From Steve Ringwood
Epping, Essex
I read “What really killed the dinosaurs?”
(16 August, p 22) with great
interest, particularly Allen and Yabushita’s proposition of an encounter with a
giant molecular cloud (GMC). I came to a similar conclusion in a paper entitled
“On the origin of change”, submitted 17 years ago to the Journal of the
British Astronomical Association.
In it I showed that by isolating major changes of evolutionary fortune (good
and bad), six predominant periods of development can be derived for the last
half billion years. Of these, three, covering periods from 535 to 500, 310 to
275 and 75 to 60 million years ago, are each separated by approximately 225
million years. Of the remainder, one spanning 390 to 360 million years ago and
one of about 150 million years ago do likewise. Since the Solar System’s
galactic “year” is of this order, the Sun will have been in the same region of
space for each of the two sets of correlations.
Most occasions of marked change in the Earth’s environment could therefore be
explained by its passage through just two GMCs. A third GMC encounter would be
required for the remaining period, occurring between 195 and 240 million years
ago, but either there was no previous encounter (about 442 million years ago)
with this particular GMC, or fossil evidence for a change at that time is
minimal. Intriguingly, by continuing with the 225 million years’ periodicity, we
would be within this third cloud right now—and one wonders if humanity’s
effect on the extinction rate is masking a “natural” one.
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Though opinions may differ regarding the exact timing of specific events,
there can be no doubt that on the large scale they do coincide spatially. Of
course, by knowing the Sun’s galactic orbital rate, together with the
approximate timings of evolutionary events, it is possible to estimate the
extent and position of these GMCs. I calculate that one cloud should lie between
galactic longitudes 20° and 50°. Perhaps someone may care to look.
Of course, the weakness in trying this sort of geo-astronomical correlation
is the error margins involved in attempting to date evolutionary events (whose
resolution is measured by palaeontologists in sediments, rather than millions of
years). Until better techniques are developed, the error bars can be modified to
fit many theories, especially in a problem crossing two disciplines.
