# Age of solar system from radiometric dating

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).

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.Or you can tell that certain parts of the Moon's surface are older than other parts by counting the number of craters per unit area.The old surface will have many craters per area because it has been exposed to space for a long time. If you assume that the impact rate has been constant for the past several billion years, then the number of craters will be proportional to how long the surface is exposed.Carbon-14 dating works well for samples less than about 50,000 to 60,000 years old and for things that were getting their carbon from the air.The long ages (billions of years) given by radioactive dating of rocks seems an impossibly long time for some people.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).

There are always a few astronomy students who ask me the good question (and many others who are too shy to ask), ``what if you don't know the original amount of parent material?

'' or ``what if the rock had some daughter material at the very beginning?

'' The age can still be determined but you have to be more clever in determining it.

One common sense rule to remember is that the number of parent isotope atoms the number of daughter isotope atoms = an unchanging number throughout time.

All atoms of an element have the same number of protons in their nucleus and behave the same way in reactions.