Fossil Correlation for Dummies

Coccolith photomicrograph

Ever ask a general question and get an answer that's strangely specific? We've run across that one before, in an eHow.com answer about pine tree identification. Today's dumbass, overly-specific answer to a simple question comes courtesy of eHow.com (surprised? we're not) and Yasmin Zinni. Oddly, Zinni claims to have been a teacher – a biology teacher, yet – before becoming a "journalist," and before telling us all about "Fossils That Are Most Useful for Correlation" (now niched at Sciencing.com).

Yasmin starts off with a definition more or less cribbed from every beginning geology text:

"To study correlation, geologists prefer common fossils with a wide geographic range, distinctive features and habitats and a short geological duration, which translates to a few million years at most, according to the University of Waikato."

"Yay!" our staff geologist said before reading the remainder of the post, at which time he said, "Crap!" After a fairly good start, Zinni the continues by misinforming her readers that there are three – count 'em, three (or maybe it's four) – "fossils that are most useful for correlation": coccoliths; trilobites; and "Pectea and Neptunea," Cenozoic mollusks. The sign on your local Shell gas station is a stylized pecten shell, so that's a pretty good correlation for gasoline sales...

The real answer? it isn't the class Trilobita, little calcium plates from calcareous algae or a class or two of mollusks. The real answer is

Index Fossils: common fossil genera that have a wide geographic distribution, but whose appearance on the geological time scale is relatively brief. Index fossils are also sometimes called key fossils or zone fossils. 

That's all that was necessary... but Yasmin had already said that, so she felt compelled to list some index fossils. Her list, however, appeared in a vacuum and was thus less than useless; it was confusing. More to the point, it was ridiculously incomplete. Zinni also made a classic error in describing coccoliths when she said,  "Coccoliths are marine microorganisms able to convert carbon dioxide dissolved in the water in calcium carbonate."

That's not what a coccolith is; that's what a coccolithophore is. Coccolithophores are single-celled calcareous algae; the coccoliths are tiny plates of calcium carbonate (calcite) that the algae assemble into a test or shell. If you're going to crib, Yasmin, at least copy it right! Oh, yeah, and by the by: geologists don't "study" correlation, they perform correlation. Dumbass.

An overly specific answer to a general question augmented by misinformation: that's the recipe that led the Antisocial Network to award Yasmin Zinni our coveted Dumbass of the Day.

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