THE DEVIL IS IN THE DETAILS – CLEARLY COMMUNICATING CONCEPTS OF THE GEOLOGIC TIME SCALE

An important aspect of the geologic time scale is clear and concise communication to both the scientific community and society at large. This forum is a good place to point out two features of the geologic time scale where we, as scientists, could improve.

“What is our zero?” According to the International Organization for Standards, a time scale is “a system of ordered marks which can be attributed to instants on the time axis, one instant being chosen as the origin.” I was trained that zero was calendar year 1950, specifically January 1 when this detail mattered. A literature search reveals that zero may be 1950, 2000, the collection date, or the measurement date (sometimes mixed in the same journal article). This forum is not the place to advocate for one choice or another, but it is the place to alert stakeholders to the need to come to an agreement on the zero point.

“How do we display our scale?” Within the geoscience community, it seems to be standard that, if the time axis is vertical, older is down and younger is up. Unfortunately, if the time axis is horizontal, readers are on their own. Sometimes older is to the left; sometimes to the right. This forum is an appropriate venue to advocate for a consistent format of OLDER TO THE LEFT. Many modern graphing programs default to higher values on the right. Just as historians would not plot 500 BCE to the right of 300 BCE, we should not plot 500 Ma to the right of 300 Ma. Anyone who is attempting to use a geologic time scale in publication can and should find the appropriate menu item to choose “values in reverse order.” We owe it to our readers to avoid confusion, not to contribute to it.