Re: age of universe

George Murphy (
Fri, 21 Nov 1997 21:25:37 -0500

McCarrick, Allan wrote:
> Regarding the decay of earth's magnetic field question:
> I've looked at some of the data, and its very true that it is far to
> short at time base to model the remote past (thousands of years). It is
> even more sloppy to pick an exponential model for the data (since a
> linear works much better). I recognize that the exponential model may be
> used because of an a priori "feel" for the right form that the data
> "must" have.

_If_ you assume that the earth's magnetic field was simply set
up initially in a fluid & electrically conducting core, it should decay
exponentially. If you make reasonable estimates for the core
dimensions & conductivity, you get a decay time on the order of a few
thousand years. Whether that really is the mechanism, & whether the
data support this model, are quite different matters.
George Murphy