How to kill 95% of all life?
Monday, 24. March 2008, 17:54:42
The debate is still going on about what lead to the mass extinction 251 million years ago - the end of Permian. According to the media “British researchers, reporting on Sunday in the journal Nature Geoscience, ruled out a leading theory that the oceans became starved of oxygen and rich with sulphide, causing marine life to die out.” I have not read the report in Nature Geoscience, and the short notes in TerraDaily and PhysOrg seem a bit vague, and even confusing, but the team of scientists apparently used a two-dimensional computer model of atmospheric chemistry to test the theory. I take it, however, that the theory in question was more or less the following.
A severe anoxic event at the end of the Permian could have made sulphate-reducing bacteria the dominant force in oceanic ecosystems, causing massive emissions of hydrogen sulphide (a stinking gas best known for its rotten egg smell) which poisoned plant and animal life on both land and sea, as well as severely weakening the ozone layer, exposing much of the life that remained to fatal levels of ultraviolet radiation. See Kump et al. 2005. This theory has the advantage of explaining the mass extinction of plants, which ought otherwise to have thrived in an atmosphere with a high level of carbon dioxide. Fossil spores from the end of Permian further support the theory: many show deformities that could have been caused by ultraviolet radiation, which would have been more intense after hydrogen sulphide emissions weakened the ozone layer.
A range of killing scenarios have indeed been discussed over the past 20 years or more. Apart from oceanic anoxia, we have heard about major continental plate movements, sea level changes, salinity changes, pH changes, global warming (as of late), and the two prime suspects: asteroid impact (in Antarctica ?) or mass volcanism (the Siberian traps), or maybe a combination of some of these events.
Whatever the culprit, it is still an intriguing question. A good review on large igneous provinces and mass extinctions, by Wignall, was brought by Earth Science Reviews in March 2001, unfortunately not with free access.
Benton & Twitchett wrote a good review “How to kill (almost) all life: the end-Permian extinction event” in Trends in Ecology & Evolution of 18 July 2003. A reprint of this paper can be downloaded as pdf file by clicking here. This paper contains the essence of the book “When Life Nearly Died. The greatest mass extinction of all time”. Michael J Benton, Thames & Hudson, 2003.
There may be some confusion over whether certain geochemical signatures at the Permo-Triassic boundary represent causes or effects of the extinction.
One suggestion for a scenario combining different processes is: the impact of an extraterrestrial body (like an asteroide) could have caused sudden mass mortality of organisms in sea and on land. The accompanying pressure wave could have triggered both the release of methane from hydrates stored on the bottom of the oceans and the
initiation of Siberian volcanism. After the initial events of the first 10,000–30,000 years, the reduction of land plant productivity lasted for millions of years, leading to a drop in global organic carbon burial and a shift of the major site of burial from the terrestrial to the marine environments. This would help to explain the very low level of Triassic coal deposition as compared with that during the Permian. Initial increased organic burial in the marine environment, caused by the sudden input of dead organisms, led to a higher frequency of basins with anaerobic conditions and a greater burial of sedimentary pyrite in the early Triassic. A suggestion out of many.
Maybe the flood basalt is temporarily on the winning hand, but undoubtedly the debate will go on for a long time to come.
Recent media story:
• http://www.terradaily.com/reports/Stinking_seas_not_to_blame_for_mother_of_all_mass_extinctions_999.html
• http://www.physorg.com/news125509388.html
Other (older) references:
• http://www.pnas.org/cgi/content/full/99/7/4172?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=Berner&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT
• http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V62-42HFR73-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=400a45eff6acca36ec2f140df0fd425d
• http://www.gsajournals.org/perlserv/?request=get-abstract&doi=10.1130%2FG21295.1
A severe anoxic event at the end of the Permian could have made sulphate-reducing bacteria the dominant force in oceanic ecosystems, causing massive emissions of hydrogen sulphide (a stinking gas best known for its rotten egg smell) which poisoned plant and animal life on both land and sea, as well as severely weakening the ozone layer, exposing much of the life that remained to fatal levels of ultraviolet radiation. See Kump et al. 2005. This theory has the advantage of explaining the mass extinction of plants, which ought otherwise to have thrived in an atmosphere with a high level of carbon dioxide. Fossil spores from the end of Permian further support the theory: many show deformities that could have been caused by ultraviolet radiation, which would have been more intense after hydrogen sulphide emissions weakened the ozone layer.
A range of killing scenarios have indeed been discussed over the past 20 years or more. Apart from oceanic anoxia, we have heard about major continental plate movements, sea level changes, salinity changes, pH changes, global warming (as of late), and the two prime suspects: asteroid impact (in Antarctica ?) or mass volcanism (the Siberian traps), or maybe a combination of some of these events.
Whatever the culprit, it is still an intriguing question. A good review on large igneous provinces and mass extinctions, by Wignall, was brought by Earth Science Reviews in March 2001, unfortunately not with free access.
Benton & Twitchett wrote a good review “How to kill (almost) all life: the end-Permian extinction event” in Trends in Ecology & Evolution of 18 July 2003. A reprint of this paper can be downloaded as pdf file by clicking here. This paper contains the essence of the book “When Life Nearly Died. The greatest mass extinction of all time”. Michael J Benton, Thames & Hudson, 2003.
There may be some confusion over whether certain geochemical signatures at the Permo-Triassic boundary represent causes or effects of the extinction.
One suggestion for a scenario combining different processes is: the impact of an extraterrestrial body (like an asteroide) could have caused sudden mass mortality of organisms in sea and on land. The accompanying pressure wave could have triggered both the release of methane from hydrates stored on the bottom of the oceans and the
initiation of Siberian volcanism. After the initial events of the first 10,000–30,000 years, the reduction of land plant productivity lasted for millions of years, leading to a drop in global organic carbon burial and a shift of the major site of burial from the terrestrial to the marine environments. This would help to explain the very low level of Triassic coal deposition as compared with that during the Permian. Initial increased organic burial in the marine environment, caused by the sudden input of dead organisms, led to a higher frequency of basins with anaerobic conditions and a greater burial of sedimentary pyrite in the early Triassic. A suggestion out of many.
Maybe the flood basalt is temporarily on the winning hand, but undoubtedly the debate will go on for a long time to come.
Recent media story:
• http://www.terradaily.com/reports/Stinking_seas_not_to_blame_for_mother_of_all_mass_extinctions_999.html
• http://www.physorg.com/news125509388.html
Other (older) references:
• http://www.pnas.org/cgi/content/full/99/7/4172?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=Berner&searchid=1&FIRSTINDEX=0&resourcetype=HWCIT
• http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V62-42HFR73-1&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=400a45eff6acca36ec2f140df0fd425d
• http://www.gsajournals.org/perlserv/?request=get-abstract&doi=10.1130%2FG21295.1
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