Planetary securityStudy: dinosaurs killed off by more than one asteroid impact
The scientific consensus about the extinction of the dinosaurs 65 million years ago — along with more than half of other species then alive on Earth — is that an asteroid hit at Chicxulub in the Gulf of Mexico, creating a crater more than 180 km across and sending tons of smoke and soot into the atmosphere; scientists now say that the Chicxulub impact began the process of killing off the dinosaurs, but that the coup de grace occurred two to five thousand years later, with an asteroid impact in the Boltysh crater in the Ukraine
Asteroid impacts have happened before // Source: bbc.co.uk
Dinosaurs, along with more than half of other species, became extinct at the end of the Cretaceous period about 65.5 million years ago, and many scientists believe this was due to a single impact with an asteroid that hit at Chicxulub in the Gulf of Mexico. Now a study published in the Geology journal proposes the impact that produced the Boltysh crater in the Ukraine may also have been involved in the extinctions, and there may have been a shower of asteroids or comets.
Professor David Jolley of Aberdeen University in Scotland and Professor Simon Kelley of the Open University led a team studying the Boltysh crater, which was discovered in 2002. The Boltysh crater is only twenty-four kilometers in diameter and therefore much smaller than the Chicxulub at more than 180 km across.
The team studied fossilized plant pollen and spores found in the mud that filled the Boltysh crater, and found that ferns colonized the area soon after the impact, but there was another colonization a meter above the first, suggesting a second asteroid impact had occurred elsewhere causing repeat devastation. The researchers attributed this second spike, which occurred two to five thousand years later, to the aftermath of the Chicxulub impact.
Ferns are known to colonize devastated areas rapidly after disasters, so layers of fern spores known as “fern spikes” are considered to be good indicators of impact events in the past.
Other theories for the mass extinctions include enormous volcanic eruptions of the Deccan Traps in India about the same period that would have spewed toxic gases into the atmosphere. There is also a theory the asteroid impact triggered global earthquakes that in turn caused the Deccan Traps eruptions.
Professor Kelley said it is possible evidence will be found in future for more impact events around the same time, suggesting dinosaurs and many other species may have been wiped out due to the effects of an asteroid shower lasting thousands of years.
—Read more in David Jolley et al., “Two large meteorite impacts at the Cretaceous-Paleogene boundary,” Geology 38 no. 9 (30 April 2010): 835-8 (doi:10.1130/G31034.1)
