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Radiometric dating uses what isotopes

However, the age of each fossil primate needs to be determined so that fossils of the same age found in different parts of the world and fossils of different ages can be compared.There are three general approaches that allow scientists to date geological materials and answer the question: "How old is this fossil?Layers that cut across other layers are younger than the layers they cut through (principle of cross-cutting relationships).The principle of superposition builds on the principle of original horizontality.This is the principle of original horizontality: layers of strata are deposited horizontally or nearly horizontally (Figure 2).Thus, any deformations of strata (Figures 2 and 3) must have occurred after the rock was deposited.

Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.

In addition to being tilted horizontally, the layers have been faulted (dashed lines on figure).

Applying the principle of cross-cutting relationships, this fault that offsets the layers of rock must have occurred after the strata were deposited.

Sometimes sedimentary rocks are disturbed by events, such as fault movements, that cut across layers after the rocks were deposited.

This is the principle of cross-cutting relationships.


  1. Isotopes, Half-life years, Effective Dating Range years. Dating Sample, Key Fission Product. Lutetium-176, Hafnium-176, 37.8 billion, early Earth. Uranium-238, Lead-206, 4.468 billion, 10 million to origin of Earth. Uranium-235, Lead-207, 704 million, 10 million to origin of Earth. Rubidium-87, Strontium-87, 48.8 billion.

  2. May 20, 2011. Geologists often need to know the age of material that they find. They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years. This is different to relative dating, which only puts geological events in time order.

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