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Re: Meteroic Evidence For Permian-Triassic Extinction



On Saturday 22 Nov 2003 3:15 am, Phil Hore wrote:

>I'm boning up (exscuse the pun) on the start of the Triassic for a
> peice I'm writting and what I find odd is I'm finding no 'extinction
> of 95%' of all life happening. There is certainly a lot going on and
> many species are disapearing, but 95% just doesn't seem to be the
> figure I'm seeing...maybe more 65-70 %...to be fair I've only just
> started my research so I have a lot more to look through. I just find
> it odd and am thinking that if there was an impact at the end of the
> permian, it was a lot more localised then the global killer of the KT
> impact.

The 95% (96%) figure came from reverse rarifaction graph which Raup 
published in 1979. (Raup D M, Size of the Permo-Triassic bottleneck and 
its evolutionary implications, Science 1979; 206: 217-18). It was 
actually the upper limit with a range of 80-96%. Raup himself later 
wrote in : Extinction: Bad Genes or Bad Luck ?, OUP, 1993, pp 72-74

"Many readers will have heard that 96 percent of all species living near 
the end of the Permian were killed in the big mass extinction at that 
time. This number comes from the reverse rarefaction graph of Figure 
4.2. This estimate is probably an exaggeration, because the extinction 
of species is not completely random. If extinction is focused on 
certain genera and families, killing will be concentrated in these 
groups. If reverse rarefaction is used to estimate species kill from 
the extinction rates of genera or families, any departure from random 
(Field of Bullets) killing will exaggerate species kill.

I am slightly embarrassed by the wide use of the figure of 96 percent 
for the Permian because I was responsible for it in a 1979 article 
presenting the reverse-rarefaction method. Although my article 
contained ample caveats about the random-killing assumption and 
although I said that the 96 percent estimate was an upper limit, all 
too many users of the number have neglected to mention the caveats. In 
truth, I probably did not exert myself to emphasize them."

Most other estimates suggest a 70% extinction for terrestrial & 85-90% 
for marine organisms. See : Alper J, Earth's near-death experience, 
Earth (January) 1994; 3 (1): 42-51

-- 

Gautam Majumdar

Please send e-mails to gmajumdar@freeuk.com