Re: What is the use of geomagnetic reversals on age dating oceanic crust?

The geomagnetic reversal recorded in the oceanic floor rocks
provides a good and sensitive way to age dating the ocean floor,
because there are a clear and well determined correlation 
between the "magnetic stripes" of oceanic rocks and their ages.

As the geophysical vessels cross the oceans collecting geophysical
data (magnetic among others), some places are drilled for collecting
geological material, in order to analyse the composition and the
age of that rock. This has been done since the early 1960's, so
there are lots of data, and the "calibration" between the age
and the geomagnetic pattern is well determined, to ages from
now to 160 million years, aproximatelly (remember that there
are no oceanic rocks available older than 200 million years,
due to the tectonic processes that "recicles" the oceanic
floor).

So, based in ages obtained by conventional radiometric age
determination, sediments and fossil material, and their
correlation with the well known geomagnetic pattern, the
oceanic floor can be so well dated by this method. This can
be assumed correct (and in fact it is, as far as the geophysicists
know) because the behavior of the magma flow around the mid 
oceanic ridges, that assures a constant and uniform (or,
at least, well studied in many characteristics) flow.

Thanks to professor Igor I. G. Pacca for discussing on this
topic.

Best regards

Eder C. Molina
Dept. of Geophysics
Institute of Astronomy and Geophysics
University of Sao Paulo
BRASIL