The
area of research in which the paleomagnetic group has been
involved for the longest period of time is the behavior
of the geomagnetic field in the past, in particular, secular
variation, excursions, and polarity reversals. These studies
have entailed sampling volcanic and sedimentary sequences
in the western U.S., Hawaii, Mexico, China and Siberia.
Our ultimate goal in seeking reliable records of ancient
geomagnetic field behavior is to understand the processes
in the core that give rise to the field. For example, the
rapidity with which the magnetic field changes puts constraints
on fluid velocity at the top of the core. Systematic behavior
of the field in particular geographic regions can provide
information about lateral inhomogeneities in the lower mantle
just above the core. Most recently, by comparing paleomagnetic
field behavior with 3-D numerical simulations of the geodynamo
we are learning how the distribution of heat flowing through
the core-mantle boundary may affect the geodynamo.
