9. What happened to dinosaurs?

2006

28 November 2006. New York Times. Marine Life Leaped From Simple to Complex After Greatest Mass Extinction. By Andrew C. Revkin. Excerpt: At least five mass extinctions, most presumably caused by asteroids that struck the earth, have transformed global ecology in the half-billion years since the emergence of multicelled life, lopping entire branches from the evolutionary tree and causing others to flourish. The greatest "great dying," 251 million years ago, erased 95 percent of species in the oceans (and most vertebrates on land). But new research suggests that it was followed by an explosion of complexity in marine life, one that has persisted ever since. Moreover, it happened quite suddenly... The shift to complicated, interrelated ecosystems was more like a flip of a switch than a slow trend. The researchers detected the change by analyzing records of marine fossils from 1,176 sites around the world, which are part of a new international archive, the Paleobiology Database (pbdb.org).

23 September 2006. DINOSAURS' CLIMATE SHIFTED TOO, REPORT SHOWS. Ancient rocks suggest dramatic climate changes during the dinosaur-dominated Mesozoic Era, a time once thought to have been hot and humid. NASA Earth Observatory.

2005

20 September 2005. Fossils Offer Support for Meteor's Role in Dinosaur Extinction. By WILLIAM J. BROAD. For more than a decade, the standard view has envisioned a speeding object from space that crashed into the earth and kicked up enough dust and rock around the globe to blot out the sun. The smoking gun seemed to be the discovery beneath the Yucatán peninsula of Mexico of a 110-mile-wide crater called Chicxulub, after a nearby town. But lately, doubters have argued that Chicxulub formed 300s,000 years before the mass extinction - too early to have played a role in the demise of the dinosaurs and hundreds of other plant and animal species that vanished at the end of the Cretaceous. ...Now, in the September issue of Geology, the scientists, from Spain, Cuba and Mexico, report that they have discovered a highly disturbed bed of fossils that bears numerous signatures of Chicxulub's mayhem. The date of the disturbance, 65 million years ago, is exactly at the end of the Cretaceous. ...Starting around 2000, Dr. Alegret and her European colleagues repeatedly sought work permits for a nearby hill but always met with stultifying delays, if not outright rejections. Finally, they slipped into the site with their Cuban colleagues, going in late 2000, 2002 and 2003. ...A rocky outcrop on the hill showed an exposed bed of sedimentary rock made up of broken bits of minerals and fossils. It was more than 30 feet thick. The team took 66 samples. Examination with microscopes showed numerous signs of cosmic violence, including quartz deformed by high temperatures and pressures, as well as tiny spheres of glass, both clearly debris from a spectacular fireball. Microscopic study also revealed the presence of thousands of tiny fossil creatures, most especially foraminifera. ... Forams, as they are known, evolve so fast that geologists, paleontologists and oil companies use their shifting appearance as reliable guides to geologic dating. "They told the age of the sediments," Dr. Alegret said. "So we've definitely confirmed the age of these deposits." At the end of the Cretaceous, the rocky bed now in Cuba formed on the ocean bottom at a depth of perhaps 3,300 feet, over a few days or weeks as tons of debris rained down from the sky and huge waves generated by the Chicxulub event washed land out to sea. "It was geologically instantaneous," Dr. Alegret said of the deposit's formation.

10 March 2005. Mass extinction comes every 62 million years, UC physicists discover. David Perlman, SF Chronicle Science Editor. Excerpt: With surprising and mysterious regularity, life on Earth has flourished and vanished in cycles of mass extinction every 62 million years, say two UC Berkeley scientists who discovered the pattern after a painstaking computer study of fossil records going back for more than 500 million years. Their findings are certain to generate a renewed burst of speculation among scientists who study the history and evolution of life. Each period of abundant life and each mass extinction has itself covered at least a few million years -- and the trend of biodiversity has been rising steadily ever since the last mass extinction, when dinosaurs and millions of other life forms went extinct about 65 million years ago....Richard Muller and his graduate student, Robert Rohde, are publishing a report on their exhaustive study in the journal Nature today, and in interviews this week, the two men said they have been working on the surprising evidence for about four years. "We've tried everything we can think of to find an explanation for these weird cycles of biodiversity and extinction," Muller said, "and so far, we've failed." But the cycles are so clear that the evidence "simply jumps out of the data," said James Kirchner, a professor of earth and planetary sciences on the Berkeley campus who was not involved in the research but who has written a commentary on the report that is also appearing in Nature today..

2004

26 December 2004. About tsunami from asteroidal impacts: Deep-sea waves generated at contact by asteroids varying in diameter from 1-100km (unaffected by interaction with sea floor) could reach heights of about 1 km, according asteroidal impact modeling studies (e.g. Gisler, Weaver, et al. 2002). This would translate into multi-km wave heights upon arrival in shallow/shore waters. Thankfully, these are rather rare events, even by geological standards.

26 August 2004. Ground Zero for the "Great Dying"? - J. KELLY BEATTY, Sky & Telescope magazine. Excerpt: IT'S BEEN NEARLY a quarter century since geologists realized that a colossal impact contributed to (and probably caused) the demise of the dinosaurs and most of Earth's other species 65 million years ago. ...In the years since, researchers have sought evidence linking impacts with other mass extinctions throughout geologic history. The worst of these die-offs brought an abrupt end to the vibrant Permian period 251 million years ago, nearly sterilizing Earth by wiping out 90 percent of all marine species and 70 percent of those on land in less than 160,000 years. No compelling explanation for the Permian-Triassic extinction - widely called the "Great Dying" - has yet gained favor. But recent research suggests that, coincidence or not, the Great Dying was accompanied by a Great Wallop. Fallout from a major blast has been found at the Permian-Triassic boundary in Antarctica, Australia, China, and Japan (S&T: June 2001, page 26). Now seven geoscientists, led by Luaim Becker (University of California, Santa Barbara), think they've found "ground zero" on the northwest margin of Australia. In the online journal ScienceExpress for May 13th, they argue that the Bedout High, a broad, lava-covered dome that today lies deeply buried beneath sea-floor sediment, is actually the uplifted center of a crater comparable in size to the huge Yucatan scar....But some impact specialists are skeptical For example, Andrew Glikson (Australian National University) found no evidence for impact-induced shock when he examined one of the Bedout drill cores. And none of the Permian-Triassic boundary layers show a pronounced excess of iridium, a telltale trace element that's rare in Earth's crust but common in meteorites. Meanwhile, debate continues over whether the Permian-Triassic extinction was instead caused by a massive outflow of lava in what is now Siberia. All told, volcanoes disgorged some 2 million cubic kilometers of molten rock and inundated an area the size of Europe. That eruption, proponents argue, set off an abrupt green house effect or other climatic upheaval.

14 May 2004. Did an Impact Trigger the "Great Dying"? By J. Kelly Beatty, Sky & Telescope magazine. It's been nearly a quarter century since geologists realized that a colossal impact contributed to (and probably caused) the decimation of the dinosaurs and vast numbers of Earth's other species 65 million years ago. Eventually this event's smoking gun, a crater some 180 kilometers across, was discovered beneath what is now Mexico's Yucatán Peninsula. In the years since researchers have sought evidence linking impacts with other mass extinctions of life throughout geologic history. The biggest of these, 251 million years ago, ended the vibrant Permian period and nearly left Earth sterile: 90 to 95 percent of all species died within a geologic blink of an eye. No compelling explanation for the Permian-Triassic extinction - widely called the "Great Dying" - has yet gained favor. Now seven geoscientists, led by Luann Becker (University of California, Santa Barbara), believe they've identified evidence of a huge impact on the northwest margin of Australia. In the May 13th ScienceExpress, they claim that the Bedout High, a broad plateau now deeply buried beneath seafloor sediment, is actually the uplifted center of an impact crater comparable in size to the Yucatán's huge scar.

13 May 2004 NASA RELEASE: 04-159 -- Evidence Of Meteor Impact Found Off Australian Coast. An impact crater believed to be associated with the " Great Dying," the largest extinction event in the history of life on Earth, appears to be buried off the coast of Australia.

24 February 2004. Scientists want to be ready to block asteroid from hitting Earth. GARDEN GROVE, California (AP) -- The asteroid believed to have wiped out dinosaurs 65 million years ago was rare but hardly unique, say scientists gathered to discuss ways of aggressively defending our planet from another such space rock, including by detonating nukes in space. Asteroids capable of inflicting damage on a global scale hit the Earth roughly every million years, and we shouldn't dawdle in developing a method of deflecting them, say the scientists attending a four-day planetary defense conference in suburban Orange County.

2003

17 January 2003. Columbia University Research Finds Correlation Between Meteorite and Comet Impacts and an Increase in Volcanic Activity Development. 10 Major Episodes of Extraterrestrial Impacts Found to Correlate with 9 Major Episodes of Volcanism. Earth Institute at Columbia University; Mary Tobin; 845-365-8607

2002

11 December 2002. New Scientist -- Earth's volcanism linked to meteorite impacts. Large meteorite impacts may not just throw up huge dust clouds but also punch right through the Earth's crust, triggering gigantic volcanic eruptions. The idea is controversial, but evidence is mounting that the Earth's geology has largely been driven by such events. This would also explain why our planet has so few impact crater remnants.

December 2002. Did a Comet Swarm Kill the Dinosaurs? by DAVID TYTELL, Sky & Telescope magazine, p. 24. IN 1991 A MODERN SCIENTIFIC "WHODUNIT" WAS SOLVED WHEN geologists identified a deeply buried, 180-kilometer-Wide crater in the Yucatan peninsula. Now known as Chicxulub, the scar resulted from the impact of a 10-km asteroid or comet nucleus 65 million years ago. Geologic evidence indicates that the impact triggered global tidal waves, worldwide firestorms, and massive earthquakes. It also left a worldwide layer of extraterrestrial dust. When Earth finally returned to normal, the dinosaurs and the majority of all then-living species had gone extinct, opening the way for mammals to diversify and dominate Earth. ...Now a new study suggests that Chicxulub may not have been an isolated event. Rather, the dinosaurs may have been the victims of a one-two punch.

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