New Studies Point Finger at Deccan  Traps for Demise of the Dinosaurs

In 1980, American scientists Luis and Walter Alvarez published their theory regarding an extra-terrestrial body impacting with the Earth, causing the mass extinction event that marked the end of the Age of Reptiles.  The discovery of the Chicxulub crater in the Gulf of Mexico, the “smoking gun” evidence in the 1990’s added credence to this theory put forward by the father and son team.

Recent studies of the asteroid belt that lies between Mars and the outer planets had led one group of scientists to deduce the fate of the dinosaurs was sealed back in the Jurassic when an impact between huge asteroids sent one immense lump of space rock on a collision course with Earth:

Article here: Dinosaur extinction set in motion by asteroid collision in the Jurassic

Now a second team of American scientists have challenged the asteroid/meteorite theory and proposed that massive volcanic eruptions in India led to the demise of the Dinosaurs and about 65% of all life on Earth.  New studies of the enormous basaltic lava flows of western and central India – known as the Deccan Traps, indicate that the most violent and devastating eruptions are dated very closely to the mass extinction event.

Volcanic activity on this scale would have thrown out into the atmosphere huge volumes of carbon dioxide and sulphur dioxide, dramatically changing the world’s climate and leading to the collapse of entire ecosystems.

The Deccan Traps is one of the largest volcanic provinces on the planet.  The basaltic lava flows that occurred around 70-65 million years ago, cover an area of over 500,000 square kilometres, this is twice the size of the whole of the United Kingdom.  In parts, the basalt is over 2 kilometres deep.  Plate movements and other tectonic factors have broken up the lava deposits, some scientist estimate that the volcanic activity at the end of the Cretaceous deposited enough lava to cover 1,500,000 square kilometres – this would have covered half of India.

Map Showing the Extent of the Deccan Traps

Picture credit: BBC

It has been accepted for some time that these enormous eruptions would have had a devastating effect on the Earth’s climate.  Apart from the damage caused by the eruptions themselves, the smoke and the ash clouds would have been vast and disrupted the climate.  The sulphur dioxide pumped into the air would have led to acid rain and the carbon dioxide and other gases, as well as being toxic to life would have led to global warming.  This new study by the American team dates the most massive volcanic activity right up against the K-T boundary and as a result the research team has published a paper claiming that it was these eruptions and not the asteroid impact that led to the wipe-out.

The main period of eruptions has been linked chronologically to the estimated date for the beginning of the extinction phase, during this period geologists estimate that ten times more climate changing gases would have been released compared to the Chicxulub impact event.  So it was probably the volcanic activity that did for the Earth’s climate, although the huge extraterrestrial impact could not have come at a worse time and would have added to the environmental chaos.  As indeed with other impacts (some scientists believe there were two such impacts, only 300,000 years apart, in geological time very close to each other – a real double whammy.

Previous dating techniques involved paleomagnetic signatures of crystals formed in the lava as it cooled.  These indicated that the main eruptions occurred around 800,000 years before the geological boundary between the Mesozoic ending and the Cenozoic beginning.  More recent studies measuring the radioactive decay of argon and potassium isotopes in the lava deposits placed the biggest period of volcanic activity within 300,000 years of the K-T boundary.  However, it is evidence from tiny marine micro-fossils that the American researchers believe prove the volcanic activity to be a direct cause of the mass extinction.

Scientists are confident that shortly after the mass extinction event, one of the first signs of ecosystems beginning to recover was the establishment of new types of planktonic foraminifera (similar to the animals that helped form the white cliffs of Dover).  Analysis of deposits in Bay of Bengal region of the Deccan traps has shown that marine sediments were deposited on top of the basaltic lava from the most active phase of the Trap’s formation.  In these marine deposits, evidence of the foraminifera micro-fossils have been found, indicating that these marine deposits were laid down almost immediately after the extinction event.  It is therefore logical to deduce that the lava deposits immediately preceding the marine sediments must have been laid down about the time of the death of the dinosaurs and the wiping out of much of life.

The American team’s paper has already received support from a number of notable academics from Europe.  It was formerly presented at the annual meeting of the Geological Society of Denver has received widespread comments and reviews.  The sheer magnitude of the volcanic activity certainly played a role in climate change but this study of the micro-fossils puts the worst of the eruptions immediately prior to the mass extinction, as if these eruptions triggered the extinction event.

The American team has cited a number of other studies which support their conclusions and state that their work sheds light on an anomaly that the Chicxulub impact theory supporters have not been able to resolve.  Analysis of other sites around the world along the K-T boundary and from sediments laid down thousands of years after the extraterrestrial impact show that life on Earth was very slow to recover.  The micro-fossils do not enter the fossil record for another 300,000 years post the asteroid/meteorite collision.  The fact that the marine environment does not show any signs of recovery for about 300,000 years after the impact, can be explained by looking at the lava deposits above the tell-tale marine deposits in the Bay of Bengal.  These younger deposits of lava were laid down after the mass extinction event, but still caused enough disruption to delay the recovery of life on Earth.  According to the American researchers the last period of Deccan Trap eruptions occurred in the early Palaeocene (Danian faunal stage) about 280,000 years after the end of the Mesozoic.  It was these eruptions that caused the delay in the recovery of life forms and the building up of ecosystems.

The fossil record indicates that there have been a number of mass extinction events in the history of life on Earth.  It is certain that the K-T boundary represents a period of dramatic environmental change.  The dual effect of the formation of the Deccan Traps coupled with asteroid impacts would explain the mass extinction, the dying out of the non-avian dinosaurs, marine reptiles, pterosaurs, certain birds, ancient crocodiles, and many kinds of invertebrates could be due to a number of factors.  This is not doubted, what remains in dispute is the contribution to the mass extinction each of these factors played.

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