-Caveat Lector- http://www.space.com/scienceastronomy/solarsystem/impact_rebound_010309.html Cosmic Smack Encourages Life To Go Forth and Multiply By Robert Roy Britt Senior Science Writer posted: 02:00 pm ET 08 March 2001 A discovery that earthly flora and fauna rebound and advance rapidly after catastrophic collisions by space rocks highlights the resourcefulness of life and bolsters a growing suspicion that evolution does its best work in extreme crises. When a comet or asteroid smacked Earth 65 million years ago, the dinosaurs bid farewell. They could not adapt to a world remade by the extreme ecological violence. They were not alone. Roughly two-thirds of all life on Earth vanished. But new species sprang forth from the catastrophe, evolving quickly to fill new niches of climate, water and soil conditions. A new study examined extraterrestrial dust to pin down just how quickly. In a mere 10,000 years -- the blink of an eye on a geologic time scale -- the planet was repopulated by newly evolved versions of tiny critters that had been mostly wiped out by the impact, according to a study published in the March 9, 2001 issue of the journal Science. "We simply don't get significant evolutionary change without an extraterrestrial cause." -- Luann Becker, University of Washington Around the globe, layers of sediment deposited by ancient seas hold a record of what has lived and died on Earth going back billions of years. And when scientists dig, they usually find a layer less than an inch (2 centimeters) thick that contains virtually no fossils and is thought to correspond to the time of the mass extinction. Careful analysis recently yielded a surprisingly short estimate for the period of time represented by those fossil-free layers, and the new thinking is that new species arise and evolve much more quickly than scientists had imagined. The mass extinction came, the thinking goes, after a cosmic impact in what is now Mexico's Yucatan Peninsula shook the planet and sent up a choking mix of dust and chemicals that darkened the global skies for possibly decades. Most plankton and many tropical marine invertebrates, especially reef-dwellers, perished in the event, along with many species of land animals and plants. Until now, some researchers have supposed it took hundreds of thousands of years for many species to die out as the impact combined with other killing mechanisms, such as long-term volcanic activity or changing sea levels. Clues in space dust The new research measured space dust laid down in the ancient sediment. Packed inside the dust, and revealing its extraterrestrial origin, was helium 3, an isotope of helium that is rarely found on Earth except when it originated from space. The dust, deposited at a steady rate over millions of years, revealed how much time passed -- just 10,000 years -- between the demise of vast numbers of marine organisms and the rebirth of new ones. "These types of severe mass extinctions seem to pave the way for life to more or less reinvent itself and come back even stronger and more capable of adapting to extreme environmental change," said the University of Washington's Luann Becker, who was not involved in the study. "We simply don't get significant evolutionary change without an extraterrestrial cause." Becker, who in February provided evidence that an earlier mass extinction was caused by a space rock, said the new study is consistent with what paleontologists have been suggesting in recent years: The worst extinctions seem to be rapid events. And she said the ability of organisms to re-emerge quickly might shed light on how life evolved on Earth in the beginning, billions of years ago, when the planet was regularly pummeled by comets and asteroids. Ruling out other causes of extinction The evidence for the short recovery is recorded in exposed layers of Earth that formed at the bottom of ancient seas about 100 miles (160 kilometers) north of what is now Rome. Prior to the impact, marine organisms lived and died in droves, and their corpses helped create a global coffin of limestone that built up over the eons. Abruptly, the limestone layers stop, covered over by thin layer of clay that formed in the virtual absence of marine life. Above that clay the limestone sharply resumes, which means marine organisms had repopulated the Earth, and had done so in a rather sudden manner. Researchers have long known the thickness of this relatively fossil-free layer of clay, but they have argued over how much time passed during its creation. The clay layer marks the boundary between the Cretaceous and Tertiary Eras of geologic time. "And now we know how far apart they are in time," said Kenneth Farley, a Caltech geochemist and coauthor of the Science paper discussing the research. The finding implies that the impact itself, along with the severe climatic and geologic effects it generated, was the primary reason the dinosaurs and other species perished. Others have speculated that ongoing volcanic activity might have been a significant contributor, but Farley and others say that volcanism would have been a slower killing mechanism, requiring 100,000 years or more to deal the amount of death now thought to have occurred in less than 10,000 years. "I think it rules out long-term progressive kinds of [extinction] processes like sea-level change or volcanism," Farley said in a telephone interview. The finding would also rule out multiple impacts as the cause of the extinction event. "There's been a longstanding debate whether the mass extinctions at the [Cretaceous-Tertiary] boundary were caused by a single impact or maybe a swarm of millions of comets," said Sujoy Mukhopadhyay, a graduate student at Caltech and lead author of the paper. Alessandro Montanari of the Geological Observatory in Apiro, Italy, also worked on the study. The fossils of critters that emerged, survived and thrived in just 10,000 years now speak volumes about the tight relationship between life and cosmic catastrophe. "It's clear when you look at the species before and after, that there are new [species] after the impact," Farley said. "Surely they've been culled from whatever population existed before the event. They haven't re-evolved from scratch. It shows how fast new species can populate a niche." This rapid diversification of species is "particularly exciting because it implies that impacts might have accelerated the evolution of life on Earth," said Matthew Genge, a researcher at the London Natural History Museum. Details in the dust The chronology of death and rebirth was created by a steady supply of space dust that works its way to Earth from farther out in the solar system. Asteroids located mostly between Mars and Jupiter, in a region known as the Asteroid Belt, bump and grind over time and create large amounts of dust. And comets that pass through the inner solar system release spurts of dust, which is spread through space over time. These processes have been generating relatively consistent amounts of dust for many millions of years. Drawn toward the Sun by gravity, this dust captures and carries a high concentration of helium 3 that is riding outward from the Sun on the solar wind, a stream of energized particles. The dust brings the helium 3 to Earth in miniscule but near-constant amounts. Some of it is stripped from the dust during entry into the atmosphere, but a steady fraction makes it to the surface. Genge, who studies the sources and effects of cosmic dust and meteorites, said using the dust to create a chronology is a very reliable method. Comet or asteroid? The new research might also shed light on the origin of the space rock that caused the extinction. Genge said the findings suggest the impactor was not a "short-period" comet (like Comet Halley that regularly orbits the Sun). Periodic comets rarely spend more than a few tens of thousands of years in the inner solar system, explains Genge, before being swallowed by the Sun. "We should see a gradual increase in the amount of helium 3 brought in by dust just before the impact and a decrease afterwards if it was a periodic comet," he told SPACE.com. "This is, therefore, evidence that the [Cretaceous-Tertiary] impactor was either an asteroid or a long-period comet." Long-period comets originate as far as a third of the way to the nearest star in a halo of objects called the Oort Cloud, which surrounds our solar system. They can be tossed our way by the gravitational effects of passing stars. More controversial claims have been made that these comets might be hurled Earthward by gravitational changes when our solar system passes through the dense plane of the Milky Way Galaxy, which it does periodically as we orbit around the galactic center. Researchers have tried to tie this periodicity to an apparent cycle of mass extinctions occurring every 26 million years or so, though there is no agreement on the issue. "It is thus interesting to ponder that if the position and motion of a planetary system controls the rate at which impacts occur, then it may also influence the biological evolution in habitable planetary environments," Genge said. "Too many impacts, and evolution may be stalled; too few, and it may only crawl along." <A HREF="http://www.ctrl.org/">www.ctrl.org</A> DECLARATION & DISCLAIMER ========== CTRL is a discussion & informational exchange list. Proselytizing propagandic screeds are unwelcomed. Substance—not soap-boxing—please! These are sordid matters and 'conspiracy theory'—with its many half-truths, mis- directions and outright frauds—is used politically by different groups with major and minor effects spread throughout the spectrum of time and thought. That being said, CTRLgives no endorsement to the validity of posts, and always suggests to readers; be wary of what you read. CTRL gives no credence to Holocaust denial and nazi's need not apply. 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