Three facts about radiometric dating daddy39s rules for dating my daughter
At any moment, the ratio between them is a measure of the time elapsed, as long as the system remains closed.But if the hourglass were to break (become an open system), sand leaks out and the hourglass is no longer a reliable tool for telling time.One line of evidence involves rocks from outside the Earth--meteorites and moon rocks.Radiometric dating shows that almost all meteorites are between 4.5 and 4.7 billion years old.
Therefore, scientists perform radiometric dating only on rocks or minerals that have remained closed systems.
The rates of decay of various radioactive isotopes have been accurately measured in the laboratory and have been shown to be constant, even in extreme temperatures and pressures.
These rates are usually expressed as the isotope's half-life--that is, the time it takes for one-half of the parent isotopes to decay.
Once scientists have determined the parent-daughter ratio, they can use this measurement along with half-life of the parent to calculate the age of a rock containing the radioactive isotope.
Radiometric dating has shown that very old rocks--3.5 billion years or older--occur on all the continents.
Note that at time 0, the time of the mineral's formation, the crystal contains only parent atoms.