Fossil Vocabulary

Within those layers, we find clues of various kinds. One of those varieties of information is fossils. Earth is a planet that has hosted life for most of its 4½ billion years, and especially for the last ½ billion years, there have been plenty of animal skeletons and plant tissues to be included in the strata as clues to when they were deposited. For instance, with the Japanese cherts we just examined; we know how old they are based on the fossil radiolaria that they contain.

Stacks of old newspapers, ready for reading or recycling. The words in these periodicals are clues to when they were published, like fossils in strata are clues to when those strata were deposited.

Consider an analogy: these piles of old newspapers. Imagine reaching into these stacks and extracting three pages at random. You read them, and find many familiar words and phrases: each is written in English. But also on each of them, you see distinctive words and phrases:

• • On one: Hepcat. Daddy-O. Supermurgitroid. Peepers. Knuckle sandwich. Made in the shade.
  • On another: Moxie. Bee’s knees. Gams. Flapper. Sockdollager. Zozzled.
  • On a third: Fain. Forsooth. Betwixt. Thou. Verily. Swain. Hugger-mugger.

These words are all archaic in some sense (i.e., they are no longer in widespread use), but they are also specific to certain periods of time (as well as to English-speaking areas of the world). One set of words derives from the 1950s, another from the roaring 1920s, and the last from Elizabethan England (~1600, as recorded by William Shakespeare). The words alone evoke the time in which the newspaper was written.

Trilobite fossil.

Similarly, in historical geology, fossils are the rich vocabulary that serves to indelibly mark their strata with the time of their formation. Some sediments speak a strain of Rock with a pachycephalosaur patois or a trilobite tone. Others communicate with an ichthyosaur inflection or a brachiopod brogue. As with language, these distinctive fossil “words” are emblematic of a specific time or a specific place, or both. They tell us not only when but also what the environment was like at the time.

While sandstones and shales are enduring elements in the language of Rock, fossils are the slang that changes with time and space. Fossils mark the passage of time and tectonics with their unique lexicon.

You’ll never have a pet Anomalocaris because you live at the wrong time in Earth history.
Photo illustration mashup orchestrated by Callan Bentley.

It would be anachronistic to find an Ordovician fossil in Cretaceous strata like a digital watch on a medieval knight. Shakespeare’s characters never said “groovy” or “coronavirus.” And you can’t buy an Anomalocaris at the pet store today. Certain fossils — the ones most useful for constraining the age and place of formation of their host strata — are distinctive enough that we can rely on them as signals of the origins of the sedimentary strata that host them, markers of particular times or places.