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Scientists uncover causes of mass extinction in the ashes
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Posted:September 18, 2012Comments:Views:7
Scientists Uncover Causes of Mass Extinction in the Ashes By TANG YUANKAI DRAGONFLIES as big as a man hover overhead in the oxygen-richatmosphere and mammal-like reptiles called pelycosaurs roam theland, some of them reaching up to six meters in length. Underwater,we find coral reefs [link widoczny dla zalogowanych] of rugosa, also known as horn coral for itsoften remarkable resemblance to rhino horns, and honeycomb-liketabulate corals. These exotic scenes are some that you might [link widoczny dla zalogowanych] haveseen during the Permian Period, which existed around 295 milion to250 million years ago. But at the end of this period, a massextinction occurred resulting in 95 percent of all marine speciesand 75 percent of all land species being wiped out. Scientists including Chinese paleontologists have madebreakthroughs in determining the timing of the Permian-Triassicmass extinction, and come closer to finding its cause.
Since theappearance of organisms on earth 3.8 billion years ago, at leastfive [link widoczny dla zalogowanych] mass extinctions have occurred. But that at the end of thePermian Period was the most devastating. Shen Shuzhong took the lead in the research that involved more than20 specialists from the Nanjing Institute of Geology andPaleontology, Chinese Academy of Sciences (NIGPAS), theMassachusetts Institute of Technology (MIT), [link widoczny dla zalogowanych] the American NationalMuseum of Natural History and several other research [link widoczny dla zalogowanych] institutes.Their 10-year research overturned previous estimates by Chicagoexperts in 1984 of the mass extinction lasting 10 million years,coming up with the new figure of just 200,000 years, about 252.28million years ago. Shen Shuzhong and his research team traveled to 20 strata boundarysections in southern China, Tibet, Pakistan and Kashmir to collectthe fossils needed for analysis.
They found particularly largedeposits of volcanic ash in Meishan in Zhejiang Province, theworld s most famous record of the Permian-Triassic massextinction, and Guangyuan in Sichuan Province. These and othersamples were analyzed at MIT, where scientists employed the mostadvanced dating methods. The paper announcing their results, produced by Chinese scientistsin conjunction with 14 scientific research institutes, waspublished in the authoritative U.S. Science magazine.
Shen Shuzhongcommented, The mass extinction had been studied for decades, yetthe timing and duration of the extinction and recoveries were notpinpointed. The significance of this breakthrough is that a more accurate timescale for the extinction and the recovery that followed will helpscientists further understand the physical, ecological, andchemical changes that occurred during the event, and to testpossible causes. Research also found evidence of the causes of the extinction usinga computerized ratio optimization method, information collectedfrom the 29 volcanic ash beds and a database of 1,450 types offossils from the period. Previous theories include that published in Science magazine in2000 by world-renowned Chinese paleontologist Jin Yugan, whopostulated that an instantaneous event led to the mass extinction.Some American and Japanese scientists presume that intensiveseismic waves from the collision between asteroids and the earthexterminated almost all species within a span of thousands ofsquare kilometers. This view remained [link widoczny dla zalogowanych] popular for a time.
The scientists involved in the recent research, however, believethat the massive volcanic eruptions and the release of methane fromthe surface of the earth led to increased amounts of carbon dioxidein the atmosphere that intensified the greenhouse effect. Shortageof oxygen [link widoczny dla zalogowanych] in the sea led to the mass extinction of marine species.Meanwhile rapid global warming and aridity gave rise to frequentlarge-scale forest fires that were disastrous for the tropicalforests in equatorial regions. They led to further aridity and spedup the collapse of the soil system. These events completely changed the appearance of the world ssurface. If there had been no such mass extinction during thePermian Period, people would have seen two-meter-long dragonfliesin real life, Shen said with a sigh.
Paleobotanist Wang Jun, a colleague of Shen Shuzhong, revealed thatfew fossils of living things from right after the mass extinctionwere found. The [link widoczny dla zalogowanych] recovery of life on the earth took more than fivemillion years, significantly longer than after any other massextinction, said Wang. Fortunately a few marine and terrestrialspecies survived. Shen said that these remaining species went on topopulate the earth during the Triassic Period and included whatwould soon evolve into one of paleontology s most iconiccreatures, dinosaurs.
Shen Shuzhong sees these findings as an important message fortoday s world. The depraved situation of the earth s surfacehas a [link widoczny dla zalogowanych] long-term impact on the ecosystem. [link widoczny dla zalogowanych] But if it goes beyond theenvironment s capabilities, the ecosystem can [link widoczny dla zalogowanych] collapse in [link widoczny dla zalogowanych] a shorttime, he said. This enlightens our environmental awareness.
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