No Evidence to suggest that Gamma Rays led to Mass Extinction
Research from astrobiologists at the University of Kansas has concluded that bursts of intense gamma radiation or other cosmic rays are unlikely to have led to the mass extinction event at the end of the Cretaceous.
Although, many palaeontologists accept that the Earth was hit by a giant extra terrestrial object 65 mya, a theory first put forward by physicist Luis Alvarez and his son (a geologist) in 1980 and corroborated to a considerable extent with the discovery ten years later of the Chicxulub impact crater. Debate still rages amongst the scientific community over the evidence of an asteroid impact actually leading to the mass extinction. A number of other extinction theories have been postulated, many of them linked to other dangers in outer space. Intense solar flare activity from the sun could have affected the Earth’s climate and bombarded the planet with harmful rays. The explosion of a super-nova could have led to a dramatic increase in gamma radiation, these if they did happen, would have had devastating consequences for life on Earth.
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If the Earth had been subjected to intense cosmic rays, this would have had a number of serious consequences for life, food chains would have collapsed and animals would have suffered from birth deformities, sterility, mutations and cancers caused by the radiation. Evidence of heavy doses of radiation in pre-history is difficult to identify but cancers and other abnormalities caused by the increased radiation could be detected in the fossil record. Dr Adrian Melott assisted by his colleague Bruce Rothschild carried out a study of 708 fossilised dinosaur bones from late Maastrichtian stage sediments (70-65 mya) to see if they could find evidence of increased bone cancers amongst the last dinosaurs.
When they compared the incidence of bone cancer with living, close relatives of dinosaurs (birds and reptiles), the team found no evidence for elevated cancer rates in dinosaurs.
However, Dr Melott is going to keep looking, his work is on-going. The results for Hadrosaurs (duck-billed dinosaurs such as Edmontosaurus and Anatotitan, which lived during the final 5 million years of the dinosaurs’ reign, are intriguing. Hadrosaurs had the only case of bone cancer and the only cases of benign abnormalities called haemangiomas.
Haemangiomas are an abnormal build up of blood vessels on the skin or internal organs – sometimes called “strawberry marks”, they are found frequently in Caucasian races and are more prevalent amongst females. Evidence from Hadrosaur bones show signs of haemangiomas, could this be evidence of cosmic rays or are the results of this initial stud not statistically valid. Perhaps the migratory lifestyle of these animals made them more susceptible to such conditions, or could it simple be that there are so much more Hadrosaur fossils to study that it was practically guaranteed to find bone cancer and other abnormalities in this group as they represent such a large proportion of the Late Cretaceous fossil record.