Nickel isotopes preserved in the global clay layer left by the Chicxulub impact point to a rare CO carbonaceous chondrite as the likely dinosaur-killing object without identifying its precise source, leaving the classification a geochemical inference from minute traces. [1]

Researchers analyzed samples from the clay deposited after the impact 66 million years ago, when the original projectile vaporized and left only a small fraction of its material in the layer, and ScienceDaily, carrying edited University of British Columbia material, says the isotope signature narrowed the object to the Ornans class of carbonaceous chondrites. [1]

That class is uncommon and contains less sulfur and other volatile material than several other meteorite classes, so the researchers argue that sulfur carried inside the impactor was less likely to be the principal cause of the climate disaster and fine debris thrown into the atmosphere may have mattered more, while sulfur from the rock struck on Earth and other extinction processes remain part of the question. [1]

The source orbit is also unresolved, as the object may have come from the outer asteroid belt near Jupiter or another distant region of the solar system, while isotope uncertainty, contamination, sample selection and comparison with related carbonaceous classes still require scrutiny and replication.

ScienceDaily's headline says scientists identified the rare meteorite, but the study has instead reduced a field of possibilities to a likely class, a sharper account of the impactor's composition rather than a recovered name tag or a single completed explanation for the extinction.

-- PRIYA SHARMA, Delhi