Information regarding parachute jumping sites may be found in the Airport/Facility directory, which stores thousands of documents on aeronautics information. The Airport/Facility directory is provided by the Federal Aviation Administration, which is a branch under the Department of Transportation.
The 3.9 billion year old rock has undergone three half-lives (3.9 divided by 1.3 = 3). After 3 half-lives, 12.5% of the potassium-40 remains undecayed.
