|MadSci Network: Earth Sciences|
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
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