To determine absolute age, the two primary methods are:
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Radiometric Dating: This includes techniques like carbon-14 dating, which measures the decay of carbon-14 in organic materials to provide an age estimate up to about 50,000 years. Other isotopes (such as uranium-lead, potassium-argon, etc.) are used for dating older geological formations.
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Dendrochronology: This is the study of tree rings, which can be used to date the precise year in which a tree was formed, thereby providing information on the age of the tree and the surrounding environmental conditions.
In contrast, the Law of Superposition is used to determine the relative age of geological layers, not absolute age. It states that in undisturbed sedimentary rock layers, the oldest layers are at the bottom and the youngest are at the top.