicxulub-size craters and smaller cannot by themselves cause significant species extinctions. The amount of material ejected, she finds, is insufficient to trigger long- lasting climatic or geographic changes from fire or floods. Sudden mass extinctions might require the coincidence of major volcanism and a large impact event, "but so far no one has found the source crater," Keller says in her dismissal of Chicxulub. "The history of mass extinctions seems to indicate that a single short-term shock to the environment can be survived by nearly all species."

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The Chicxulub Debate
US palaeontologist amasses data against Mexican crater hypothesis.

The widely held theory that a particular meteorite strike on Mexico wiped out the dinosaurs is under sharp attack, again.
The asteroid that created the Chicxulub crater in the Yucatan peninsula in Mexico arrived too early to have caused the Cretaceous-Tertiary mass extinction, according to evidence given on 23 May at an American Geophysical Union conference in New Orleans, Louisiana.

A team led by palaeontologist Gerta Keller of Princeton University, New Jersey, reported that a sediment core drilled in east Texas emphatically confirms a study that the group released two years ago. Sediments of glass sprayed out by the Chicxulub impact are separated from fossils killed during the mass extinction by a 300,000-year gap, they argue.



"I believe this is the mortal wound for the Chicxulub theory." - Gerta Keller.
Scientists should mount a search for the crater left by the meteorite that was really responsible for the mass extinction, she adds.

Many geophysicists remain unswayed. Sean Gulick of the University of Texas at Austin doubts the report because it means another huge Asteroid must have hit the Earth in the same era, about 65 million years ago.
"The odds of that are highly unlikely," - Sean Gulick, who chaired the Chicxulub symposium at the conference.

However, some sedimentologists are being persuaded by the core specimens. Paul Wignall of the University of Leeds in Britain calls Keller's evidence "quite convincing", although he didn't attend the meeting.

Two years ago, Keller stunned a symposium at an American Geophysical Union meeting in Nice, France, with an analysis of a section of a 1,500-metre core drilled in the Yucatan, only 60 kilometres from the Chicxulub crater.

The Yucatan core, called Yaxcopoil-1, was the result of an international project designed to provide the most advanced record of events at the Cretaceous-Tertiary boundary. But it was beset by strife over access to the core and subsequent interpretations (http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v425/n6953/full/425013a_fs.html).

Keller claimed the crater preceded mass extinction by 300,000 years.
Her critics say the sediment layers she sees are actually rubble from collapsing crater walls. But her team argues that palaeomagnetic dating and minute fossil analysis rules this out.

To settle the dispute, Keller drilled 2,000 kilometres north of the crater to get a sedimentary view unaffected by backwash.

The Brazos River Valley, Texas, is widely accepted as the best location to check Chicxulub impact debris from afar. In March, three 50-metre-deep holes were drilled near the small town of Rosebud to extract sediment from the time of the mass extinction.

From a 2-metre section of the best core, the Keller team charted what they say shows the 300,000-year gap. First, there is a 2 centimetre-thick layer of altered glass called bentonite that is the ejected material from the Chicxulub impact. About 50 centimetres above that lie sediments beds from the tsunami set off by the asteroid.
Finally, a full 1.2 metres above these beds, there is the detritus of the mass extinction, represented by fossils of tiny plants and animals that died.

The National Science Foundation has given Keller US$40,000 to drill another core in autumn 2006. This one will be on the opposite side of the Chicxulub crater, some 7,800 kilometres south near the city of Recife in Brazil. Keller hopes to find evidence that will finally quiet her critics.

Extract:

Startling new evidence from boreholes drilled into the 120-mile-wide Chicxulub crater in Mexico indicate that the great impact, happened 300,000 years too early to have been the one that wiped out the dinosaurs.
The discovery comes at a time when some geologists are convinced that the Chicxulub event killed 70 percent of living species at the Cretaceous-Tertiary (K-T) boundary, 65 million years ago.
Several lines of geological evidence from Chicxulub make a compelling case for the crater having been formed too early to be the mass killer.
Evidence, broken `breccia` rocks, from a borehole, Yaxcopoil 1, was expected to provide final, irrefutable confirmation of Chicxulub's role in the K-T boundary mass extinction. It didn't.
On top of the impact breccia is about two feet of gently-laid-down, thinly layered seafloor mud built up over 300,000 years. Those two feet of post-impact mud have the fossils, carbon isotopes and magnetic signal of the late Cretaceous, before the mass die-off.
It's 300,000 years too early .
Also missing from the Yaxcopoil 1 borehole rocks is any significant iridium signal , the extraterrestrial element that first clued scientists into the fact that an asteroid might have caused the K-T extinctions.
As to what really caused the K-T mass extinction; it was probably another asteroid impact combined with intense volcanic activity., and, many dinosaur researchers suspect that dinosaurs were on the decline before the final mass extinction.
Chicxulub might have played a role in their extinction. but a second impact, still undiscovered, might have been the terminal blow.


Perhaps, a second impact (beneath the Indian Ocean?), 300,000 years after the Chicxulub collision, may have finished off the creatures...

The Chicxulub crater data was derived from analysed rock-core, using five separate indicators of age, including fossil planktonic organisms and patterns of reversals in the Earth's magnetic field.
It is supposed that the cooling of the global climate shortly followed by a period of greenhouse warming placed enormous stress on the dinosaurs.

Global warming could have been kicked off by carbon dioxide released by a massive eruption of lava that occurred at the same time, from the Deccan traps in India.

This Chicxulub impact occurred during a warming period and, although the environmental effects were severe, it is supposed did not directly cause the extinction of the dinosaurs.

Between 50 and 60 per cent of marine and terrestrial life forms became extinct during the KTB extinction, including the dinosaurs.
The cause of this mass extinction has received much attention from scientists over the last 25 years, since the detection of iridium-rich cosmic debris at the boundary layer around the world -- an element known to be rare on earth. This led to the theory that a meteorite impact could have been responsible for the debris and the mass extinction; the 180-km wide Chicxulub impact crater was eventually discovered in the Gulf of Mexico.
However, on the other side of the world, massive volcanic eruptions, known as the Deccan Traps continental flood basalt province, were simultaneously reaching their peak, forming a 2.5km thick pile of lava.
"Both the Chicxulub impact and the Deccan eruptions would have had the potential to induce detrimental environmental changes serious enough to significantly affect terrestrial ecosystems.
Dust-induced darkness, acid rain, wild fires and global warming would all have played a role in inducing biospheric trauma, but the timescales over which these were effective would be expected to be different, dependent on the event that caused them
.”
Charlotte used chemical and isotopic fingerprinting techniques on molecular fossils from North America, and more recently from New Zealand, to investigate patterns which would establish whether there was instantaneous change (as the result of a meteorite impact) or gradual change within the ecosystem (as caused by prolonged volcanism).
"Carbon isotopes can tell us a lot about the stability of an ecosystem and, together with the identification of molecular fossils, enables past variations in habitat, climate and biology to be investigated."
The aim of the project is to compare and contrast samples from several terrestrial and marine KTB successions, at varying palaeogeographical distances from the locations associated with the two putative causes of end-Cretaceous environmental stress. In effect the project examines the effects of these two environmental disasters working outwards from the 'ground zero' locations.
Results taken from samples in the Western Interior of North America show that the ecosystem experienced a short sharp shock at the boundary consistent with a meteorite impact. Early analysis of the New Zealand samples also point to a meteorite impact.


Go to The Chicxulub Debate website



-- Edited by Blobrana at 23:26, 2005-05-24

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The catastrophe that wiped out the dinosaurs and many other species 65 million years ago has been clarified.
The meteorite that caused their deaths left its largest evidence in Cuba.



Today it seems to be definitely accepted, said Dr. Manuel Iturralde to Sol y Son. Dr. Iturralde, a specialist with Cuba`s National Museum of Natural History, explained that the massive extinction 65 millions years ago in which dinosaurs disappeared was caused by the meteorite of Chixculub, Mexico.
The hypothesis of the `killer meteorite` emerged in 1979 when physicists Harold Urey and Luis `lvarez found abnormal concentrations of iridium in sediments from the late Cretaceous period Iridium is rare on Earth, but there is plenty of it in asteroids and it is thought that the impact of one with a diameter of over six miles induced earthquakes, volcanic eruptions and a `nuclear winter` with a sudden drop in temperature.

Such an impact would make a crater with a 240 km diameter. Since none like that was found on land, they looked for it at sea.
In 1990, Bohor and Seitz, two US geophysicists, discovered that 650 thousand centuries ago a giant meteorite fell in Chixculub, in the Yucatan peninsula, Mexico, near the south-western coast of Cuba.
The evidence should be in the geological strata of the late Cretaceous or early Tertiary periods, (K-T layer, according to experts), for its lower part contains fossils of the disappeared animals, which were not present in the upper part.
Also there should be quartz particles crushed by the impact, as well as microtectites, or crystal balls formed when the molten rock solidifies, usually found around meteor craters. And, of course, iridium.

Cuban Evidence

Iturralde`s attention was caught by a paper published in Nature magazine. "I went to the Cuban areas where allegedly were fragments of the impact, but the rocks there were not originated by a meteor. Two years later I published a paper on the subject in Earth and Planetary Science and Letters."
In 1996 Dr. Takafumi Matsui, from the University of Tokyo, visited Cuba with a project on the Tertiary geological limit and signed a collaboration agreement with the Museum of Natural History and the Institute of Geology and Paleontology.
During the past five years several expeditions studied the K-T layer in the provinces of Pinar del Ruo, Havana, Matanzas and Villa Clara.

Unique cuts were found, for if the deposits in Mexico and other countries of the area are 6 to 10 feet deep, in Cuba they go down to almost three thousand.

"They are unique, and indicate the most complete vestiges of the impact and its consequences." - Dr. Manuel Iturralde

What produced such unusual thickness? When the meteorite fell in Yucatan, what was then the bottom of the Caribbean and the edge of the peninsula is now what is found in Pinar del Ruo, Havana and Matanzas.
That is, Cuba has rocks that were part of the bottom of the Caribbean Sea and the Yucatan shores.

An Extraterrestrial Earthquake

According to Iturralde the impact generated a shock wave with an earthquake way beyond any of terrestrial origin, so great that it provoked an enormous crumbling of the continental edge in Yucatan, the Bahamas platform and the then existing islands, which at present are the foundation of Cuba. The crumbling made deposits hundreds of feet thick, gaps with enormous blocks torn from the near emerging areas.

"Gigantic tsunamis crashed on the Caribbean coasts rolling over small islands and low areas, with billions of tons of dust and sand. When they settled, that material when to the bottom of the sea and created the huge layers that we have found" Dr. Manuel Iturralde.

The impact pulverized the meteorite, rocks were fused and flew to the atmosphere, which received that iridium-rich dust, crystals generated by the fusion and cooling of the rock, and also laminar quartz. Due to the impact, all that is on Cuban rocks

Prehistoric Nuclear Winter

"Most probably all sea organisms in the Caribbean did not survive. Not only dinosaurs were extinguished" - Dr. Manuel Iturralde.
At the International Congress of Geology held in Havana, Dr. Ryuji Tada, a researcher from the University of Tokyo, said that science links the impact with a world environment crisis - acid rains, fragments falling from the sky and cooling for a long period, because the particles in the atmosphere blocked solar radiation, a kind of `prehistoric nuclear winter.`

This brought massive deaths that in turn generated plagues, bacteria, fungi and diseases for wildlife and flora, which in turn contributed to the death of more species. The destruction of plants and forests left them without food, the massive fallout and acid rains generated chemical changes in the composition of the water in the seas, rivers and lakes.

Many species survived, but also many were totally extinguished, like dinosaurs. At present there is a second project with universities from Spain and Mexico, led by Reinaldo Rojas, the Museum`s director, which will study marine life before and after the impact, something that was not done during the previous research.

"People sometimes wonder. why so much money is spent on studying the past when there are so many problems today, but those studies allow us to better know the whys of the present and prepares us for the future. What happened in the past on Earth could happen again, and all that history is in the rocks, so if we study them we`ll know what happened, what could happen and how to find ways to be prepared for tomorrow." - Dr. Manuel Iturralde.

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Blobrana wrote:




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...

As to what really caused the K-T mass extinction; it was probably another asteroid impact combined with intense volcanic activity., and, many dinosaur researchers suspect that dinosaurs were on the decline before the final mass extinction.
Chicxulub might have played a role in their extinction. But a second impact, still undiscovered, might have been the terminal blow.


...

Keller plans to bolster her case with an upcoming paper that argues that meteorite impacts that leave Chicxulub-size craters and smaller cannot by themselves cause significant species extinctions. The amount of material ejected, she finds, is insufficient to trigger long- lasting climatic or geographic changes from fire or floods. Sudden mass extinctions might require the coincidence of major volcanism and a large impact event, "but so far no one has found the source crater," Keller says in her dismissal of Chicxulub.

...



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That's what I thought every time I heard claims that the Chicxulub was responsible for the extinction of the dinos.

I'm just putting together an web page. On this page you will find an map, showing North Pole, Skandinavia, Europe and North Africa in a 3d style - and also the floor of the mediterranian see and the atlantic ocean.

My attention was attracted by 4-5 locations on this map that reminded me strongly of huge impact craters. If they really are what I suspect (and if they were formed in the proper period of time, of course), they might possibly have been *ALL TOGETHER* the reason why the dinos were weeped out...

But in a few weeks time you should be able to judge the map yourself - I also plan to send a link to my page (once it is online) to Prof. Dr. Keller and Dr. W. Stinnesbeck.

I just received the permission to publish the map on my page - so I can go ahead with it now.

It`s just that I will be quite busy during the next time (on vacancy and after that heavily expanding my good old A4kCSPPC with Mediator and all the PCI stuff) and so it might take a while...


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Scientists have found rare fossils that are shedding new light on what wiped out the dinosaurs at the end of the Cretaceous period 65 million years ago.
For more than a decade, the standard view has envisioned a speeding object from space that crashed into the earth and kicked up enough dust and rock around the globe to blot out the sun. The smoking gun seemed to be the discovery beneath the Yucatán peninsula of Mexico of a 110-mile-wide crater called Chicxulub, after a nearby town.

But lately, doubters have argued that Chicxulub formed 300,000 years before the mass extinction - too early to have played a role in the demise of the dinosaurs and hundreds of other plant and animal species that vanished at the end of the Cretaceous.
The team of scientists zeroed in on Cuba as an ideal place to seek clues, having heard from Cuban colleagues of a possible trove of fossils of the right age. The Cuban zone was 600 miles from the Mexican crater.
Now, in the September issue of Geology, the scientists, from Spain, Cuba and Mexico, report that they have discovered a highly disturbed bed of fossils that bears numerous signatures of Chicxulub's mayhem. The date of the disturbance, 65 million years ago, is exactly at the end of the Cretaceous.


Courtesy of Dr. Laia Alegret

"The site is located opposite a military base. So it's almost impossible to get a work permit" - Laia Alegret, a team geologist at the University of Zaragoza in Spain.

The discovery was outside Santa Clara, a city in central Cuba whose nearby air base drew scrutiny in 1962 when American spy planes spotted Soviet jets and antiaircraft missiles.

"It was definitely a hot spot" - Timothy Naftali, a cold war historian at the University of Virginia.

Starting around 2000, Dr. Alegret and her European colleagues repeatedly sought work permits for a nearby hill but always met with stultifying delays, if not outright rejections. Finally, they slipped into the site with their Cuban colleagues, going in late 2000, 2002 and 2003. At other times, the Cubans went in alone.
A rocky outcrop on the hill showed an exposed bed of sedimentary rock made up of broken bits of minerals and fossils. It was more than 30 feet thick. The team took 66 samples. Examination with microscopes showed quartz deformed by high temperatures and pressures, as well as tiny spheres of glass, both clearly debris from a spectacular fireball.

Microscopic study also revealed the presence of thousands of tiny fossil creatures, most especially foraminifera. Those one-celled animals have a bewildering array of minuscule shells. Forams, as they are known, evolve so fast that geologists, palaeontologists and oil companies use their shifting appearance as reliable guides to geologic dating.

"They told the age of the sediments. So we've definitely confirmed the age of these deposits" - Laia Alegret.

At the end of the Cretaceous, the rocky bed now in Cuba formed on the ocean bottom at a depth of perhaps 3,300 feet, over a few days or weeks as tons of debris rained down from the sky and huge waves generated by the Chicxulub event washed land out to sea.

"It was geologically instantaneous" - Dr. Laia Alegret.

Earth movements over the ages turned that part of the seabed into land.
Dr. Alegret's co-authors include Ignacio Arenillas, José A. Arz, Alfonso Meléndez, Eustoquio Molina and Ana R. Soria of the University of Zaragoza; Consuelo Díaz of the Institute of Geology and Paleontology in Havana; José M. Grajales-Nishimura of the Mexican Institute of Petroleum in Mexico City; and Reinaldo Rojas of the National Museum of Natural History in Havana.
Dr. Alegret said that because of the site's importance, her Cuban colleagues were talking with the government to have it protected from rain and erosion. The aim is to save the outcrop for scientific study.

Adapted from source


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Cuban Scientists Study Meteorite Fragments

SANCTI SPIRITUS, Cuba- Cuban experts have inspected a site near the town of Fomento in Sancti Spiritus province, and found clues of the impact of an enormous meteorite with the Earth during the Cretaceous period (about 65 million years ago).

Reinaldo Rojas, head of the Limite KT project in Cuba, which is in charge of the exploration said that the site shows abundant material to be taken as the main point for the research.
Rojas explained that after digging three meters into the rocky surface, scientists discovered meteoritic glass, small quartz grains, and sediments, as well as a fossil macrofauna and microfauna, all proofs of a collision.
The scientist estimates that 65 million years ago, the town of Fomento in central Cuba was located about 500 Km from the meteorite-hit place in the Mexican Yucatan Peninsula; thereby, what it’s been recently detected should have been thrust by the meteorite’s powerful energy waves when it struck Yucatan.
Its crash with the Earth unleashed high temperatures and pressures, as well as great volumes of gases identical to those of a colossal atomic explosion causing one of the largest life extinctions on the planet, he explained.
Prior to this ongoing study, Cuban specialists had only records of the fallen meteoroid in rocks of western Cuban provinces from Pinar del Rio to Matanzas, and in La Loma del Capiro in Sancta Clara city.

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Cuban researchers say there are signs in the centre of Cuba of the Chicxulub meteor.
Fossilised remains of oysters and sea urchins have been identified at a late-Cretaceous dig site in the central Cuban province of Sancti Spiritus.

`The fossils "shared with the dinosaurs the colossal catastrophe" and represent part of an "animal guide to the late Cretaceous" period` - Abel Hernandez, ecologist and one of a team of researchers working at the site.

The Chicxulub impact released a force of five billion atomic bombs, and let loose huge clouds of sulphuric acid and particulate matter that blocked the sun's rays and caused mass extinction of animal and plant species, opening the way to a new geologic era.

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Cretaceous
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China has begun to drill the first well as part of scientific research on climate change that occurred during the Cretaceous period, in Daqing city of Heilongjiang province in northeast China.

Professor Wang Chengshan from China's University of Geosciences, the lead scientist in the project, said that the research will be aimed at probing climate change during a period from 65 million to 140 million years ago.
Meanwhile, he said the drilling would also help to probe the oil reserve for the sustainable development of the Daqing oil field.

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Growing evidence shows that the dinosaurs and their contemporaries were not wiped out by the famed Chicxulub meteor impact alone, according to a palaeontologist who says multiple meteor impacts, massive volcanism in India and climate changes culminated in the end of the Cretaceous Period.

The Chicxulub impact may have been the lesser and earlier of a series of meteor impacts and volcanic eruptions that pounded life on Earth for more than 500,000 years, say Princeton University palaeontologist Gerta Keller and her collaborators Thierry Adatte from the University of Neuchatel, Switzerland, and Zsolt Berner and Doris Stueben from Karlsruhe University in Germany.
A final, much larger and still unidentified impact 65.5 million years ago appears to have been the last straw, said Keller, exterminating two-thirds of all species in one of the largest mass extinction events in the history of life. It's that impact - not Chicxulub - that left the famous extraterrestrial iridium layer found in rocks worldwide that marks the impact that finally ended the Age of Reptiles, Keller believes.

"The Chicxulub impact alone could not have caused the mass extinction, because this impact predates the mass extinction" - Gerta Keller.

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There's growing evidence that the dinosaurs and most their contemporaries were not wiped out by the famed Chicxulub meteor impact, according to a palaeontologist who says multiple meteor impacts, massive volcanism in India, and climate changes culminated in the end of the Cretaceous Period.
The Chicxulub impact may, in fact, have been the lesser and earlier of a series of meteors and volcanic eruptions that pounded life on Earth for more than 500,000 years

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