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Re: Missing the point of Nemesis
Mr. Bagnall,
The point I was trying to make with my "ramblings" is that the sun could
very well be a multiple sun system, not a lone star, thereby increasing the odds
for extinction periodicity. Nemesis is too small, too far away, and too
unstable an orbit to be causing these 13, 26 and 65 M.Y. extinction periods.
Nemesis was coined by the media to fit the 26 M.Y. cycle seen by R & S.
Randy
Phil Bagnall wrote:
> It is evident from the postings to this list that some people are missing
> the point of the Nemesis hypothesis. There are people rambling on about
> brown dwarfs and multi-sun systems, both of which are totally irrelevant.
>
> The problem is that Raup and Sepkoski claim that mass extinctions are
> cyclical and that, at least since the Permian, the period has been about 26
> million years. If all the extinctions had the same cause - and it is by no
> means clear that they did - then one possibility may be a regular influx of
> comets from the Oort cloud. The Oort cloud lies at a distance of about
> 30,000 to 100,000 AU from the Sun. One of the ways in which the cloud could
> be disturbed would be by the existence of a solar companion star - the
> so-called Nemesis star. But it is dynamically difficult, if not impossible,
> for such an orbit to have become established and to have lasted for the life
> of the Solar System. It has nothing to do with what type of star Nemesis
> is - or how many companion stars there may be - it is purely a dynamical
> problem based on the distance of the Oort cloud.
>
> Now, it has got to be said that Raup & Sepkoski's data have been subject to
> much criticism from statisticians and palaeontologists alike. The geologic
> record is by no means complete, and doubts have been raised about the
> radiometric timescales used by the two researchers. There is also a
> background 20-30 genera extinctions every million years, which serves to
> complicate matters further.
>
> If anyone seriously wishes to tackle this problem then perhaps the approach
> they should take is to look at the history since the dinosaur extinction of
> 65 mya. If R&S are correct, then there should have been mass extinctions 39
> mya and 13 mya. Where is the evidence for these extinctions? Did the Nemesis
> object drift from its unstable orbit at the time of the dinosaur extinction
> thus putting an end to the cyclical nature of extinctions?
>
> A couple of good starting points are the books by Clube and, if you have an
> awful lot of time on your hands, by Sharpton and Ward. There have been
> numerous other books and papers of this subject but the three I have listed
> lay the foundations for research.
>
> References:
>
> Clube, S.V.M. (Ed.) 1989 Catastrophes and Evolution: Astronomical
> Foundations. Cambridge University Press
>
> Raup, D.M. & Sepkoski,J.J. 1984 Periodicity of extinctions in the geologic
> past. Proceedings of the National Academy of Sciences, 81, 801-815
>
> Sharpton, V.L. & Ward, P.D. (Ed.) 1990 Global Catastrophes in Earth History.
> Geological Society of America Special Paper 247.
>
> Phil Bagnall
> www.ticetboo.demon.co.uk
>
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