Radioactive isotopes used in carbon dating internet dating services for athletes
Radioactive isotopes are used for radioactive dating.
For example, you would use radioactive isotope Carbon-14 to date anything under 70,000 years that was once living.
If half of the uranium has decayed, then the rock has an age of one half-life of uranium-235, or about 4.5 × 10 y.
In another interesting example of radioactive dating, hydrogen-3 dating has been used to verify the stated vintages of some old fine wines.
Carbon 14 is used, mainly by archaeologists, to date bones and other formerly living matter but not normally fossils.
This is because the half-life of that isotope is 5730 years; it is useful for dating up to 50,000 - 60,000 years but no more.
Radioactive isotopes decay from their parent isotope to daughter isotope at a constant rate (under any circumstances).
The rate at which a parent isotope decays to its daughter isotope is considered one half life.
Generally, however, they are useful because either we can detect their radioactivity or we can use the energy they release.
The half-life of radioactive isotopes is unaffected by any environmental factors, so the isotope acts like an internal clock.
For example, if a rock is analyzed and is found to contain a certain amount of uranium-235 and a certain amount of its daughter isotope, we can conclude that a certain fraction of the original uranium-235 has radioactively decayed.
For carbon dating, the isotope used is Carbon-14, which has a half life of 5,700 years. If so, the official definition is "the determination of the age or date of organic matter from the relative proportions of the carbon isotopes carbon-12 and carbon-14 that it contains".
As far back as there were organisms who were able to consume food containing both ordinary carbon and an isotope of carbon; the comparison of the ratios - which pinpoints the time when an organism stopped eating - gives rise to carbon dating.
Carbon dating is one type of radiometric dating, there are others.