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Missing the point of Nemesis

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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