In the 1970s, the creationist physics professor Dr Thomas Barnes noted that measurements since 1835 have shown that the earth's magnetic field is decaying at 5% per century
Barnes calculated that the current could not have been decaying for more than 10,000 years, or else its original strength would have been large enough to melt the earth. So the earth must be younger than that.
See: http://www.answersingenesis.org/creation/v20/i2/magnetic.asp for a complete explanation.
a. Extrapolated by more than a factor of two or th target="_blank">ree - not scientific.
b. Barne uses selective data; data points are scattered, no line can/should be fit to it.
c. Rate of change (true) may not be steady; if it were, Barnes data says earth is 300 years old.
d. Much evidence that magnetish has oscellated UP and down! Barnes wasn't around when it went up.
e. Hypothesis depends on HIS hypothesis of how the magnetism is formed in the first place which is purely conjecture - hasn't been subjected to rigor.
f. Use of selective data.