I confess that I didn’t know the geological conventions for abbreviating time until I started teaching the geology writing class and looked them up. (That’s despite having published a paper on argon-argon geochronology. Sometimes, just doing whatever the co-authors and reviewers say is the right thing to do…) So I don’t have any strong opinions about how to abbreviate lengths of time. But if you do, the Geological Society of America wants to know.
Short version: traditionally, geologists have used different abbreviations for ages (time before present) and duration (amount of time elapsing between two different events). Ages are abbreviated from Latin: Ga (giga-annum) is a billion years, Ma (mega-annum) is a million years, ka (kilo-annum) is a thousand years. Duration, on the other hand, has been abbreviated from “years.” (I’ve seen it abbreviated in a couple of different ways, actually, and I don’t have my USGS style guide to see what the recommendations there are.) There’s a move to use the same abbreviations for both: Ga, Ma, ka, etc., but there’s disagreement. (The main argument for using Ma to represent durations is that geologists are used to thinking about numbers meaning ages: 70 Ma refers to a time in the Cretaceous.)
My take: I don’t have a strong opinion. It takes practice to make the distinction, and my students tend to ask why we need two units, and I don’t really have a problem telling ages from lengths of time. (I can usually handle subtraction, though it’s more difficult when I’m dehydrated at the end of a long day in the field. Pretty much everything is more difficult when I’m dehydrated.) But I’m willing to be convinced.
So what do you think? (If you’ve got a really strong opinion, GSA is taking comments. But I’m happy to listen if you want to lay out your favorite argument here, too.)
(Note to physicists: 10^whatever seconds just is not going to work, or we’ll have to start working in logarithmic time.)