Re: Vredefort

["Larry Febo" <larryf@capital.net>]

-----Original Message-----
From: Stanley Friesen <sarima@ix.netcom.com>
To: larryf@capital.net <larryf@capital.net>
Cc: Ilja Nieuwland <nieuwlnd@let.rug.nl>; dinosaur@usc.edu
<dinosaur@usc.edu>
Date: Friday, November 26, 1999 12:10 AM
Subject: Re: Vredefort



>
>
>Certainly a large enough impact could wreak havoc on the crust, and even
>overturn large parts of the mantle.  No such impact has occurred in the
last
>3.5 billion years, of this we can be fairly certain.
>

I`m not so sure. Much may be hidden because of erosion on the Earths
surface, or obliterated by subduction on the oceans floor. If you check out
the website at:
http://gdcinfo.agg.emr.ca/toc.html?/crater/world_craters.html
you can see that there are widespread craters, they are only lacking in
unpopulated (and therefor unsurveyed) areas, and they seem to be of various
ages,...not just in the range of 4 billion years ago. (makes me wonder about
the assumption that all the moon`s craters are also that old!) Also, one
must take into consideration the probability that a large meteor may have
struck in the ocean, where evidence of it`s impact may have been
subducted.One must keep in mind that  there is roughly a 75% chance that
this would be the case.

So,...how much active searching for the larger craters is actually going on?
As I recall, Chixalube (one of the biggest)  wasn`t all that easy to find!


>However, as geologists have known about the impact that produced the Moon
for
>decades, I am sure they have taken that into consideration in modeling the
>driving forces of plate tectonics.  So, it seems unlikely to me that this
sort
>of thing is the origin of the mantle circulation.
>
>
>--------------
>May the peace of God be with you.         sarima@ix.netcom.com
>
>
>