The space rock that hit Earth 65m years ago and is widely implicated in the end of the dinosaurs was probably a speeding comet, US scientists say.
Researchers in New Hampshire suggest the 180km-wide Chicxulub crater in Mexico was carved out by a smaller object than previously thought.
Many scientists consider a large and relatively slow moving asteroid to have been the likely culprit.
Details were outlined at the 44th Lunar and Planetary Science Conference.
But other researchers were more cautious about the results.
“The overall aim of our project is to better characterise the impactor that produced the crater in the Yucatan peninsula [in Mexico],” Jason Moore, from Dartmouth College in New Hampshire, told BBC News.
The space rock gave rise to a global layer of sediments enriched in the chemical element iridium, in concentrations much higher than naturally occurs; it must have come from outer space.
However, in the first part of their work, the team suggests that frequently quoted iridium values are incorrect. Using a comparison with another extraterrestrial element deposited in the impact – osmium – they were able to deduce that the collision deposited less debris than has previously been supposed …..
…. Read more at: http://www.bbc.co.uk/news/science-environment-21709229
Zircon U-Pb Geochronology Links the End-Triassic Extinction with the Central Atlantic Magmatic Province
Terrence J. Blackburn et al
The end-Triassic extinction is characterized by major losses in both terrestrial and marine diversity, setting the stage for dinosaurs to dominate Earth for the next 136 million years. Despite the approximate coincidence between this extinction and flood basalt volcanism, existing geochronologic dates have insufficient resolution to confirm eruptive rates required to induce major climate perturbations. Here, we present new zircon U-Pb geochronologic constraints on the age and duration of flood basalt volcanism within the Central Atlantic Magmatic Province. This chronology demonstrates synchroneity between the earliest volcanism and extinction, tests and corroborates the existing astrochronologic time scale, and shows that the release of magma and associated atmospheric flux occurred in four pulses over ~600,000 years, indicating expansive volcanism even as the biologic recovery was under way….