All radioactive isotopes have a characteristic half-life (the amount of time that it takes for one half of the original number of atoms of that isotope to decay).By measuring the parent isotope (radioactive) and the daughter isotope (radiogenic) in a system (for example, a rock), we can tell how long the system has been closed (in our example, when the rock formed).It is commonly used in earth science to determine the age of rock formations or features or to figure out how fast geologic processes take place (for example, how fast marine terraces on Santa Cruz island are being uplifted).

uses of uranium lead dating-16

We have also obtained a very similar age by measuring Pb isotopes in materials from earth.

I should mention that the decay constants (basically a value that indicates how fast a certain radioactive isotope will decay) for some of these isotope systems were calculated by assuming that the age of the earth is 4.56 billion years, meaning that we will also calculate an age of 4.56 billion years if we use that decay constant.

There are many radiometric clocks and when applied to appropriate materials, the dating can be very accurate.

As one example, the first minerals to crystallize (condense) from the hot cloud of gasses that surrounded the Sun as it first became a star have been dated to 4568 plus or minus 2 million years....!! Other events on earth can be dated equally well given the right minerals.

The reason that I trust the accuracy of the age that we have determined for the earth (~4.56 billion years) is that we have been able to obtain a very similar result using many different isotopic systems.

Most estimates of the age of the earth come from dating meteorites that have fallen to Earth (because we think that they formed in our solar nebula very close to the time that the earth formed).Obviously, if the substance you are measuring is contaminated, then all you know is the age since contamination, or worse, you don't know anything, because the contamination might be in the opposite direction - suppose, for example, you're looking at radio carbon (carbon 14, which is produced in the atmosphere by cosmic rays, and which decays into nitrogen).Since you are exposed to the atmosphere and contain carbon, if you get oils from your skin onto an archeological artifact, then attempting to date it using radio carbon will fail because you are measuring the age of the oils on your skin, not the age of the artifact.We have dated meteorites using Rb-Sr, Sm-Nd, Pb-Pb, Re-Os, and Lu-Hf isotope systems and have obtained very similar ages.The fact that the age we calculate is reproducible for these different systems is significant.The decay constants for most of these systems have been confirmed in other ways, adding strength to our argument for the age of the earth., so there is one zirconium (Zi) for one silicon (Si) for four oxygen (O).