The third day you eat half again of what's left (leaving 1/8th), and so on until you finish the pie (or get sick of it).If your mom walked in and saw 1/16th of a pie (and knew that you had been eating half of what was left every day), she could quickly determine that the pie was four days old. Some elements (uranium, for example) are unstable, and decay to a different element (uranium to lead, for example).However, in the past few hundred years many people have been more inclined to use the scientific method to date the Earth.
When ‘parent’ uranium-238 decays, for example, it produces subatomic particles, energy and ‘daughter’ lead-206.
For centuries, people were happy to simply accept the teachings of mythology or religion.
These datings put the age of the Earth anywhere from around 7,000 to trillions of years old.
The first day you eat half the pie, and save the other half for later.
The second day you eat half of what's left (leaving 1/4 of the original pie).