Thomas G. Barnes, Emeritus Professor of Physics at the University of Texas, El Paso, and a creationist, argues that the geomagnetic field was created by unknown processes at the time of creation of the earth and has been decaying irreversibly and exponentially, with a half-life of about 1400 years, since then. He calculates that the field would have been impossibly large in 8000 B.C. and concludes that the earth, therefore, is less than 10,000 years old. He denies that the earth's field has reversed polarity in the past, and attempts to refute the dynamo theory of the origin of the field. Barnes' arguments and conclusions are commonly cited in creationist literature as definitive proof that the earth is very young. Barnes is wrong, and has ignored or misrepresented much of the data on the earth's magnetic field.

Barnes calculations are based on observatory measurements showing that the earth's dipole field strength has decreased since 1835. But these same measurements also show a corresponding increase in the strength of the nondipole field so that the total field energy external to the core has remained about constant. Paleomagnetic evidence shows that the earth's field has existed for more than three billion years, and that the dipole field both fluctuates in strength and irregularly reverses polarity. The earth's field is generated by a fluid dynamo in the iron-nickel core; all of the elements necessary for a dynamo, including fluid motion and energy sources, are present. Contrary to Barnes' assertions, there are no theoretical reasons why a dynamo cannot exist in the earth.

There are no properties of the magnetid field that can be used to place an upper limit on the earth's age.