Because the earth’s magnetic field is declining
My 16th reason I believe the Earth is young is: Information gathered from “Magsat” (meaning magnetic field satellite) confirmed what scientists have thought: the earth’s magnetic field is weakening. In fact estimates are that in just 1,200 years it will reach zero (Editors, “Magsat Down, Magnetic Field Declining,” Science News, vol. 117, June 28, 1980). What are the concerns? Well, many, but one is that we would lose our primary radiation shield. Thomas Barnes from the University of Texas, El Paso, stated that according to best measurements he would say the earth could not be more than 15,000-20,000 years old (“Satellite Observations Confirm the Decline of the Earth’s Magnetic Field,” July 21, 1980, University of Texas, El Paso, TX).
From Roger’s book The Bible and Science Agree the Earth is Young