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Re: Hell Creek [VERY LONG]



----- Original Message -----
From: "Allan Edels" <edels@msn.Com>
Sent: Thursday, May 30, 2002 8:37 AM

>     Facts are:
>
> [...]
>     2)    The object hit the earth around 65 mya.

_At_ 65 Ma ago, to be precise, at 64.98 +- 0.05 Ma ago.

>     3)    Lots of things changed on earth around 65 mya - climate, land
> vs. sea ratios, etc.

"Around". I'll ask Rampino next Monday on the last word on those climate
change issues; the (milder than thought for long) regression that's seen in
the Western Interior Seaway may not have been a global phenomenon either,
and cannot have lead to global extinctions in any case.

> 2)    There were a lot of different survivors, including birds,

Hardly any birds.

> crocs,

Not the turtle-eating ones. Someone please find :-> a good record of LK
Notosuchia which aren't known from the Cenozoic.

> mammals,

Suffered quite some losses, though it's for most groups unclear exactly
when. The Asian clade of Eutheria (Zalambdalestidae, *Kennalestes*,
*Ukhaatherium*, maybe Zhelestidae), the deltatheroid, stagodontid and most
or all pediomyid metatherians, the last docodont (*Reigitherium*), the last
triconodontid (*Alticonodon*), maybe a relative of that (*Austroconodon*)
and IIRC some "symmetrodonts" are known from the Campanian and/or
Maastrichtian but not the entire Cenozoic. Only one dryolestoid,
*Peligrotherium*, has so far been found in Paleocene layers. There are
stagodontids and pediomyids in the Hell Creek Fm. Many multituberculates
snuffed it IIRC, but I really know too little about them.

> frogs

Well, they survived Mt. St. Helens, I've read in the archives.

> 3)    Pterosaurs had all disappeared prior to the Maastrictian (possible
> exception - _Quetzalcoatlus_).

Outdated. *Hatzegopteryx* and the Spanish beast are end-Maastrichtian. How
old are *Bennettazhia* and *Montanazhdarcho*?

> 4)    Ichthyosaurs had all disappeared several million years prior to
> K-T.

Not just several Ma, but apparently in the Cenomanian-Turonian catastrophe.
And before that (since the beginning of the K), there was only one genus,
*Platypterygius* (whatever a genus is... don't know how many species have
been described for it).

> 5)    Many of the dinosaurs were in a decline (in terms of numbers of
> genera and species).

Now is this a fact, or is it just the Signor-Lipps effect? (So far what once
was the 3 m gap shrinks every time someone looks more closely.) Is it known
from outside the Hell Creek Fm? (AFAIK not.)

> 7)    The climate changed drastically (geological time) - from very warm
> and humid to much cooler and drier.

Isn't that an old factoid?

> 8)    Foraminifera changed at the K-T, indicating the climate change
> (They went from very complex forms, usually indicative of warm water, to
> very, very simple forms, usually indicative of cold water).

>From a very _diverse_ array of simple and complex forms to a monoculture of
small and simple forms -- a part of the plankton extinction. Strangelove
ocean.

> 9)    The Deccan Traps (of India) had been flowing for several million
> years prior to K-T, and seem to have continued several thousand years
> after it.

Several million years after it IIRC.

>     h)    If the Ozone layer was damaged or removed,

Probably it was. The impact must have created large amounts of nitric oxides
and blasted them far upwards. Should destroy the ozone layer immediately
according to apparently unpublished calculations. :-} BTW, nitrogen dioxide
(and the monoxide becomes dioxide pretty soon) is deeply reddish-brown
[FREEZE], while dinitrogen monoxide = laughing gas is a powerful greenhouse
gas [BAKE]. :-)

> 13)    Amber gas inclusions (air bubbles) indicate a variation in oxygen
> and carbon dioxide levels.

Is amber reliable? I mean, is it reliable to store oxygen in a material that
can burn? Won't that produce more and more carbon dioxide over time and (in
relation) slightly decrease the amount of oxygen?

> Both were at their highest levels during the
> end of the Cretaceous (last 20 my).
>     a)    O2 levels:
> Permian  - 15%,
> Late Jurassic  -  28%,
> Late Cretaceous (Pre-K-T)  - 35%,
>              After K-T  -  28%,
> Mid-Miocene  -  14%,
> Late Eocene - 15%,
> Current Levels - 21%.
>     b)    THERE REMAINS SOME QUESTION AS TO THE VALIDITY OF THESE
> LEVELS.  Some other techniques seem to show the same level as currently
> (i.e. 21%) throughout all these eras.

What I've read in New Scientist 3 or 4 years ago --

Carboniferous: 35 %
then "normal" (around 21)
Middle Jurassic -- Eocene: 28 %
since then: "normal"

In the Paleo- and Eocene, when there neither deserts nor grasslands nor
inland ice (hm... probably I'm oversimplifying), I'd personally expect
higher oxygen levels than today.

> 14)    If large firestorms occurred, due to a large bolide impact, much
> of the atmospheric oxygen would have been converted into carbon dioxide,
> with insufficient vegetation remaining to pump O2 back into the
> atmosphere quickly enough.

But after that, both oxygen and carbon dioxide levels should, I think, have
remained pretty constant for quite some time -- both photosynthesis and
respiration were largely shut off.

> This would have made it impossible for the
> larger animals to survive, because they had evolved to take advantage of
> the higher O2 content.

I don't think so. I mean, many if not all dinosaurs apparently had
bird-style respiration systems. Furthermore, there are very simple things to
do when there's less oxygen in the air -- to breathe more often, and to
boost the production of red blood cells. Both of these methods are
unavailable to insects, and therefore oxygen content seems to limit insect
size. I don't know of any monster K insects, though, while the gigantic
Permian insects are famous (not to mention the Carboniferous
*Arthropleura* -- it also had trachaeae, right?).

> NOTE ALSO: The Signor-Lipps effect. The effect is analogous to the
> Heisenberg Uncertainty Principle - the closer you get to examining your
> subject, the more likely you are to introducing errors, or not noticing
> important info.

Actually not. What it is about is the simple fact that rare fossils are
unlikely to be found in _any_ thin layer, therefore their exact extinction
date -- which must coincide with the deposition of a thin layer -- won't
coincide with their last (known) appearance. Ways to reduce it are to sample
more intensively (gee...) and to sample more sites. Frequently forms that
disappear quite some distance below some boundary in one site last to the
bitter end just a few kilometers away and vice versa (there are published
examples for the K-T and the P-Tr boundaries, ask me for refs for the
latter).

Some more facts...

-- At every mass extinction investigated so far, there's a _sharp_ shift in
the 12C/13C ratio in the (marine) sediments, indicating that photosynthesis
was switched off.
-- The K-T has the famous fern spore spike. The P-Tr has a fungal spore
spike ?instead -- looks like the whole world went moldy. A marine K-T site
in New Jersey has lots of brachiopods instead -- brachiopods had evolved
when there still was hardly any plankton and have the lowest metabolism of
all plankton eaters or something like that; ref: William Gallagher & Luther
Young: Dinosaurs of the East Coast, publisher forgotten, 1995.
-- At the K-T, sedimentation rates dropped _sharply_ at the K-T and remained
down for several thousand years in a site where most of the sediment is
composed of plankton shells. Strangelove ocean again.
-- There's a site in India where the boundary layer lies in an intertrappean
bed. Right up to the boundary there are dinosaur remains, but not above,
showing that at least dinosaur extinction was unconnected to at least the
lava flow pattern in that place.