Uses of isotopes in radioactive dating

Before then, the Bible had provided the only estimate for the age of the world: about 6,000 years, with Genesis as the history book.Hutton's theories were short on evidence at first, but by 1830 most scientists concurred that Noah's ark was more allegory than reality as they documented geological layering.

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

Using fossils as guides, they began to piece together a crude history of Earth, but it was an imperfect history.

After all, the ever-changing Earth rarely left a complete geological record.

For example, if a rock is analyzed and is found to contain a certain amount of uranium-235 and a certain amount of its daughter isotope, we can conclude that a certain fraction of the original uranium-235 has radioactively decayed.

If half of the uranium has decayed, then the rock has an age of one half-life of uranium-235, or about 4.5 × 10 y.

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