Carbon-14 is a radioactive isotope of carbon. Its has a half-life of about 5,730 years. The short half-life of carbon-14 means its cannot be used to date extremely old fossils.Carbon-14 is a radioactive isotope

## Why cant geologists use carbon-14 to date igneous rocks?

But carbon-14 dating wont work on dinosaur bones. 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. Dinosaur bones, on the other hand, are millions of years old -- some fossils are billions of years old.

## Why is carbon-14 not useful for fossils older than 1 million years?

Every 5,730 years, the radioactivity of carbon-14 decays by half. That half-life is critical to radiocarbon dating. Since carbon-12 doesnt decay, its a good benchmark against which to measure carbon-14s inevitable demise. The less radioactivity a carbon-14 isotope emits, the older it is.