From: cain@geomag.gly.fsu.edu (Joe Cain)
Subject: Re: Magnetic Shifts, Climate, and Evolution
Followup-To: sci.geo.geology
Organization: Florida State University Geology Dept.
Date: Thu, 8 Oct 92 19:52:26 GMT

In article <1992Oct7.215130.22194@eos.arc.nasa.gov> kyrsten@eos.arc.nasa.gov (Kyrsten Swazey) writes:

>My archaeology professor stated that the pole reversals were possibly
>attributable to magma sloshing around in the earth's core.  Iron magma,
>i believe, which would "cause" the pole reversals as it slooshed from
>relatively one side to the other... the transitional period causes the
>magnetosphere to fluctuate.  Specifically, to weaken, correct?

The reversals of field are more likely due to instabilities in the
hydromagnetic process of generation, or small flow changes, not major changes in
the core flow. Accretion of insulating material temporarily near the
core-mantle boundary for example, has been suggested by Stacy as a
pertubation due to its allowing temperature to build up in one region.

>  Which would allow more solar radiation to enter the earth's atmosphere, which
>could increase the earth's temperature, thus inducing a cooling trend:
>an ice age.

Lets, see..more solar radiation => cooler?? I don't quite follow the
logic here even if decreasing the size of the magnetosphere might have
such an effect, or any effect.  

>Now astronomy comes into play.  The sun has cycles.  There are 11-year
>ones which i kinda think of as days.  But there are also much longer,
>more pronounced ones ("years"?!?).  So, the sun could be fluctuating in
>a relatively regular manner which, over billions of years, gradually
>slows and becomes less pronounced.  Perhaps the reason why magnetic
>shifts are not *always* connected with ice ages is due to these solar
>fluctuations.

The long term history of the Sun is supposedly one of slowly
increasing energy output, though perhaps not monotonically. 

>The connection between glaciations and evolution is relatively
>well-established, correct?

	I would be interested in hearing of and understanding the
latest information on the ideas regarding the interactions between
life and glaciations, etc if some knowledgeable person would summarize
them.  The factors are complex and must include variations in the
weather patterns with changes in the orbital aspect of the Earth due
to precession, small changes in obliquity and eccentricity. Also, the
interaction with a decreasing amount of carbon dioxide as life began
to add oxygen, perhaps some significant change in albedo as more water
was condensed, the change from acidic to near neutral oceans
and the precipitation of ferrous solutions, the Earth's internal
temperatures cooling, the continents becoming larger (and moving to
different latitudes in different configurations). I heard from a
colleague today that perhaps some of the evolutionary spurts may have
benefitted from a glaciation. Then there is the complication of
episodic events such as massive volcanic eruptions, major meteoroid
impacts, etc.  

	
>What about the fact that glaciations are apparently coming in closer
>succession?
	
Hmm, can someone summarize the glaciations or point to a reference
containing such a summary?
Joseph Cain		cain@geomag.gly.fsu.edu
cain@fsu.bitnet		scri::cain
Newsgroups: sci.geo.geology