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Re: impact extinctions
Stan Friesen wrote:
>Starting about 5 million years before the boundary, oceanic
>isotope curves start to swing wildly. Several show a sharp peak
>in one direction, and then a rapid shift to the opposite extreme
>persisting across the P-Tr boundary. (This is obvious in both the
>Oxygen isotope and Carbon isotope ratios). The Strontium isotope
>ratio shows a rapid, but steady, decline over this interval.
>Finally, at this time there was a major "Ocean Anoxic Event".
>This is where the oxygen compensation depth reduces to a point
>such that most continental shelf areas are under anoxic waters.
>Some workers have even speculated, based on the OAE and the
>rapidly changing oxygen ratios, that the *atmospheric* oxygen
>concentration may have dropped by as much as 50%.
>So, with *three* major sources of stress (oceanic anoxia,
>glaciation, and major volcanism) ocurring at this time,
>what need is there for an additional factor to explain the
If impacts are periodic, and not random, in nature, then it has been proposed
that the mechanism that causes the periodicity (eg. a companion star) sends in
a shower of comets over a period of hundreds of thousands or millions of years.
If that is the case, one might well expect to see a gradual change over this
time period as the frequency of impacts follow some kind of bell curve. Stan
provided no explanation for what caused eg. anoxia, and I am wondering if some
of the effects noted above MIGHT BE CAUSED BY impacts. Large impacts in the
ocean (and, to an extent, on land) would certainly disturb (reorganize)
deposits by digging a crater to throw those older deposits into the air, and
by stirring up the mud and moving older material throughout the sea via tidal
waves or natural ocean currents.
Yes, there may be problems to be solved in the impact hypothesis. The reason I
still support it is that there are even bigger problems with all the
alternatives that I have seen proposed to replace it.