UCSB Science Line
Sponge Spicules Nerve Cells Galaxy Abalone Shell Nickel Succinate X-ray Lens Lupine
UCSB Science Line
Home
How it Works
Ask a Question
Search Topics
Webcasts
Our Scientists
Science Links
Contact Information
How do people determine how old fossils are?
Answer 1:

That's a good question. There are tiny bits of radioactive chemical elements in rocks and fossils. Scientists can tell how old the rocks and fossils are by seeing how much radioactivity is left. Radioactivity has a half-life - that's the time for half of the radioactivity to decay [disappear]. For radioactive carbon - C-14 - the half life is about 6,000 yrs, so after 6,000 yrs, there's half as much C-14, and after about 12,000 yrs, there's a quarter as much C-14. C-14 is good for finding the age of things that are less than about 70,000 yrs.

Some radioactive elements have much longer half-lives, so they're good for dating things up to millions or even a billion yrs old.

Another way to date fossils is to look at the layer of rock where they're found Older rock layers get buried by younger rock layers, so the rock layer on the bottom is the oldest, and the rock layer on the top is the youngest.

This website will tell you more than you want to know!


Click Here to return to the search form.

University of California, Santa Barbara Materials Research Laboratory National Science Foundation
This program is co-sponsored by the National Science Foundation and UCSB School-University Partnerships
Copyright © 2015 The Regents of the University of California,
All Rights Reserved.
UCSB Terms of Use