How do scientists use the knowledge of radioactive dating

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.Using fossils as guides, they began to piece together a crude history of Earth, but it was an imperfect history.Once all the parents have become daughters, there's no more basis for comparison between the two isotopes.Scientists can't tell whether the clock ran down a few days or millions of years ago.The result is like a radioactive clock that ticks away as unstable isotopes decay into stable ones.You can't predict when a specific unstable atom, or parent, will decay into a stable atom, or daughter.Read on to see what it takes to date a fossil and what volcanic ash has to do with it.Geologist Ralph Harvey and historian Mott Greene explain the principles of radiometric dating and its application in determining the age of Earth.

But for humans whose life span rarely reaches more than 100 years, how can we be so sure of that ancient date? Even the Greeks and Romans realized that layers of sediment in rock signified old age.

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

The age of the planet, though, was important to Charles Darwin and other evolutionary theorists: The biological evidence they were collecting showed that nature needed vastly more time than previously thought to sculpt the world.