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Parent daughter ratio radiometric dating

Over time, radioactive isotopes change into stable isotopes by a process known as radioactive decay.Some radioactive parent isotopes decay almost instantaneously into their stable daughter isotopes; others take billions of years.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.This means that all of the lead 204 on the Earth has been around since the formation of the Earth.Based on extensive sampling of the Earth's crust, scientists determined the present-day abundances of the four isotopes of lead relative to each other and to the parent isotopes that produced three of them.Ideally, the mineral crystals in igneous rocks form a closed system--nothing leaves or enters the crystal once it is formed.

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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.Therefore, their ages indicate when they were formed.Because all parts of the solar system are thought to have formed at the same time (based on the solar nebula theory), the Earth must be the same age as the moon and meteorites--that is, about 4.6 billion years old.The oldest rocks and soils from the moon are about the same age--4.6 billion years old.Scientists assume that meteorites and moon rocks were not subjected to the extensive alteration that Earth rocks have undergone.Note that at time 0, the time of the mineral's formation, the crystal contains only parent atoms.At time 1, 50% of the parent atoms remain; at time 2, only 25% remain, and so on.We know the Earth must be at least as old as any rock on it.Unfortunately, none of the original rocks still exist, so scientists had to use less direct evidence to determine the age of the Earth.If, however, the rock is subjected to intense heat or pressure, some of the parent or daughter isotopes may be driven off.Therefore, scientists perform radiometric dating only on rocks or minerals that have remained closed systems.


  1. Time required for half the number of certain radioactive isotopes to decay to daughter isotopes. Radiometric Dating. If the half life of an isotope is known and the parent/daughter ratio is determined then the age of the sample can be calculated. Calculating the Radiometric Age. For Example -- a parent/daughter ratio of.

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