Did gamma rays from outer space kill off the dinosaurs?
Fans of dinosaur models and fossil collectors have a chance to peruse a new research paper, in which a team of US scientists has disproved the theory that intense radiation killed off the dinosaurs. Research by 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.
The mass extinction event sixty-five million years ago wiped out approximately seventy percent of all terrestrial life on Earth. The dinosaurs went extinct along with several families of marine invertebrates, types of plants, marine reptiles, and the pterosaurs.
Although many paleontologists accept that the Earth was hit by a giant extraterrestrial object that led to the end of the Mesozoic, a theory first put forward by physicist Luis Álvarez and his son (a geologist) in 1980 and largely corroborated with the discovery ten years after the Chicxulub impact crater. Debate continues among the scientific community about the evidence for an asteroid impact that actually led to the mass extinction. Other theories of extinction have been postulated, many of them linked to other dangers in outer space. The intense activity of solar flares from the sun could have affected Earth’s climate and bombarded the planet with harmful rays. A supernova explosion could have caused a dramatic increase in gamma radiation, which if it had occurred would have had devastating consequences for life on Earth.
The Earth subject to Cosmic Rays
If the Earth had been exposed 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 radiation-induced cancers. Evidence of strong doses of radiation in prehistory is difficult to identify, but cancers and other abnormalities caused by increased radiation could be detected in the fossil record. Dr. Adrian Melott, assisted by his colleague Bruce Rothschild, carried out a study of 708 fossilized dinosaur bones from late Maastrichtian sediments (70-65 million years ago) to see if they could find evidence of an increase in bone cancers among the last dinosaurs.
When they compared the incidence of bone cancer with close living relatives of dinosaurs (birds and reptiles), the team found no evidence of elevated cancer rates in dinosaurs.
However, Dr. Melott will keep looking, his work continues. The results for hadrosaurs (duck-billed dinosaurs like Edmontosaurus and Anatotitan), which lived during the last five million years of the reign of the dinosaurs, are intriguing. Hadrosaurs had the only case of bone cancer and the only cases of benign abnormalities called hemangiomas.
Looking for fossil evidence
Hemangiomas are an abnormal buildup of blood vessels in the skin or internal organs, sometimes called “strawberry marks.” They are frequently found in Caucasian races and are more common in women. Evidence from hadrosaur bones shows signs of hemangiomas, could this be cosmic ray evidence or are the results of this early study not statistically valid? Perhaps the migratory lifestyle of these animals made them more susceptible to such conditions, or it could simply be that there are so many more hadrosaur fossils to study that bone cancer and other anomalies were virtually guaranteed to be found in this group, since they represent such a large part of the Late Cretaceous fossil record.
Scientists are still not sure about the exact causes of the mass extinction event, fans of dinosaur models often build prehistoric scenes with dinosaurs that lived at the end of the Cretaceous: Triceratops, T. rex and Ankylosaurus.
