AGE OF THE EARTH
I have copied this from the ICR website:
VII. Deduction of 10,000-Year Age Limit on the Earth.
Knowing the half-life of the earth's magnetic moment, one may easily work backwards to set up an historical schedule of the earth's magnetic moment and of the associated magnetic field. If that is done, it will be seen that the value of the earth's magnetic field approaches that of a magnetic star if the earth's magnetic field goes back 10,000 years. But a magnetic star has a magnetic field generated by a huge nuclear power source. Surely it is reasonable to assume the constraint that the earth never had such a powerful source and, therefore, never had a magnetic field equal to that of a magnetic star. With that constraint, physics implies a limit on the age of the earth's magnet of less than 10,000 years.
Because there is no known geophysical means, within the last 10,000 years, of starting up the huge magnet in the earth, one is led to conclude that the origin of the magnet was concurrent with the creation of the earth. Hence, the earth also has an age limit of less than 10,000 years.