[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: ? re: Asteriod/Comet impact at K-T Boundary



 >
 >From everything I have read and heard there seems to be little doubt
 > that something large impacted the earth 65 mya. I do have doubts
 > though, that this caused the demise of the dinosaur and other life
 > forms at the time. My question is why is the Iridium layer deposited
 > almost a meter above the last of the dinosaur fossils.

It isn't any longer.  There are now known isolated dinosaur bones
only a few inches below the Iridium anomoly.

However, the *abundance* of dinosaur remains drops precipitously
about 2-3 meters below the boundary clay.  Also, some dinosaur
teeth have been found in stream beds that apparently post-date
the Iridium layer.  (Only apparently because stream beds are,
in part, erosional, so determining their time layer can be
difficult). This may no be significant however, as teeth are
easily reowrked, so they may have been redeposited from slightly
older clays.

 > I have never seen this issue addressed. This meter
 > would seem to account for a gap of 2 million plus years between the
 last
 > dinosaur fossils and the impact.

No, it is more like 100,000 years, at least in the Lance/Hell
Creek Formations.

 > I have read that the dust and soot from
 > fires caused by the impact would remain in the air for only few
 years at most
 > before settling back to earth. It would seem to me that the last of
 the
 > Dinosaur fossils would be right at the iridium layer or even on top
 of it,
 > not a meter beneath.

Yep, in an impact caused extinction, the dinosaur fossils shouldn't
be starting to drop out *before* the impact.

I posted a reference discussing this very issue last week sometime.
Here it is again:

        Williams, 1994,
        "Catastrophic versus non-catastrophic extinction
        of the dinosaurs ..."
        Journal of Paleontology, vol 68, nbr 2.

 > extinction. Why did other species survive:
 > Birds, Crocadiles, snakes,turtles, lizards, mammals,sharks etc.
 etc.and most
 > species of plant life? I understand that almost all plant life came
 through
 > the K-T boundary, but in different proportions.

Yep, though apparently, at least in North America, the forests
were temporarily removed, since immediately above the Iridium
layer almost all "pollen" is fern spores (for about a centimeter).

The basic pattern of the extinction was the same as most others:
larege and/or specialized land animals got chopped.  Small, mostly
generalized land animals made it through.  In the sea the pattern
was similar. except that most planktonic forms (microscopic) also
died out as well.

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.