A Middle Pliocene stage has been suggested as well; I do not remeber the
name immediately, but at any rate the nomenclature is still a bit
unsettled. Zanclian-Piacenzian should do for now, though.
>> The South Pole had been cold for about 30 million years by that point.
> That seems to be controversial. But again, the key point is the onset
>glaciation episodes. Schultz himself, a planetary geologist, indicates
>new Argentinian discovery at 3.3 Ma may be a possible trigger for
I do not know of anyone who accepts conventional geologic dating who would
question an onset of substantial glaciation in Antarctica in the latest
Eocene to early Oligocene. 3.3 is about the right time for increased
northern hemisphere glaciation, but there are other factors at that time
that could cause the glaciation without the added help of a bolide. The
bolide could have helped, although there seems to be uncertainty as to just
what effects it would have.
>> To cause a single crater, there is no need for a planetary explosion.
> Before a few months ago, we knew of zero craters at that epoch. Now we
>of one. By extrapolation, in 50 years we'll know about hundreds. :-)
> The explosion at 3.2-3.3 Ma was of a minor, Moon-sized,
>body. So the effects on Earth were minor compared to the effects of the
>planet explosion at 65 Ma. -|Tom|-
I'm still not clear as to why the mid-Pliocene crater needs an exploding
planet when there are plenty of ordinary asteroids or comets that could do
the job. Also, there are other, bigger impacts on Earth besides the K/T.
Whether there is any evidence for a Permo-Triassic impact is still debated.