Radiometric Dating for the Dummy Earth Scientist

Indirect dating of fossils

Few freelancers draw as much scorn from the Antisocial Network staffers as the ones who claim to have an educational background for their topic yet totally blow it when they start writing. You know, like the professional basketball player who doesn't know what a three-pointer is, or a carpenter who can't explain how to use a hammer. That's the reason why one of the team flagged "How Is Radioactive Dating Used to Date Fossils?" at Sciencing.com: contributor Carina Fiore claims to have "a B.S.Ed. in Earth-Space Science." This sure doesn't read like it...

The short answer is that radiometric (not radioactive) dating isn't used to date most fossils, for a couple of reasons. First, most organisms don't contain any of the elements typically used in radiometric dating. Second; with few exceptions, none of the original organism remains once it has been fossilized: the organic bits have been replaced by minerals or just rotted away. Now, let's see what Fiore has to say.

For whatever reason, Corina never corrects the usage "radioactive dating." Oops. Then she starts out with the verifiable, although weak, assertion that,

"Many rocks and organisms contain radioactive isotopes, such as U-235 and C-14."

While some (not "many") rocks contain ²³⁵U, few organisms contain any uranium of any atomic weight. And on the same topic; not many rocks contain ¹⁴C because, as Fiore pointed out, the amount that remains after about 50,000 years is negligible. Think how little is left after, say, 1,000,000 years! Next, Corina explains that,

"Fossils are collected along with rocks that occur from the same strata. These samples are carefully cataloged and analyzed with a mass spectrometer."

That would be cool if it were true, but it's not. That's because most of the unstable elements used in radiometric dating are only found in igneous rocks. You know what kind of fossils are found in igneous rocks? Right: none.

The real answer is that fossils are rarely subjected to direct radiometric dating for all the reasons stated above.  Yet it is possible to assign an age to a fossil if the stratum (singular of "strata," Corina) in which it was found is adjacent to an igneous body that can be dated with radioactive minerals. This indirect method has been used to assign numerical age ranges to many fossil species.
You'd think our Dumbass of the Day would have learned that while getting her B.S.Ed... You'd be wrong (Like Corina).

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