Post by 1dave on Aug 18, 2018 20:28:02 GMT -5
The Permian time period from 290 to 250 million years ago, became one of the greatest times of advances, diversity, and flourishing of life forms on land and in the sea.
Mammals were on their way to take over the planet.
It started out as the best of times, but ended up being the worst of times.
In the sea - ammonoids, brachiopods, cephalopods, echinoderms, mollusks, and trilobites prospered. The lobe-finned and spiny fishes that gave rise to the amphibians of the Carboniferous were being replaced by true bony fish. Sharks and rays continued in abundance.
On land - diverse plants, fungi, arthropods (invertebrate insects, spiders, crustaceans) and various types of tetrapods (four-limbed vertebrates ) thrived. About the middle of the Permian a major transition in vegetation began with the evolution of swamp-loving lycopod trees of the Carboniferous, such as Lepidodendron and Sigillaria.
The Permian also saw the radiation of many important conifer groups, including the ancestors of many present-day families. Rich forests were present in many areas, with a diverse mix of plant groups. The southern continent saw extensive seed fern forests of the Glossopteris flora. Oxygen levels were probably high there. The ginkgos and cycads also appeared during this period.
Primitive forms of Odonata were the dominant aerial predators and probably dominated terrestrial insect predation as well. True Odonata ( dragonflies) appeared in the Permian, and all were semi-aquatic insects (aquatic immature stages, and terrestrial adults), as are all modern odonates. Their prototypes are the oldest winged fossils, dating back to Devonian Times, and are different in several respects from the wings of other insects. Fossils suggest they may have possessed many modern attributes even by the late Carboniferous, and it is possible that they captured small vertebrates, for at least one species had a wing span of 71 cm (28 in). Several other insect groups appeared during the Permian, including the Coleoptera (beetles) and Hemiptera (true bugs).
Amphibian and Synapsid (reptiles with increasingly mammalian characteristics, include the ancestors of mammals) fauna
The Permian period saw the development of a fully terrestrial fauna and the appearance of the first large herbivores and carnivores. Permian amphibians consisted of temnospondyli, lepospondyli and batrachosaurs. The special adaptations of reptiles enabled them to flourish in the drier climate of the Permian and they grew to dominate the vertebrates.
It was the high tide of the anapsids in the form of the massive Pareiasaurs and host of smaller, generally lizard-like groups. A group of small reptiles, the diapsids, began to abound. These were the ancestors to most modern reptiles and the ruling dinosaurs as well as pterosaurs and crocodiles.
The synapsid, early ancestors to mammals, also thrived at this time. Synapsids included some large members such as Dimetrodon.
Early Permian terrestrial faunas were dominated by amphibians, pelycosaurs (reptiles having a line of long bony spines along the back supporting a sail-like crest), and diadectids (the first herbivorous tetrapods).
The middle Permian was dominated by primitive therapsids (a group of synapsids that includes mammals and their ancestors).
The late Permian was dominated by more advanced therapsids such as gorgonopsians and dicynodonts (herbivorous animals with two tusks, hence their name, which means 'two dog tooth'). Mammals are the only surviving synapsids.
Towards the very end of the Permian the first archosaurs (a group of diapsid amniotes whose living representatives consist of birds and crocodilians. This group also includes all extinct dinosaurs, extinct crocodilian relatives, and pterosaurs) appeared, a group that would give rise to the crurotarsans (reptiles that includes the archosaurs and the extinct, crocodile-like phytosaurs.) and the dinosaurs in the following period.
The Permian ended with the greatest catastrophe and destruction of life of all times.
More than 95 percent of marine species became extinct and more than 70 percent of land animals. Fossil beds in the Italian Alps show that plants were hit just as hard as animal species.
www.nationalgeographic.com/science/prehistoric-world/permian-extinction/
www.geologyin.com/2015/12/permian-triassic-boundary.html
news.osu.edu/big-bang-in-antarctica----killer-crater-found-under-ice/
May 31, 2006 Big Bang In Antarctica -- Killer Crater Found Under Ice
Ancient mega-catastrophe paved way for the dinosaurs, spawned Australian continent
COLUMBUS, Ohio -- Planetary scientists have found evidence of a meteor impact much larger and earlier than the one that killed the dinosaurs -- an impact that they believe caused the biggest mass extinction in Earth's history.
The 300-mile-wide crater lies hidden more than a mile beneath the East Antarctic Ice Sheet. And the gravity measurements that reveal its existence suggest that it could date back about 250 million years -- the time of the Permian-Triassic extinction, when almost all animal life on Earth died out.
science.nasa.gov/science-news/science-at-nasa/2002/28jan_extinction
Above: What the world looked like 250 million years ago. Image credit: Chris Scotese. [more]
Mammals were on their way to take over the planet.
It started out as the best of times, but ended up being the worst of times.
In the sea - ammonoids, brachiopods, cephalopods, echinoderms, mollusks, and trilobites prospered. The lobe-finned and spiny fishes that gave rise to the amphibians of the Carboniferous were being replaced by true bony fish. Sharks and rays continued in abundance.
On land - diverse plants, fungi, arthropods (invertebrate insects, spiders, crustaceans) and various types of tetrapods (four-limbed vertebrates ) thrived. About the middle of the Permian a major transition in vegetation began with the evolution of swamp-loving lycopod trees of the Carboniferous, such as Lepidodendron and Sigillaria.
The Permian also saw the radiation of many important conifer groups, including the ancestors of many present-day families. Rich forests were present in many areas, with a diverse mix of plant groups. The southern continent saw extensive seed fern forests of the Glossopteris flora. Oxygen levels were probably high there. The ginkgos and cycads also appeared during this period.
Primitive forms of Odonata were the dominant aerial predators and probably dominated terrestrial insect predation as well. True Odonata ( dragonflies) appeared in the Permian, and all were semi-aquatic insects (aquatic immature stages, and terrestrial adults), as are all modern odonates. Their prototypes are the oldest winged fossils, dating back to Devonian Times, and are different in several respects from the wings of other insects. Fossils suggest they may have possessed many modern attributes even by the late Carboniferous, and it is possible that they captured small vertebrates, for at least one species had a wing span of 71 cm (28 in). Several other insect groups appeared during the Permian, including the Coleoptera (beetles) and Hemiptera (true bugs).
Amphibian and Synapsid (reptiles with increasingly mammalian characteristics, include the ancestors of mammals) fauna
The Permian period saw the development of a fully terrestrial fauna and the appearance of the first large herbivores and carnivores. Permian amphibians consisted of temnospondyli, lepospondyli and batrachosaurs. The special adaptations of reptiles enabled them to flourish in the drier climate of the Permian and they grew to dominate the vertebrates.
It was the high tide of the anapsids in the form of the massive Pareiasaurs and host of smaller, generally lizard-like groups. A group of small reptiles, the diapsids, began to abound. These were the ancestors to most modern reptiles and the ruling dinosaurs as well as pterosaurs and crocodiles.
The synapsid, early ancestors to mammals, also thrived at this time. Synapsids included some large members such as Dimetrodon.
Early Permian terrestrial faunas were dominated by amphibians, pelycosaurs (reptiles having a line of long bony spines along the back supporting a sail-like crest), and diadectids (the first herbivorous tetrapods).
The middle Permian was dominated by primitive therapsids (a group of synapsids that includes mammals and their ancestors).
The late Permian was dominated by more advanced therapsids such as gorgonopsians and dicynodonts (herbivorous animals with two tusks, hence their name, which means 'two dog tooth'). Mammals are the only surviving synapsids.
Towards the very end of the Permian the first archosaurs (a group of diapsid amniotes whose living representatives consist of birds and crocodilians. This group also includes all extinct dinosaurs, extinct crocodilian relatives, and pterosaurs) appeared, a group that would give rise to the crurotarsans (reptiles that includes the archosaurs and the extinct, crocodile-like phytosaurs.) and the dinosaurs in the following period.
The Permian ended with the greatest catastrophe and destruction of life of all times.
More than 95 percent of marine species became extinct and more than 70 percent of land animals. Fossil beds in the Italian Alps show that plants were hit just as hard as animal species.
www.nationalgeographic.com/science/prehistoric-world/permian-extinction/
www.geologyin.com/2015/12/permian-triassic-boundary.html
I remain perplexed that most investigators remain ignorant of the 250 Ma Wilkes Land, Antarctica Impact Crater that is 500 Km in diameter. That is what drove all the oxygen out of the oceans, initiated the Siberian Flood Volcanoes, and started the breakup of Pangea.
news.osu.edu/big-bang-in-antarctica----killer-crater-found-under-ice/
May 31, 2006 Big Bang In Antarctica -- Killer Crater Found Under Ice
Ancient mega-catastrophe paved way for the dinosaurs, spawned Australian continent
COLUMBUS, Ohio -- Planetary scientists have found evidence of a meteor impact much larger and earlier than the one that killed the dinosaurs -- an impact that they believe caused the biggest mass extinction in Earth's history.
The 300-mile-wide crater lies hidden more than a mile beneath the East Antarctic Ice Sheet. And the gravity measurements that reveal its existence suggest that it could date back about 250 million years -- the time of the Permian-Triassic extinction, when almost all animal life on Earth died out.
The Cause of the end-Permian Extinction: Five Theories
There are five leading theories that attempt to explain what happened at the end of the Permian. There are numerous other theories (such as global cooling; see Stanley, 1987) and "sub-theories," which modify the main theories. But the main theories are those which have attracted the most attention from scientists. These are: 1. the impactor (bolide) theory, 2. the volcanism theory, 3. the regression theory, 4. the oceanic overturn theory, and 5. the methane catastrophe theory.
1. Impactor
The impactor theory is, of course, inspired by the success of the Alvarez's explanation for the end-Cretaceous catastrophe. Clearly the impact from this asteroid or comet caused an extraordinary catastrophe for many organisms. Obviously, according to impactor advocates, an even larger impactor would have the energy to do even greater damage to the biosphere. With many large objects (both asteroids and comets) meandering around and through the inner solar system, there are plenty of potential impactors. Consequently, the impactor theory has had a strong appeal and needs to be examined seriously.
The problem with the impactor proposal, however, is that there has been no evidence to support it. There is no iridium layer, as found at the Cretaceous-Tertiary boundary. There is no accepted evidence for shocked quartz, though some have claimed to have found such, but the quality of their specimens has been unconvincing. There are no microtektites -- or the clay spherules which the microtektites by now would have weathered into. (Spherules from the Emeishan volcanic episode [258 to 254 million years ago; Xu, 2004] in the South China area have been found, but obviously these have nothing to do with any alleged impact.) There are no tsunami deposits that record a great impact in the ocean. No impact crater has been located.
Unfortunately, the theory's strong appeal has led some to believe that there is -- or must be -- evidence. One geological chart actually indicates the size of the impactor that the chart's designers (without evidence) knew must have caused the end-Permian extinction. In another case, an impact structure (the Woodleigh structure) in Western Australia seemed to be about the right size and age to have produced the extinction (Mory, 2000a, challenged by Reimold and Koeberl, 2000), but further research revealed that the structure is at least 100 million years too old (Mory, 2000b).
A icy comet, composed in large part (and conveniently!) of isotopically light carbon has also been suggested as a possible cause of the extinction and the carbon isotopic excursion at the Permian-Triassic boundary (Bowring, 1998). However, despite the huge size that such an impactor would have had to have been -- much, much larger than the impactor at the K-T boundary -- all other evidence of this deus ex machina (or rather, saxum -- rock -- ex machina) has disappeared. The suggestion therefore fails a basic test of modern scientific theory: it must be falsifiable, and is not.
The most recent attempt to attribute the end-Permian extinction to an extraterrestrial impact began in early 2001 with the publication of an article in Science. In this article, Luann Becker and her co-authors indicated that their analysis of ratio of Helium-3 (^3He) to the far more common Helium-4 (^4He) isotopes in rocks found at the Permian-Triassic boundary section in Meishan, China revealed evidence of an extraterrestrial impact.
Becker and her colleagues found the anomalous ratios in helium gas trapped within all-carbon spherical structures known as fullerenes, or, more colloquially, as buckyballs. These tiny (molecular size) spheres, which resemble the geodesic domes invented by architect Buckminster Fuller -- hence the names fullerene and buckyball -- are cages which can enclose and entrap gases, and are extremely stable over long periods of time. Fullerenes, presumably of extraterrestrial origin, have even been found in the 1.85 billion-year-old Sudbury impact crater in Canada (Becker, 1994). Thus fullerenes may constitute the ultimate time capsule.
But because fullerenes are nonetheless quite small, they can only enclose tiny quantities of gases, which require extremely careful laboratory techniques to extract. Terrestrial rocks tend to have low ^3He to ^4He ratios because the lighter isotope of helium can more easily escape Earth's gravity. Therefore the higher isotopic ratio identified by Becker and her colleagues argues that the host fullerene and its gases had an extraterrestrial origin.
Becker's proposal found support from Kunio Kaiho and his co-workers in an article that appeared in a 2001 issue of Geology. In the rocks of the Meishan, China, Permian-Triassic boundary section, they discovered iron-silicon-nickel (Fe-Si-Ni) grains, which they indicated can only be created in the extremely high temperatures generated by an impact. They also found a significant increase in the lighter isotope of sulfur (in geochemical terms, this is a negative excursion of d^34S). Kaiho and co-workers attributed this sulfur excursion to a massive release of isotopically light sulfur from Earth's mantle (just below the crust, and therefore from 0 to 70 km -- 0 to about 40 miles -- deep), caused when the impactor (they favored one of much greater size than Becker's group) penetrated the crust. This sulfur would have rapidly been oxidized, drawing down atmospheric oxygen and producing widespread and devastating sulfuric acid rain (Kaiho, 2001).
But in September of 2001, Becker's results were challenged in a letter to Science by Kenneth Farley and Sujoy Mukhopadhyay of the California Institute of Technology. Farley and Mukhopadhyay found no fullerenes in the Meishan PTB section rock specimens they sampled. Lacking fullerenes that they could put a test, the Cal Tech researchers used whole rock samples. In other words, they used ground-up specimens of whole rocks (rather than their alleged constituent fullerenes) to test for the purported helium anomaly. In these specimens, the ^3He concentrations they obtained were significantly more depleted (lower in ^3He, by a factor of from 45 to 150 times lower) than Becker and her associates had found in the fullerenes. Unable to locate any 3He-containing fullerenes, Farley and Mukhopadhyay concluded that there was no evidence for an impact such as had been reported by Becker and co-authors (Farley and Mukhopadhyay, 2001).
Becker and her co-author Poreda responded that the analytic procedures employed by Farley and Mukhopadhyay were not the same as they themselves had used, nor were Farley and Mukhopadhyay's specimens from the exact same site as the material they had analyzed. Further, according to Becker and Poreda, by using bulk rock rather than fullerenes, Farley and Mukhopadhyay had contaminated their analysis. Becker and Poreda indicated that they had re-run their experiments, confirming their results, and stated that they were submitting samples to two independent labs for further examination (Becker and Poreda, 2001).
Eager to learn the results from the independent laboratory analyses, I carefully watched the Technical Comment section of Science for many ensuing months. Nothing appeared. At last I tried to contact Becker via e-mail, but received no response. I presumed this was the consequence of her having been working, within a short period of time, at several different institutions. Some months later, with possibly better e-mail addresses, I tried again, but again received no response. Then I tried contacting Becker's co-author, Poreda, at the University of Rochester. I received no response from Poreda either.
As a last resort, I contacted Ken Farley at Cal Tech, figuring that although he was in no way responsible for the independent analyses promised by Becker and Poreda, he might know when those results might be published. The reply I received was short and to the point: "I have no idea. I wouldn't hold my breath if I were you."
I am no longer expecting either a response from Becker or Poreda, or that any report on the independent analyses will appear in Science.
(Postscript: In the fall of 2003 and spring of 2004, papers were published in Science that indicated further evidence for an end-Permian impact [Basu, 2003; Becker, 2004]. Among these papers' authors were Becker and Poreda. A review of the 2003 paper was published simultaneously in Science by Richard Kerr. According to Kerr, no one except Becker and Poreda has been able to find fullerenes in meteorites. It seems reasonable to conclude, therefore, that neither of the two labs to which Becker and Poreda sent their specimens for independent confirmation did in fact confirm their results.)
2. Volcanism
The second theory regarding the cause of the end-Permian catastrophe is the volcanism theory. Unlike the impactor theory, the volcanism theory starts with extraordinarily good evidence.
There are five leading theories that attempt to explain what happened at the end of the Permian. There are numerous other theories (such as global cooling; see Stanley, 1987) and "sub-theories," which modify the main theories. But the main theories are those which have attracted the most attention from scientists. These are: 1. the impactor (bolide) theory, 2. the volcanism theory, 3. the regression theory, 4. the oceanic overturn theory, and 5. the methane catastrophe theory.
1. Impactor
The impactor theory is, of course, inspired by the success of the Alvarez's explanation for the end-Cretaceous catastrophe. Clearly the impact from this asteroid or comet caused an extraordinary catastrophe for many organisms. Obviously, according to impactor advocates, an even larger impactor would have the energy to do even greater damage to the biosphere. With many large objects (both asteroids and comets) meandering around and through the inner solar system, there are plenty of potential impactors. Consequently, the impactor theory has had a strong appeal and needs to be examined seriously.
The problem with the impactor proposal, however, is that there has been no evidence to support it. There is no iridium layer, as found at the Cretaceous-Tertiary boundary. There is no accepted evidence for shocked quartz, though some have claimed to have found such, but the quality of their specimens has been unconvincing. There are no microtektites -- or the clay spherules which the microtektites by now would have weathered into. (Spherules from the Emeishan volcanic episode [258 to 254 million years ago; Xu, 2004] in the South China area have been found, but obviously these have nothing to do with any alleged impact.) There are no tsunami deposits that record a great impact in the ocean. No impact crater has been located.
Unfortunately, the theory's strong appeal has led some to believe that there is -- or must be -- evidence. One geological chart actually indicates the size of the impactor that the chart's designers (without evidence) knew must have caused the end-Permian extinction. In another case, an impact structure (the Woodleigh structure) in Western Australia seemed to be about the right size and age to have produced the extinction (Mory, 2000a, challenged by Reimold and Koeberl, 2000), but further research revealed that the structure is at least 100 million years too old (Mory, 2000b).
A icy comet, composed in large part (and conveniently!) of isotopically light carbon has also been suggested as a possible cause of the extinction and the carbon isotopic excursion at the Permian-Triassic boundary (Bowring, 1998). However, despite the huge size that such an impactor would have had to have been -- much, much larger than the impactor at the K-T boundary -- all other evidence of this deus ex machina (or rather, saxum -- rock -- ex machina) has disappeared. The suggestion therefore fails a basic test of modern scientific theory: it must be falsifiable, and is not.
The most recent attempt to attribute the end-Permian extinction to an extraterrestrial impact began in early 2001 with the publication of an article in Science. In this article, Luann Becker and her co-authors indicated that their analysis of ratio of Helium-3 (^3He) to the far more common Helium-4 (^4He) isotopes in rocks found at the Permian-Triassic boundary section in Meishan, China revealed evidence of an extraterrestrial impact.
Becker and her colleagues found the anomalous ratios in helium gas trapped within all-carbon spherical structures known as fullerenes, or, more colloquially, as buckyballs. These tiny (molecular size) spheres, which resemble the geodesic domes invented by architect Buckminster Fuller -- hence the names fullerene and buckyball -- are cages which can enclose and entrap gases, and are extremely stable over long periods of time. Fullerenes, presumably of extraterrestrial origin, have even been found in the 1.85 billion-year-old Sudbury impact crater in Canada (Becker, 1994). Thus fullerenes may constitute the ultimate time capsule.
But because fullerenes are nonetheless quite small, they can only enclose tiny quantities of gases, which require extremely careful laboratory techniques to extract. Terrestrial rocks tend to have low ^3He to ^4He ratios because the lighter isotope of helium can more easily escape Earth's gravity. Therefore the higher isotopic ratio identified by Becker and her colleagues argues that the host fullerene and its gases had an extraterrestrial origin.
Becker's proposal found support from Kunio Kaiho and his co-workers in an article that appeared in a 2001 issue of Geology. In the rocks of the Meishan, China, Permian-Triassic boundary section, they discovered iron-silicon-nickel (Fe-Si-Ni) grains, which they indicated can only be created in the extremely high temperatures generated by an impact. They also found a significant increase in the lighter isotope of sulfur (in geochemical terms, this is a negative excursion of d^34S). Kaiho and co-workers attributed this sulfur excursion to a massive release of isotopically light sulfur from Earth's mantle (just below the crust, and therefore from 0 to 70 km -- 0 to about 40 miles -- deep), caused when the impactor (they favored one of much greater size than Becker's group) penetrated the crust. This sulfur would have rapidly been oxidized, drawing down atmospheric oxygen and producing widespread and devastating sulfuric acid rain (Kaiho, 2001).
But in September of 2001, Becker's results were challenged in a letter to Science by Kenneth Farley and Sujoy Mukhopadhyay of the California Institute of Technology. Farley and Mukhopadhyay found no fullerenes in the Meishan PTB section rock specimens they sampled. Lacking fullerenes that they could put a test, the Cal Tech researchers used whole rock samples. In other words, they used ground-up specimens of whole rocks (rather than their alleged constituent fullerenes) to test for the purported helium anomaly. In these specimens, the ^3He concentrations they obtained were significantly more depleted (lower in ^3He, by a factor of from 45 to 150 times lower) than Becker and her associates had found in the fullerenes. Unable to locate any 3He-containing fullerenes, Farley and Mukhopadhyay concluded that there was no evidence for an impact such as had been reported by Becker and co-authors (Farley and Mukhopadhyay, 2001).
Becker and her co-author Poreda responded that the analytic procedures employed by Farley and Mukhopadhyay were not the same as they themselves had used, nor were Farley and Mukhopadhyay's specimens from the exact same site as the material they had analyzed. Further, according to Becker and Poreda, by using bulk rock rather than fullerenes, Farley and Mukhopadhyay had contaminated their analysis. Becker and Poreda indicated that they had re-run their experiments, confirming their results, and stated that they were submitting samples to two independent labs for further examination (Becker and Poreda, 2001).
Eager to learn the results from the independent laboratory analyses, I carefully watched the Technical Comment section of Science for many ensuing months. Nothing appeared. At last I tried to contact Becker via e-mail, but received no response. I presumed this was the consequence of her having been working, within a short period of time, at several different institutions. Some months later, with possibly better e-mail addresses, I tried again, but again received no response. Then I tried contacting Becker's co-author, Poreda, at the University of Rochester. I received no response from Poreda either.
As a last resort, I contacted Ken Farley at Cal Tech, figuring that although he was in no way responsible for the independent analyses promised by Becker and Poreda, he might know when those results might be published. The reply I received was short and to the point: "I have no idea. I wouldn't hold my breath if I were you."
I am no longer expecting either a response from Becker or Poreda, or that any report on the independent analyses will appear in Science.
(Postscript: In the fall of 2003 and spring of 2004, papers were published in Science that indicated further evidence for an end-Permian impact [Basu, 2003; Becker, 2004]. Among these papers' authors were Becker and Poreda. A review of the 2003 paper was published simultaneously in Science by Richard Kerr. According to Kerr, no one except Becker and Poreda has been able to find fullerenes in meteorites. It seems reasonable to conclude, therefore, that neither of the two labs to which Becker and Poreda sent their specimens for independent confirmation did in fact confirm their results.)
2. Volcanism
The second theory regarding the cause of the end-Permian catastrophe is the volcanism theory. Unlike the impactor theory, the volcanism theory starts with extraordinarily good evidence.
science.nasa.gov/science-news/science-at-nasa/2002/28jan_extinction
January 28, 2002: It was almost the perfect crime.
Some perpetrator -- or perpetrators -- committed murder on a scale unequaled in the history of the world. They left few clues to their identity, and they buried all the evidence under layers and layers of earth.
The case has gone unsolved for years -- 250 million years, that is.
But now the pieces are starting to come together, thanks to a team of NASA-funded sleuths who have found the "fingerprints" of the villain, or at least of one of the accomplices
- - -
The terrible event had been lost in the amnesia of time for eons. It was only recently that paleontologists, like hikers stumbling upon an unmarked grave in the woods, noticed a startling pattern in the fossil record: Below a certain point in the accumulated layers of earth, the rock shows signs of an ancient world teeming with life. In more recent layers just above that point, signs of life all but vanish.
- - -
Many paleontologists have been skeptical of the theory that an asteroid caused the extinction. Early studies of the fossil record suggested that the die-out happened gradually over millions of years -- not suddenly like an impact event. But as their methods for dating the disappearance of species has improved, estimates of its duration have shrunk from millions of years to between 8,000 and 100,000 years. That's a blink of the eye in geological terms.
"I think paleontologists are now coming full circle and leading the way, saying that the extinction was extremely abrupt," Becker notes. "Life vanished quickly on the scale of geologic time, and it takes something catastrophic to do that."
Such evidence is merely circumstantial -- it doesn't actually prove anything. Becker's evidence, however, is more direct and persuasive:
Deep inside Permian-Triassic rocks, Becker's team found soccer ball-shaped molecules called "fullerenes" (or "buckyballs") with traces of helium and argon gas trapped inside. The fullerenes held an unusual number of 3He and 36Ar atoms -- isotopes that are more common in space than on Earth. Something, like a comet or an asteroid, must have brought the fullerenes to our planet.
Above: The carbon atoms in a fullerene molecule are arranged in a spherical pattern similar to a geodesic dome. (Geodesic domes were invented by Buckminster Fuller, hence the name of the molecules.) This shape allows the fullerenes to trap gases inside. Image courtesy Luann Becker.
Becker's team had previously found such gas-bearing buckyballs in rock layers associated with two known impact events: the 65 million-year-old Cretaceous-Tertiary impact and the 1.8 billion-year-old Sudbury impact crater in Ontario, Canada. They also found fullerenes containing similar gases in some meteorites. Taken together, these clues make a compelling case that a space rock struck the Earth at the time of the Great Dying.
Some perpetrator -- or perpetrators -- committed murder on a scale unequaled in the history of the world. They left few clues to their identity, and they buried all the evidence under layers and layers of earth.
The case has gone unsolved for years -- 250 million years, that is.
But now the pieces are starting to come together, thanks to a team of NASA-funded sleuths who have found the "fingerprints" of the villain, or at least of one of the accomplices
- - -
The terrible event had been lost in the amnesia of time for eons. It was only recently that paleontologists, like hikers stumbling upon an unmarked grave in the woods, noticed a startling pattern in the fossil record: Below a certain point in the accumulated layers of earth, the rock shows signs of an ancient world teeming with life. In more recent layers just above that point, signs of life all but vanish.
- - -
Many paleontologists have been skeptical of the theory that an asteroid caused the extinction. Early studies of the fossil record suggested that the die-out happened gradually over millions of years -- not suddenly like an impact event. But as their methods for dating the disappearance of species has improved, estimates of its duration have shrunk from millions of years to between 8,000 and 100,000 years. That's a blink of the eye in geological terms.
"I think paleontologists are now coming full circle and leading the way, saying that the extinction was extremely abrupt," Becker notes. "Life vanished quickly on the scale of geologic time, and it takes something catastrophic to do that."
Such evidence is merely circumstantial -- it doesn't actually prove anything. Becker's evidence, however, is more direct and persuasive:
Deep inside Permian-Triassic rocks, Becker's team found soccer ball-shaped molecules called "fullerenes" (or "buckyballs") with traces of helium and argon gas trapped inside. The fullerenes held an unusual number of 3He and 36Ar atoms -- isotopes that are more common in space than on Earth. Something, like a comet or an asteroid, must have brought the fullerenes to our planet.
Above: The carbon atoms in a fullerene molecule are arranged in a spherical pattern similar to a geodesic dome. (Geodesic domes were invented by Buckminster Fuller, hence the name of the molecules.) This shape allows the fullerenes to trap gases inside. Image courtesy Luann Becker.
Becker's team had previously found such gas-bearing buckyballs in rock layers associated with two known impact events: the 65 million-year-old Cretaceous-Tertiary impact and the 1.8 billion-year-old Sudbury impact crater in Ontario, Canada. They also found fullerenes containing similar gases in some meteorites. Taken together, these clues make a compelling case that a space rock struck the Earth at the time of the Great Dying.
Above: What the world looked like 250 million years ago. Image credit: Chris Scotese. [more]
World geography was also changing then. Plate tectonics pushed the continents together to form the super-continent Pangea and the super-ocean Panthalassa. Weather patterns and ocean currents shifted, many coastlines and their shallow marine ecosystems vanished, sea levels dropped.
"If life suddenly has all these different things happen to it," Becker says, "and then you slam it with a rock the size of Mt. Everest -- boy! That's just really bad luck."
"If life suddenly has all these different things happen to it," Becker says, "and then you slam it with a rock the size of Mt. Everest -- boy! That's just really bad luck."
