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Re: the cause(s) of MASS extinction



>1)  "Dinosaurs were always fluctuating in diversity and were already in
>decline at this time." - Before we can talk about what caused this mass
>extinction, we have to AGREE that it was a mass extinction, which is to
>say, we have to agree that it is something EXCEPTIONAL and not an
>everymillienum, run-of-the-mill event.  Once we agree on this point,
>presumably we can argue about whether this exceptional event has
>exceptional CAUSE(S).
>

On thise and other related issues, there is one topic I've not seen 
addressed.  Astronomers have postulated that a solar companion with 
a large period may cause cometary material to be thrown into the 
inner solar system.  This would cause impacts roughly corresponding 
to the periodic extinctions we observe.  What doesn't seem to be 
addressed is that this would likely lead to multiple impacts over a 
short (geologically speaking) time span. A gradual disappearance of 
the dinosaurs could still be attributed to earlier impacts resulting 
from the same source.  It was also previously noted, that only about 
1/4 of the impacts will hit land, so for any land hit, we could expect 
three ocean hits.  Nor does this address that other land hits may 
still be missed.