Posted on 11/25/2006 3:34:53 PM PST by SunkenCiv
The earth experienced its biggest mass extinction about 250 million years ago, an event that wiped out an estimated 95% of marine species and 70% of land species. New research shows that this mass extinction did more than eliminate species: it fundamentally changed the basic ecology of the world's oceans... Specifically, the data and analyses concern models of relative abundance found in fossil communities throughout the Phanerozoic. The ecological implications are striking. Simple marine ecosystems suggest that bottom-dwelling organisms partitioned their resources similarly. Complex marine ecosystems suggest that interactions among different species, as well as a greater variety of ways of life, affected abundance distributions. Prior to the end-Permian mass extinction, both types of marine ecosystems (complex and simple) were equally common. After the mass extinction, however, the complex communities outnumbered the simple communities nearly 3:1.
(Excerpt) Read more at physorg.com ...
Scientists Find Signs of Meteor Crash That Led to Extinctions in Era Before DinosaursScientists examining the layer of sediment corresponding to the die-offs discovered concentrations of the sturdy, soccer-ball-shaped carbon molecules, buckminsterfullerenes, or buckyballs. Within the buckyballs was a mix of helium and argon gases similar to that found in certain stars but unlike anything that could form naturally on Earth. A few inches below and above the extinction layer, they found very few buckyballs... Recent work indicates the extinctions happened quickly, within 100,000 years. That led to speculation that an asteroid or comet impact might be to blame... The buckyballs and gases were found in samples from Japan and China, while a sample from Hungary was almost devoid of buckyballs. Other scientists said that samples from other regions would be needed to confirm the findings and to rule out other potential sources, like cosmic dust... Dr. Robert J. Poreda, a professor of earth and environmental sciences at the University of Rochester and another author on the Science paper, said the energy released by the meteor, estimated at four to eight miles wide, would have been equivalent to a magnitude-12 earthquake... Dr. Becker, Dr. Poreda and their colleagues had previously found buckyballs at an impact crater in Sudbury, Canada, and in two meteorites. They have also found buckyballs containing similar types of gases in sediments dating from the dinosaur extinctions.
by Kenneth Chang
February 23, 2001
Physics News UpdateAn asteroid impact may have caused the mass extinction that occurred at the boundary between the Permian and Triassic periods 250 million years ago, said Michael Rampino of NYU at the AGU meeting. He asserted that he has found evidence---in the form of gravity anomalies and certain rock deposits---for such an impact in the South Atlantic, in an area where, many scientists believe, South America, Africa, and other land masses fit together in the primordial supercontinent called Gondwanaland. Rampino claims that the gradual breakup of Gondwanaland into present-day continents may have been initiated by the catastrophic impact. Another scientist at the meeting, Verne Oberbeck of NASA/Ames also believes an impact may have sundered Gondwanaland and that, in general, impacts should be given more credit for shaping earlier Earth geology. In particular, he believes that the small rock sediments called tillites, usually thought to result from the grinding and plowing action of glaciers, may in part be debris from impacts. Consequently, Oberbeck suggested, there might have been fewer glacial periods than is usually believed. Rampino went so far as to say that all tillites are of impact origin. Unlike the theory that describes the KT (Cretaceous-Tertiary) catastrophe 65 million years ago (when the dinosaurs became extinct) in terms of an asteroid impact, the notion that the PT catastrophe was caused by an impact or that tillites result from impacts is anything but a majority opinion; indeed, many scientists at the meeting were skeptical about Rampino's and Oberbeck's ideas. Thomas Crowley of the Applied Research Corp. (409-846-1403), a paleo-climatologist, said that his reaction to the proposed impact origin of tillites was one of "considerable disbelief, bordering on incredulity." For one thing, he said, tillite deposits are too extensive over time and physical extent to have been caused by an impact.
by Phillip F. Schewe and Ben Stein
December 14, 1992
American Institute of Physics Bulletin of Physics News
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kewl. so, who was there to record the events?
YEC INTREP
November 8, 2006
Dr. Peter Wagner
Dept. of Geology, The Field Museum
"Relative Abundance Distributions in the Fossil and their Implications for Major Extinction Events"
http://www.fieldmuseum.org/research_collections/rescol_seminars.htm
(other than that, I found nothing on the site, such as the press release that was used by PhysOrg)
There is no record of events. However, there were 30 families in the fossil record before and 3 after, so an event is surmised.
http://pondside.uchicago.edu/ceb/faculty/wagner.html
Wagner, P. J., (In press).
Patterns of morphologic diversification among the Rostroconchia. Paleobiology 23. [I could not access it from here, maybe from the library]
Wagner, P. J., (In press).
Phylogenetics of the earliest gastropods. Smithsonian Contributions to Paleobiology.
http://www.sil.si.edu/smithsoniancontributions/Paleobiology/pdf_hi/SCtP-0088.pdf
Phylogenetic Relationships of the Earliest Anisostrophically Coiled Gastropods
Peter J. Wagner
152 pages, 37 figures, 3 tables
2002 (Date of Issue: 30 January 2002)
Number 88, Smithsonian Contributions to Paleobiology
Display: PDF (Hi-Res) (57,217 kb) | | Full Record (from SIRIS) not yet available
Abstract
In order to explore the phylogenetic relationships among early gastropods, cladistic analyses were conducted of nearly 300 "archaeogastropod" species known from the latest Cambrian through the Silurian. The study includes an extended outgroup analysis of Cambrian molluscs. The resulting estimates of gastropod phylogeny differ not only from traditional ideas about early gastropod relationships, but also from most alternative notions. Outgroup analyses suggest that gastropods had ancestors among the Tergomya ( =Monoplacophora of many workers) of the Middle or Late Cambrian. Putative gastropods from older strata (e.g., the Pelagiellida and early Onychochilidae) apparently are not closely related to gastropods. The hypothesized ancestor of gastropods possessed dextral-coiling, septation, a deep sinus, and a peripheral band. An anal slit is commonly described as a synapomorphy of gastropods that many clades subsequently lost; however, this study suggests that the slit is a rare, highly derived, and polyphyletic character among early Paleozoic species, and that the ancestors of most "advanced" clades (e.g., the Apogastropoda) never had slits.
This study suggests that two major subclades evolved by the earliest Ordovician. The diagnoses and definitions of these two subclades best correspond to the traditional diagnoses and definitions of the Euomphalina and Murchisoniina. The Pleurotomarioidea is not a paraphyletic ancestral taxon as typically suggested, but instead it is a polyphyletic assemblage derived multiple times from "euomphalinae" and "murchisoniinae" species. The Bellerophontina is at least diphyletic, as the taxon includes both the ancestors of "archaeogastropods" and a clade of planispiral species that is secondarily derived from "archaeogastropods." Macluritoids sensu stricto represent a restricted subclade of the "euomphalinae"; other supposed macluritoids evolved among different euomphalinae subclades or are not gastropods. Early Paleozoic species previously classified as caenogastropods (i.e., the Loxonematoidea and Subulitoidea) represent separate murchisoniinae subclades, with some putative members of the Subulitoidea derived within the Loxonematoidea. Early Paleozoic species assigned to the Trochoidea also represent several subclades, with most of those clades having evolved from the "euomphalinae."
An extensive taxonomic revision is presented, which removes all early Paleozoic taxa from the Pleurotomariina and broadly expands the definitions of the Euomphalina and Murchisoniina.
Earth is not capitalized. Did you note the earlier thread of the absence of literature these days?
Subject to interpretation, of course. Or no?
It's all George Bush's fault
Helen Thomas...
They have a 2 hour special on the Discover Channel, which discusses evolution before the Age of Dinosaurs. It runs from 8 to 10 pm tonight and is a repeat. At about 9:30 it will talk about a non-impact theory for the great Permian extinction.
Of course ... just like Hurricane Katrina.
IOW, he's one of *those*. The human relationship with the Earth is much less than that of a tick to a dog.Earth hit by 'mass extinction'"We think these are the first analyses of this type at this large scale," said Peter Wagner, associate curator of fossil invertebrates at The Field Museum and lead author of the study, who worked with Matthew Kosnik of James Cook University... The results of the study could provide a warning on how we treat the ecosystem now, the experts said. "Studies by modern marine ecologists suggest that humans are reducing certain marine ecosystems to something reminiscent of 550 million years ago, prior to the explosion of animal diversity," Mr Wagner said. "The asteroid that wiped out the dinosaurs couldn't manage that."
Australia Sunday Telegraph
Agence France-Presse
November 24, 2006
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