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

Re: impact - LONG

Allen Edels wrote a rather long list which nicely summarized the KT
extinction event; I'm only responding to a few

>5)    Many of the dinosaurs were in a decline (in terms of numbers of genera
>and species).  (They may have been approaching another minor extinction
>event, which they had recovered from in the past).

As Tracy said, the reality of the 'decline' is in dispute.
>6)    All the mega-fauna disappeared.  (i.e. All the large animals
>disappeared - including the large crocs).  I believe the largest surviving
>land animals were less than 30 Kg.  (Sea-going animals may have been
>slightly larger).

I've seen estimates that the largest animals surviving the KT were only 5
kg. Regardless of the exactly threshold, I consider this one of the most
important datums on the event. If only we knew what it meant.

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

Everything I've seen makes me consider oxygen levels derived from amber
highly suspect. On the other hand, it's hard to imagine that oxygen levels
would have remained constant at current levels for hundreds of millions of
years. Oxygen levels may be a variable that we can't reconstruct.

>14)    If large firestorms occured, due to a large bolide impact, much of
>the atmospheric oxygen would have been coverted into carbon dioxide, with
>insufficient vegetation remaining to pump O2 back into the atmosphere
>quickly enough.  This would have made it impossible for the larger animals
>to survive, because they had evolved to take advantage of the higher O2

According to the Handbook of Chemistry and Physics, the atmosphere contains
approximately 10E15 tons of oxygen, but I couldn't find a number for the
mass of the biosphere. If you had incomplete burning of biomass, it could
have yielded a suffocating brew of toxins such as carbon monoxide and
hydrocarbons long before it consumed a significant fraction of oxygen.

-- Jeff Hecht