by Fred Bervoets
Impact craters and mass-extinction
 

The transition from the Paleozoic to the Mesozoic, the Permian-Triassic boundary, is marked by the most severe extinction in the history of life when over 90 percent of all marine species and 70 percent of land vertebrates perished. The P/T extinction is a more dramatic but less heavily published mass-extinction than that of the K/Pg boundary.

Many fossils below the boundary such as trilobites, which once numbered more than 15,000 species, diminish sharply close to the boundary and are not found above it. There also is strong evidence suggesting the extinction happened very rapidly, on the order of 8,000 to 100,000 years. The extinction marked the end of an era, it was the end of the first great pulse of life but it was also the dawn of the \"Age of Reptiles\". But the P/T mass-extinction, also left us with the greatest murder mystery ever, because the \"murderer\" is still at large

Recent analysis of South African rocks reveals that rivers suddenly became clogged with sediments 251 million years ago, indicating the impact stripped of many rooted plants, triggering severe erosion. A global die-off of land plants is also supported by studies that found abrupt changes from meandering to braided river deposits during Permian-Triassic time in Australia, Antarctica and Northern Europe. According to one of the scientist the rocks indicate the rivers changed from meandering to braided within 50,000 years, then returned to normal meandering courses in another 50,000 to 100,000 years.

Mass-extinctions like this P/T extinction and the K/Pg extinction that whipped out the dinosaurs aren\'t rare, other known mass-extinctions are the Cambrian/ Ordovician, Denovian/ Mississippian and the Triassic/Jurassic mass-extinction. Until now the K/Pg extinction was the only one that could possible be triggered by an impact by an Extra Terrestrial Object, (ETO) however scientist have discovered new evidence that Earth\'s most severe mass extinction the P/T extinction was possible also triggered by a collision with a comet or asteroid. Scientist think that the collision wasn\'t directly responsible for the extinction but rather triggered a series of events, such as massive volcanism, and changes in ocean oxygen, sea level and climate. All those \"rapid\" changes possible led to species extinction on a wholesale level. They think so because to kill 90 percent of organisms they had to be attacked on more than one front.

Coincident with the P/T mass-extinction event, the various continents of the Late Paleozoic world, which had up till then been separate and drifting across the oceans, drifted towards one another and in the Late Permian fused together to form the one supercontinent Pangaea. This would have great effects on the ecosystems. The fusion of continental shelves would have reduced species diversity because there would be competition between previously isolated species. As a result of the forming of Pangaea sealevels may have dropped more than 60 meter. The effect of a drop in sea-level may have been catastrophic.

The major problem to the impact hypothese is that the scientist couldn\'t locate the impactsite, however the space body left his tracks in complex carbon molecules called buckminster-fullerenes, or Buckyballs, with the noble gases helium and argon trapped inside the caged structure. Fullerenes, which contain at least 60 carbon atoms and have a structure resembling a soccer ball or a geodesic dome, are named for Buckminster Fuller, inventor of the geodesic dome.

The researchers know these particular Buckyballs are extraterrestrial because the noble gases trapped inside have an unusual ratio of isotopes, atoms whose nuclei have the same number of protons but different numbers of neutrons. Terrestrial helium is mostly helium-4, while extraterrestrial helium is mostly helium-3.

Only trough the extreme temperatures and gas pressures in carbon stars extraterrestrial noble gases could be forced inside a fullerene.

These gas-laden fullerenes were formed outside the Solar System, and their concentration in the sedimentary layer at the boundary of the Permian and Triassic periods means they were delivered by comets or asteroids.

The telltale fullerenes containing helium and argon were extracted from sites where the Permian-Triassic boundary layer had been exposed in Japan, China and less strong in Hungary.

During the time of the supposed impact all Earth\'s land formed a supercontinent called Pangea. The scientist eatimate the size of the comet or astroid was about the same size as
the asteroid believed responsible for the K/Pg mass-extinction.

Due to through the planet\'s tectonic processes there are few 250 million-year-old rocks left on Earth, so most rocks of that age have been recycled. The K/Pg mass-extinction bears strong evidence of the element iridium in the sedimentary layer and it was thought that any asteroid or comet collision would leave traces of iridium.

However the concentration of iridium in the sedimentary P/T layer did not nearly have such a concentration. Its however possible that the two space bodies had different compositions. During the end of the Permian Age the so called Siberian-traps originated, these traps are the result of the most extensive volcanic activity ever, this mass-eruption laid down enough lava to cover the entire planet with three meters of rock over a one-million year period.

The combined effects of impact and volcanism are possible necessary to cause such a tremendous extinction. During the K/Pg period extensive volcanic actity created the Deccan-traps in India.

In April 2000, Australian scientists said they found a 120-kilometer wide crater in western Australia that might be from an impact that caused the Permian-Triassic mass-extinction however, the age of that crater is so poorly known that it is impossible to tie that impact to it.

The impactcrater that possible triggered the K/Pg extinction had a diameter of 180 to 300 meter the mysterious P/T trigger should have been at least the same size. This is an overview of known mass-extinctions and impacts that are dated around the same time

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