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Dating of fossils by scientists

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Early geologists, in the 1700s and 1800s, noticed how fossils seemed to occur in sequences: certain assemblages of fossils were always found below other assemblages. Since 1859, paleontologists, or fossil experts, have searched the world for fossils.

In the past 150 years they have not found any fossils that Darwin would not have expected.

As the isotopes decay, they give off particles from their nucleus and become a different isotope.

The parent isotope is the original unstable isotope, and daughter isotopes are the stable product of the decay. In the first 5,730 years, the organism will lose half of its C-14 isotopes.

For example, techniques based on isotopes with half lives in the thousands of years, such as Carbon-14, cannot be used to date materials that have ages on the order of billions of years, as the detectable amounts of the radioactive atoms and their decayed daughter isotopes will be too small to measure within the uncertainty of the instruments.

One of the most widely used and well-known absolute dating techniques is carbon-14 (or radiocarbon) dating, which is used to date organic remains.

Other critics, perhaps more familiar with the data, question certain aspects of the quality of the fossil record and of its dating.

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Some scientists prefer the terms chronometric or calendar dating, as use of the word "absolute" implies an unwarranted certainty of accuracy.

Techniques include tree rings in timbers, radiocarbon dating of wood or bones, and trapped charge dating methods such as thermoluminescence dating of glazed ceramics.

Coins found in excavations may have their production date written on them, or there may be written records describing the coin and when it was used, allowing the site to be associated with a particular calendar year.

The mass spectrometer is able to give information about the type and amount of isotopes found in the rock.

Scientists find the ratio of parent isotope to daughter isotope.