The rise of mammals may have been caused by the high-speed impact from a comet around 55 million years ago, according to a new study published in the journal Science.
The study actually provides new evidence of an existing and controversial theory; a comet impact caused an era of rapid global warming that allowed for the rise of modern mammals.
Around 55.6 million years ago, the amount of atmospheric carbon dioxide rose significantly. The ensuring period of global warming, known as the Palaeocene-Eocene Thermal Maximum (PETM), is thought to have allowed mammals to populate new areas of the Earth, particularly areas closer to the poles.
The new study is based on an analysis of spherical bits of glass found in sediment cores drilled off the coast of New Jersey. The round pieces of glass are believed to form when liquid debris flung out by a high-energy impact solidifies in mid-air.
These bits of ancient glass were flung outward during the comet’s impact. (Credit: Megan Fung)
The study team was particularly interested in a mineral found in the bits of glass called lechatelierite. The inclusion of this mineral is difficult to explain without a highly dynamic event like a comet impact. Volcanic activity has been cited by some scientists cited as the cause for the PETM, but magma does not reach the temperatures needed to form lechatelierite.
Using ‘Shocked Quartz’ to Study the Past
Another line of evidence arises from the discovery of grains of shocked quartz within one of the spherules. These “shocked grains” happen when quartz is bumped out of shape under the type of extreme strain generated by an extreme collision. The pressure in a volcano isn’t enough to generate these grains.
Christian Koeberl, a University of Vienna scientist who was not involved with the study, told BBC News that the use of that Raman spectrometry to identify shocked quartz was a curious choice.
“This is not a standard method to identify shocked quartz, so maybe it is, maybe not,” he said.
Koeberl added that there are also still major doubts about the age of the glass spherules in the study.
“The information given so far is not conclusive on this point – it is not impossible that the spherules are derived from another stratigraphic layer (I hope contamination can be excluded, which is not uncommon either – spherules have been found in many strange locations). So age dating would be helpful,” he said.
Image credit: Thinkstock
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