# Half life dating rocks

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Isotopes of a given element have the same chemical properties, so a radioactive rock will incorporate the NONradioactively derived proportions of the two isotopes in the Multiply the amount of the non-daughter isotope (isotope B) in the radioactive rock by the ratio of the previous step: (isotope B) × R = initial amount of daughter isotope A that was not the result of decay.

Subtract the initial amount of daughter isotope A from the rock sample to get the amount of daughter isotope A that IS due to radioactive decay.

That number is also the amount of parent that has decayed (remember the rule #parent #daughter = constant). in the age measurements of less than 100 million years.

So the rock is 1 half-life 1 half-life 1 half-life = 3 half-lives old (to get the age in years, simply multiply 3 by the half-life in years).

() is the ``natural logarithm'' (it is the ``ln'' key on a scientific calculator).

Since radioactive rocks have been observed for only a few decades, how do you know you can trust these long half-lives and the long ages derived?

Here are some points to consider: The gamma ray frequencies and intensities produced by radioactive elements in supernova remnants change in the same predictable way as they do here on the Earth.

The number of parent isotopes decreases while the number of daughter isotopes increases but the total of the two added together is a constant.

You need to find how much of the daughter isotopes in the rock (call that isotope ``A'' for below) are the result of a radioactive decay of parent atoms.Radioactive dating gives the Find out how many times you need to multiply (1/2) by itself to get the observed fraction of remaining parent material. If some material has been decaying long enough so that only 1/4 of the radioactive material is left, the sample is 2 half-lives old: 1/4 = (1/2) × (1/2), n =2.After 1 half-life, there is 1/2 of the original amount of the parent left.You then subtract this amount from the total amount of daughter atoms in the rock to get the number of decays that have occurred since the rock solified.Here are the steps: a result of radioactive decay (call that isotope ``B'' for below).When plants absorb carbon-dioxide in the photosynthesis process, some of the carbon dioxide has the carbon-14 atom in the molecule.