Radioactive dating rocks and fossils

New discoveries have filled in the gaps, and shown us in unimaginable detail the shape of the great ‘tree of life’.Darwin and his contemporaries could never have imagined the improvements in resolution of stratigraphy that have come since 1859, nor guessed what fossils were to be found in the southern continents, nor predicted the huge increase in the number of amateur and professional paleontologists worldwide.The most widely known form of radiometric dating is carbon-14 dating.This is what archaeologists use to determine the age of human-made artifacts. The half-life of carbon-14 is only 5,730 years, so carbon-14 dating is only effective on samples that are less than 50,000 years old.Some of the isotopes used for this purpose are uranium-238, uranium-235 and potassium-40, each of which has a half-life of more than a million years.

Fossils can't form in the igneous rock that usually does contain the isotopes.

Measuring the uranium-to-lead ratios in the oldest rocks on Earth gave scientists an estimated age of the planet of 4.6 billion years.

Segment from A Science Odyssey: "Origins."Geologists have calculated the age of Earth at 4.6 billion years.

Dinosaur bones, on the other hand, are millions of years old -- some fossils are billions of years old.

To determine the ages of these specimens, scientists need an isotope with a very long half-life.

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