By Sid Perkins
Scientists sifting through ancient sediments laid down just after Earth’s most devastating episode of extinctions may have found minuscule fragments of the massive extraterrestrial object suspected to have caused the catastrophe.
About 250 million years ago, at the end of the Permian period, 95 percent of the species in the oceans and 70 percent of those on land went extinct (SN: 2/1/97, p. 74). That makes the famous mass extinction that wiped out the dinosaurs some 65 million years ago seem like a minor die-off. Previous chemical analyses of some gases and other matter in sediments deposited during the transition between the Permian and Triassic periods suggest that these materials came from outer space (SN: 2/24/01, p. 116: Extinctions Tied to Impact from Space). Now, researchers examining the same sediments have extracted microscopic fragments of metals and minerals that also bear an extraterrestrial fingerprint.
The samples that scientists analyzed were excavated from a 25-centimeter-thick, clay-rich layer at Antarctica’s Graphite Peak, says Asish R. Basu, a geochemist at the University of Rochester in New York. Researchers used magnets and ultrasound to extract dozens of magnetic particles from the powdery material.
Many of the particles contain iron- and nickel-rich oxide and sulfide minerals, as well as small grains of silicates, says Basu. The chemical composition of the grains in these mixed-mineral particles–including their low concentration of iron oxide and high ratio of manganese to iron–strongly suggests that the minerals didn’t crystallize on Earth. Such a chemical mix is found only in a type of meteorite that formed about 4.5 billion years ago, soon after our solar system began to coalesce, Basu notes. He and his colleagues report their research in the Nov. 21 Science.
The team’s findings could be additional evidence that the impact of an extraterrestrial object caused the Permian extinctions, says Michael R. Rampino of New York University.
The magnetic fragments that Basu and his team found “clearly are little pieces of meteorite,” Rampino says, but he cautions that they could be part of the normal flux of micrometeorites that fall to Earth. Basu counters that similar fragments don’t show up in the coal bed that lies just below the clay-rich stratum, so the bits of ancient meteorite aren’t part of that everyday accumulation.
Bits of iron similar in size and shape to those found in Antarctica have turned up elsewhere in sediments that mark the end of the Permian period, including some formerly deep-sea accumulations now found on land in Japan and in some Chinese deposits that had accrued in shallow water. Rampino suggests that regardless of the source of the Antarctic fragments, their fall to Earth 250 million years ago was part of a worldwide phenomenon that may or may not have been cataclysmic.
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