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Sioux Falls Scientists endorse Extinction for exploring how and why 95%
of life went extinct 250 million years ago in the greatest mass extinction.

Extinction
How Life on Earth Nearly Ended 250 Million Years Ago
By Douglas H. Erwin

Extinction (2006) - 296 pages
Extinction at Amazon.com

Some 250 Million Years Ago, the Earth suffered the greatest biological crisis in its history. Around 95 percent of all living species died out - a global catastrophe far greater than the dinosaurs' demise 65 million years ago. How this happened remains a mystery. But there are many competing theories. Some blame huge volcanic eruptions that covered an area as large as the continental United States; others argue for sudden changes in ocean levels and chemistry, including burps of methane gas; and still others cite the impact of an extraterrestrial object as responsible, similar to what caused the dinosaurs' extinction.

Extinction is a paleontological mystery story. Here, the world's foremost authority on the subject provides a fascinating overview of the evidence for and against a whole host of hypotheses concerning this cataclysmic event that unfolded at the end of the Permian.

Erwin begins by setting the scene, taking us from the 250-million-year-old early Triassic rocks of the dry mesas of Utah - where the fossils, few and far between, are almost identical to those of the same age in northern Italy, Iran, and China - to the richly abundant 265-million-year-old Permian fossils of the Guadalupe Mountains of Texas. After introducing the suite of possible perpetrators and the types of evidence paleontologists seek, he unveils the actual evidence - moving from China, where much of the best evidence is found; to look at extinction in the oceans; to the extraordinary fossil animals of the Karoo Desert of South Africa. Erwin reviews the evidence for each of the hypotheses before presenting his own view of what happened.

Although full recovery took tens of millions of years, this most massive of mass extinctions was a powerful creative force, setting the stage for the development of life as we know it today.

Douglas H. Erwin is Senior Scientist and Curator in the Department of Paleobiology at the Smithsonian's National Museum of Natural History and an External Faculty member of the Santa Fe Institute. He began researching the end-Permian mass extinction in the early 1980's and has traveled many times to China, South Africa, and Europe seeking its causes.

2-12-18 Ancient ozone holes may have sterilized forests 252 million years ago
Barren trees could have collapsed food webs, leading to Earth’s greatest mass extinction. Volcano-fueled holes in Earth’s ozone layer 252 million years ago may have repeatedly sterilized large swaths of forest, setting the stage for the world’s largest mass extinction event. Such holes would have allowed ultraviolet-B radiation to blast the planet. Even radiation levels below those predicted for the end of the Permian period damage trees’ abilities to make seeds, researchers report February 7 in Science Advances. Jeffrey Benca, a paleobotanist at the University of California, Berkeley, and his colleagues exposed plantings of modern dwarf pine tree (Pinus mugo) to varying levels of UV-B radiation. Those levels ranged from none to up to 93 kilojoules per square meter per day. According to previous simulations, UV-B radiation at the end of the Permian may have increased from a background level of 10 kilojoules (just above current ambient levels) to as much as 100 kilojoules, due to large concentrations of ozone-damaging halogens spewed from volcanoes (SN: 1/15/11, p. 12). Exposure to higher UV-B levels led to more malformed pollen, the researchers found, with up to 13 percent of the pollen grains deformed under the highest conditions. And although the trees survived the heightened irradiation, the trees’ ovulate cones — cones that, when fertilized by pollen, become seeds — did not. But the trees weren’t permanently sterilized: Once removed from extra UV-B exposure, the trees could reproduce again.

2-7-18 The worst mass extinction may have begun with mass sterilisation
There seems to have been a surge in ultraviolet radiation during the Permian extinction 252 million years ago, and it might have left plants infertile rather than kill them. We may have misunderstood the mother of all extinctions. The gargantuan Permian extinction has been blamed on massive volcanic eruptions that killed swathes of organisms, but the eruptions may instead have had an insidious effect: sterilisation. Organisms may not have been killed outright, but if they could not reproduce their species were still doomed. Almost all complex life died 252 million years ago at the end of the Permian period. The causes have long been debated. About a decade ago geologists began noticing something odd about fossil pollen from the time. An unusually high number of the pollen grains were malformed or under-developed. That might be because the volcanic activity at the time released ozone-destroying chemicals into the atmosphere. As a result, more of the sun’s harmful ultraviolet-B (UV-B) radiation reached Earth’s surface. The UV-B would have stressed plants, particularly the abundant conifers and seed ferns, which suffered during the extinction. To mimic this environmental upheaval, Jeffrey Benca, Ivo Duijnstee and Cindy Looy at the University of California, Berkeley exposed 18 dwarf conifers to elevated UV-B levels for 56 days. The tiny trees produced elevated levels of malformed pollen, as predicted. But something unexpected happened. Although the trees survived UV-B exposure, they were all rendered infertile throughout. The pines made seed cones, but these died before they grew large enough to be fertilised. “The shrivelled-up seed cones were a big surprise,” says Looy.

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Extinction
How Life on Earth Nearly Ended 250 Million Years Ago
By Douglas H. Erwin

Sioux Falls Scientists endorse Extinction for exploring how and why 95%
of life went extinct 250 million years ago in the greatest mass extinction.