Momo, your post is well thought out and very reasonable.
However, I do not agree with your assesment of the extinnctions we are facing today.
I was talking about mass extinctions. Not species, not even genera, but classes and phylums dying out.
This is not the case today, nor was it in the Pleistocene.
Umm, excuse my ignorance.
I should have written Phyla.
Mj,
Good point, which is precisely the problem. Occam’s Razor doesn’t work here.
There are simply too many good theories going around.
Which is why I don’t think we’ll ever know for sure.
Momo, a nice response. If you’re looking for picky precision, they’re ichthyosaurs and mosasaurs (the latter of which you caught yourself).
I was under the impression that prior to the discovery of Chicxulub, all known astroblemes were either (a) fairly recent small ones such as the one in Arizona, or (b) large ones on geological shields, particularly the Canadian one, which were nearly all Precambrian in date. (There was IIRC one exception which was early Paleozoic.) This is all based on MFM (my faulty memory) so I welcome corrections.
Now, the impacts from this junk are proportional in some large ratio (as the square I think) to the size of the impacting body. If you drop a cobble-size rock or set off a firecracker in Serengeti Park, the animals do not all keel over and die. If, on the other hand, you set off a 50-megaton H-bomb there, there’s a good chance they would. Likewise if you impacted it with a meteor one mile in diameter traveling at escape velocity or greater.
Something that produced a 200-mile-diameter crater in the Yucatan and sent tidal waves up the Gulf Coast and Mississippi Embayment (fossil evidence for this in appropriate formations) would probably produce enough impact energy to have the “desired” (i.e., interpreted) result.
As for dust in the atmosphere, it’s quite capable of holding it for long enough. Stephen Jay Gould reports on the explosion of Tambora in Indonesia in 1815 and attributes the weather of 1816 (“The Year Without a Summer”) to this. Krakatoa, only a fraction the size of Tambora’s explosion, reddened sunsets around the world for over a year after, and the winter of 1888, far colder and snowier than normal, was attributed to its influence by some earth scientists.
Finally, among foraminiferans and other planktonic life, it appears that the survivors were those which were genetically capable of adapting to an extended cold period (e.g., encysting).
And of course I am fully aware that the dinosaurs were not the only things to become extinct. I simply used that as a short, catchy title for the thread. I could have called it “Hieronymus Bosch”… 