The magnetic field of the earth
The earth's magnetic field has been a mystery to man ever since 13th-century philosophers first noticed lodestones (magnetic rocks) turning north.1 In 1600, A.D. William Gilbert, Queen Elizabeth's physician, shed light on the mystery by showing that "the terrestrial globe itself is a great magnet."2 Today, scientists think the earth is an electromagnet; the source of the magnetic field is probably a large electric current—billions of amperes—circulating in the earth's fluid core. But there is still a mystery today: How did the current get started, and what keeps it going? Scientists, who assume that the earth is old, conjecture that complicated flows of the fluid in the core somehow started the current and have maintained it for billions of years. However, such "dynamo" theories are complex, implausible, and incomplete. In the last two decades, they have run into serious problems from magnetic observations on earth3 and in the solar system.4 In 1971, Dr. Thomas Barnes, a creationist physicist, proposed that nothing keeps the current in the core going except its own inertia.5 His simple and rigorous "free-decay" theory would mean that the current is running down slowly, like a flywheel without a motor; thus the strength of the earth's magnetic field would be steadily decreasing over the centuries.6 Barnes cited some historical data7 (not well known at the time) showing that the overall strength of the earth's field has indeed steadily declined by about 7% since 1835, when it was first measured. The decay rate depends on the electrical resistance of the earth's core, and the observed rate is consistent with the estimated resistance of materials at core temperatures and pressures. 6,8 The field strength should decrease by a constant percentage each year, and the data are consistent with such a decrease, implying that the field loses half its strength every 1400 years. Such a rapid decay could not have continued for more than about 10,000 years; otherwise the initial strength of the field would have been impossibly high. Since the field probably started when the earth was formed, the present rapid decay of the field is strong evidence for a young earth.
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