We will deal with carbon dating first and then with the other dating methods.Carbon has unique properties that are essential for life on Earth. To determine the age of a sample, the SCAR technique uses a highly stable infrared laser to excite carbon dioxide molecules in a mirrored cavity.When the laser is turned off, trapped light dies away in the cavity (or “rings-down”) at a rate that depends on the amount of carbon-For a date, give me a ring.Prior to 1905 the best and most accepted age of the Earth was that proposed by Lord Kelvin based on the amount of time necessary for the Earth to cool to its present temperature from a completely liquid state.
After the passage of two half-lives only 0.25 gram will remain, and after 3 half lives only 0.125 will remain etc.
So, we have a “clock” which starts ticking the moment something dies.
Obviously, this works only for things which were once living.
Familiar to us as the black substance in charred wood, as diamonds, and the graphite in “lead” pencils, carbon comes in several forms, or isotopes.
One rare form has atoms that are 14 times as heavy as hydrogen atoms: carbon-14, or C ratio gets smaller.