The Ages and The Dating Methods
One of the most reliable methods used today in absolute-age dating of the ancients is radioactive dating, using uranium:
The sum of uranium 248 plus lead 206 is always constant over time because uranium 248 decays into lead 206 in time. Knowing that uranium 248 has a half-life of 4.5 billion years, scientists are able to determine the ages of the ancient substances, such as rocks. (e.g. The age of solar system has thus been calculated to be approximately 4.6 billion years old using the oldest meteorite found.)
The most popular dating method for the relative age, on the other hand, is the appliation of the law of superposition, by James Hutton. As a geologist, Hutton noticed that older sediments were deposited prior to more recent ones, thus are physically positioned below the more recent ones. Therefore, combining the law of superpostion and the usage of index fossils, relative ages of fossils could be obtained within tolerable precisions.
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