Topic 10a: SAYONARA T-REX AND THE GEOENVIRONMENT

A current topic of intense debate, the current debate on
extinction of the dinosaurs shows how scientific ideas arise,
are proposed, develop into hypotheses, rise to the status of theory,
are attacked by some and defended by others (so, they are "tested"),
and are accepted by a generation of scientists, or discarded.  So it
will be interesting for you to look back in 20 or 30 years and see 
how this idea works out.  At the moment it looks like the evidence
is good for (several, maybe 3) meteor(?) impacts within a meter or so
of rock, involving both sides of the K/T boundary.  And, the evidence
is strong for the extinction of a number of genera around this time,
including the last of the large dinosaurs.  So, did the impact wipe
them out?  Or were they dying out gradually anyway, due perhaps to
changes in "Geo-environment" related to plate tectonics influences on
continental and marine land/sea relations and climate?  If the
latter, perhaps they were genetically weakened to the point that
the impact could knock them off; but their lives were "numbered"
anyway, so they might not have lived much longer even if the
impact had not occurred.  Some new ideas by a Penn State prof, 
presented at this years (1996) Geological Society of America
meeting in Denver, are related to this issue; see below.

Cretaceous-Tertiary (K/T) Boundary - Most dinosaurs disappeared 65 million years ago

Evidence for an impact  -  Layer of ash deposited worldwide.  The ash contains:
-- Rare earth element iridium more abundant than in earth.
-- Spherules of glass caused by melting during impact.
-- Quartz grains with shocked lamellae.

Effects of a large impact:

Immediate - Blast wave, base surge (dust cloud), tsunamis, vaporization of 
water and rock, earthquakes.

Short Term but Global (days to weeks)  -  global distribution of ejecta, 
global wildfires.

Long Term Global Effects (months to years) - Acid rain, Global darkness, 
Greenhouse effect.

Manicouagan Crater, Quebec - 210 million years ago, half the size of the 
state of Connecticut.

Periodic extinction (every 26 million years) - Nemesis Theory which is that 
a companion star orbits our Sun over a period of 26 million years.  The 
companion star is in a highly elliptical orbit passing through the Oort 
Cloud of comets outside of Pluto's orbit.  On passing through the Oort cloud 
the gravitational field of the companion star throws many of the comets 
toward the earth.

NEED TO ADD:Stuff to add on Cuffey.