About your magnetic field is decreasing is this what you meant?
Barnes's magnetic field argument (1973) or some echo of it. Henry Morris, himself, once praised
it as one of the best arguments for a young earth.
In 1971 Barnes took about 25 measurements of the earth's magnetic field strength (originally assembled by Keith McDonald and Robert Gunst
(1967)) and fitted them to an exponential decay curve. He drew upon Sir Horace Lamb's 1883 paper as theoretical justification for this. Following
the curve backwards in time, Barnes showed that 20,000 years ago the earth's magnetic field would have been impossibly high. Thus, he concluded
that the earth is much younger than 20,000 years.
If so here is a paper on why it is not so... Enjoy...
http://www.infidels.org/library/modern/dave_matson/young-earth/specific_arguments/magnetic_field.html