Re: More Than Meteor Killed The Dinos

[Tommy Tyrberg <tommy.tyrberg@norrkoping.mail.telia.com>]

At 04:32 2006-10-25, Deinonychus47@aol.com wrote:
> To all:
>
> Based upon the stream of comet impacts on Jupiter, could not a pair of  large
> meteorites or comet fragments) have impacted the Yucatan at the end  of the
> Cretaceous Period and the evidence for what would have been the  first crater
> been obliterated by the close-behind second object? If a comet, it  could 
> have
> been torn apart by the gravity of Jupiter or even Saturn and a couple  of
> fragments sling-shotted at the Earth.

Multiple asteroids are fairly common, so multiple impacts certainly 
happens. However these would usually occur within seconds of each other, 
and not be noticeable as multiple except near the impact sites. Co-orbital 
comet fragments could certainly impact over a period of several hours in 
different parts of the World. However it is doubtful if the fallback 
deposits far from the impact sites would be separable in this case either. 
In any case the Chicxulub impactor was a chondrite, not a comet as shown by 
the composition of the impact debris.

The only two mechanisms that would result in multiple impacts spread out 
over a longish period (e. g. 300 000 years) are:

1). A comet shower caused by disturbance of the Oort cloud (e. g. by 
another sun passing close to the solar system)

2). A largish collision in the asteroid belt

3). A change in the orbit of one or more of the outer planets causing 
"resonance sweeping" in the Kuiper and/or asteroid belt.

It seems likely that either 1) or 2) may  have caused the striking 
concentration of impacts in the late Eocene.
3)  might seem outlandish but is the most likely explanation for "the late 
heavy bombardment"  ca 3800-3900 MYA BP

> For that matter, what proof is there that the initiation of the Deccan Trap
> lava flows was not caused by a meteorite/comet fragment impact?

It is indeed possible that *very* large impacts might generate lava on a 
large scale. There is no definite proof that this has happened on Earth 
(except on a small scale at Sudbury), but there is one clear case on Venus, 
so it can happen.
It has been suggested that The Siberian Traps, the Ontong Java Plateau or 
the Bushveld complex of South Africa might have originated in this way, but 
the arguments aren't very strong.
In any case, as others have already pointed out, Deccan volcanism started 
well before the end of the Cretaceous. Also note that there are dinosaurs 
and other typical maastrichtian fossils in the intertrappan beds, so at 
least the early part of the Deccan eruptions did not have too catastrophic 
effects even on the (then insular) Indian continent. However it is clear 
that even fissure eruptions of modest size have severe effects over 
considerable areas as shown by the Laki eruption 1783 which caused mass 
mortality in sheep and cattle and a consequent famine on Iceland.

Tommy Tyrberg