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- Ελληνικά
It was spring and flowers were blooming when the end of the dinosaur age came. That is the romantic yet sad conclusion of a new European scientific study, which for the first time makes an estimate of the specific time of year when, some 66 million years ago, the great asteroid that led to the extinction of almost all of the planet's hitherto dominant species fell on Earth.
Researchers from Sweden, France, the Netherlands, Belgium and Britain, led by Dr Melanie Durring of Sweden's Uppsala University, who published the paper in the journal Nature, estimate that the impact of asteroid Chicxulub in the region of the Yucatan Peninsula of present-day Mexico occurred when it was spring in the northern hemisphere. The cataclysmic event is estimated to have brought about a mass extinction of species, about 76% or three quarters of all that lived on Earth. Among the victims were the non-flying dinosaurs, pterosaurs, ammonites and most marine reptiles, while mammals (which now paved the way for subsequent dominance), birds, crocodiles and turtles survived.
To date, determination of the impact had focused on the timing of the event with deviations on the order of a few thousand years, but the time of year was unknown. The researchers first studied the remains of fish that had died en masse on that day and were found in North Dakota, USA, using high-resolution X-ray tomography at the European Synchrotron Radiation Facility (ESRF) accelerator to analyse the growth patterns imprinted on their fossil bones. Combined with the analysis of evidence of carbon isotopes in the fish bones, the "verdict" was that the disaster came in the spring.
Huge waves in seas, lakes and rivers
Among other things, the impact of the large meteorite caused huge waves in seas, lakes and rivers, burying many fish alive. The fish had fragments from the impact in their gills, but not lower in their digestive tract, indicating that their deaths were almost instantaneous and occurred less than an hour after the impact.
The spring asteroid fall, if confirmed, would have coincided with a particularly sensitive stage for many species that were reproducing and growing at that time of year, which would have contributed to their subsequent mass extinction. On the other hand, species in the southern hemisphere, where autumn would have been present at the time, appear to have subsequently recovered at twice the speed of those in the northern hemisphere, according to the researchers.
Source: APE-MPA
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