🚀 go-pugleaf

Ok, as a physicist and a geologist, I think this whole mess needs to be 
cleared up once and for all.  Short lession in science history, as well 
as geology follows.

For a long time, catastrophism was considered to be the primary shaping 
event of the world (ie, volcanos, and big nasty events causing large 
changes) that happen in a relatively short time.  Then beginning in the 
1700's, but having most work on it done in the 1800's, the theory of 
uniformitarianism came into being, which basically says that slow events 
over a long period of time have a significant effect, which holds quite 
true.  Sedimentation of limestone in oceans, and the process of mountain 
building (which continues in many ranges to this day) are events that 
aren't formed in days, weeks, years, or even thousands of years, but on 
the scale of hundreds of thousands to millions of years.

Uniformitarianism became so popular that for a while catastrophic events 
were considered minor players in world events, basically considered 
having local effects only.  Of course, a more centrist view of the 
situation, allowing for both situations is pretty much accepted today.

On the subject of the impact about 65 million years ago - a short history:

In 1978, a group of scientists (including geologist Walter Alvarez, and 
his father Luis Alvares, a Nobel psysicist) were trying out a new 
technique to get the time it took for marine rock layers to form by 
looking at the trace element Iridium.  Iridium is a VERY rare element on 
Earth, but trace ammounts are collected from space dust that is captured 
by the earth (lots of dust and other materials from space is constantly 
raining down - several hundreds of tons a year or more).   Since the rate 
of dust/iridium accumulation is known well enough to suit error factors 
for geological ages, it was a sound model.  But the Alvarez's discovered 
something completly by accident - an EXTREMELY high concentration of 
Iridium in a small layer right at the boundry between the Cretaceous 
(denoted as a K, from the German word) - which was the last age of the 
dinosaurs, and the Tertiary (Symbolized by a T) - the age when mamals pretty 
much took over.  

There's only two possibilities for this concentration of Iridium - a 
volcanic eruption that includes lava from deep in the mantle of the 
Earth, or from an extraterrestrial (meteor or comet) imact, as iridium is 
known to be in high concentrations in such objects.  Further, other 
scientists started noticing that this anomalously high iridium boundry 
was seen globally at the same location in the geologic time scale (at the 
K-T boundry).   Also, it was well known that there are NO dinosaur 
fossils above the Cretaceous, and that about 60% of all other life on 
earth at the time went extinct as well (so it wasn't just a dino problem).

More recent studies of the KT boundry have shown an isotopic ratio of 
Iridium and other rare earth elements (Osmium for one) to be more 
consistent with an extraterrestrial origin, as well as the varieties of 
shocked quartz (quartz that has been changed due to a large stress such 
as an impact) that has been found globally at this layer.

It should be noted, however, that there was a VERY large volcanic 
eruption in the Decan Traps in Russia at about the same time, and recent 
hypothesis abound right now as to them being coincidences, or possibly the 
impact (which was known to be VERY large) causing the vulcanism.  I'm not 
well versed in these hypothesis, however, and will not discuss them 
further without more information.

Nevertheless, it is nearly globally admitted by geologists that an 
extremely large impact occured about 65 million years ago, most probably 
at Chixilub (sorry if this is a misspelling) off the Yucatan Peninsula of 
Mexico, from an object probably in the range of 5 to 10 miles in 
diameter, and there is much evidence supporting this hypothesis.

As far as continental drift goes, it's been going on for a LOT longer 
than 65 million years ago (in fact, it's been going on as long as there 
have been continents) and supercontinents seem to form in cycles (note, 
this doesn't mean all the pieces go back in the same position they used 
to be in at all - they just come together, then break up again, meeting 
each other in different configurations).  There has been at least 4 of 
these supercontinents estimated to have existed, and possibly more.  One 
only needs to go to East Africa and look at the African rift system to 
see a new ocean beginning to form as the rift splits aparts, or come here 
to Duluth and see one that started about 1.1 billion years ago, but 
stopped again (not uncommon).

As for the asteroid belt, to the best of my knowledge, the total mass 
would only be that of a small planet or moon, but it is unlikely that it 
was every together.  It is basically bits left over from the formation of 
the solar system that was caught in a gravitationally good spot, being 
influenced by jupiter.  And contrary to some beliefs, mostly enfoced by 
hollywood, the asteroids are concentrated in two groups, slightly ahead 
of and behind Jupiter's orbit due to orbital mechanics/gravitational 
effects.  I'm sure someone else could explain it better, but I'll find 
more information if people really request it.

I should present a show on this whole thing at the Alworth Planetarium 
where I work ;o).  Or at least hope a representative from a college that 
has a graduate program in planetary sciences might seem impressed and 
send me material on their program ;o).

Hope this helps!

--
/  ALSO SPRACH RFENTIMA / Robert Fentiman - University of Minnesota, Duluth  \
| Amiga 3000/25/9/100  \ rfentima@ub.d.umn.edu or  Robert.A.Fentiman@umn.edu / 
|__MST3K+Starwars+B5 Fan_\______Physics/Geology_Major_-_CS/Math Minor_______/
\_____________Pain is the body's way of saying "Don't do that!"____________/