The previous post briefly discussed the notions of ‘clock time’ and ‘event time’ in the context of geological thinking. (Note that I’m using and instead of versus — I don’t think we need to pit these against each other in a way that implies a dichotomy.) For this post I’d like to explore the idea what an ‘event’ is in the context of the multiscale temporal reasoning common in geoscience and Earth history. As always, these blog posts aren’t meant to be a comprehensive and exhaustive treatment — the spirit of this is simply to share some thoughts as I read and learn.

What defines an ‘event’? A straight-up google definition is: “a thing that happens, especially one of importance”. Perhaps we could add to this with specifying that an event has a beginning and an end — that is, it is a discrete ‘thing that happens’ in the context of time such that you experience the before, during, and after. For example, we typically don’t refer to a permanent change as an event. But, as I’ll get into below, what’s temporary and what’s permanent can depend on the temporal perspective.

I was recently reading this fantastic 2020 review about paleoclimate research in Science by Jess Tierney and coauthors and decided to use a famous and well-studied Earth history event — the Paleocene-Eocene Thermal Maximum (PETM) — as the inspiration for the example below. That is, what I show below is not strictly based on PETM specifics, think of it more as a generic example to illustrate a broader point.

Okay, let’s set this up. I’ll show a bunch of plots like the one below where time is on the horizontal axis and showing elapsed time progressing from left-to-right. The vertical axis is some ‘change’ in the most generic sense, it could be anything. (For example, in the context of paleoclimate, it might be the values of a measurable proxy that is used to represent temperature, atmospheric CO2, etc.) This first view shows a ‘spike’ occurring at ~1 million years. I think we would all agree this is an event with a beginning and an end, and a clear signal of temporary change in context of background conditions.

Now, let’s ‘zoom in’, in a temporal sense, by changing the horizontal axis to show this event over 150,000 years in the plot below. (If I had the coding skills I would’ve built an interactive widget for you to zoom in/out however you like but, alas, I am not so skilled!) At this scale we can see the ‘shape’ of this event. There is an abrupt beginning and a gradual transition from the peak change back to the pre-event condition.

In the lingo of paleoclimate, we might say that this event has a rapid onset and gradual recovery. In this case, the duration of the onset is only ~5% of the duration of the entire event. This is just one shape, of course. You could envision it in reverse, symmetrical, and so on.

Let’s temporally zoom in more, to the beginning of this event. The plot below shows approximately 10,000 years of time and focuses on that initial change, or onset. Here, we can see that the initial change — going from the baseline to the peak — occurs over 6,000 years. Is 6,000 years ‘rapid’? Additionally, if this was the only temporal perspective we had, would we call this an ‘event’? From this view, this looks like a permanent change.

One of the key timefulness skills is the ability to mentally zoom in and out like this with relative ease. Like any skill that eventually feels natural, it takes practice. Perhaps an additional way to practice is to transpose these geological timescales (millennia to millions of years) to timescales relevant to human experience.

The plot below is the exact same event as above, but with the horizontal (time) axis now in years. Thus, instead of the total duration as 130,000 years, we are considering this change over ~13 years. For adult humans this is a duration that has a ‘feel’ to it. Just as in the PETM-inspired event above, this change as a rapid onset and a gradual transition back to baseline.

We could then zoom in more just as we did above and see that the initial change for this ‘event’ occurred over ~7 months. Again, is seven months ‘rapid’? The obvious quick answer to these questions is, of course, ‘it depends’.

This notion of dependence on timescale-of-investigation is not a new idea in geoscience, of course. These ideas are deeply ingrained in our science and show up in many forms and in numerous contexts. To circle back to the Tierney et al. (2020) Science paper, they make the following statement near the end of the paper regarding temporary changes in climate:

Earth has the ability to recover from a rapid increase in atmospheric CO2 concentration — the PETM is a textbook example of this process. Indeed, in every case of past CO2 perturbation, the Earth system has compensated to avoid a runaway greenhouse or permanent icehouse. Yet the natural recovery from aberrations takes place on geological, not anthropogenic, time scales.

Emphasis mine. They are making this critical point about timescales of Earth-system recovery because the audience, the reader, of their paper may not be as familiar with (or skilled at) adjusting their temporal perspective.

Those that are accustomed to thinking in this multi-timescale way — that is, those that have developed timefulness skills — might consider my examples above as obvious or even trivial. And that, I think, is the point. Could the type of thought exercises above that transpose longer timescales to the range of timescales that humans experience help people develop timefulness? I suspect that many geoscience instructors are already doing things like this in innovative and clever ways, but perhaps in an embedded or implied sense. I’d like to suggest that we be more intentional and highlight temporal reasoning when it is an important aspect of a particular lab activity, problem set, or project. And, in some cases, develop new activities/projects in which temporal reasoning is elevated, where it is the primary learning outcome.

I plan on using future posts to ponder this further and to, hopefully, develop some tangible ideas to use in my teaching. One quick idea to end this post: I could break students into small groups, give each group a different temporal view of some change (the different plots above), ask them to characterize it with both language and quantitatively, and then we convene as an entire class to discuss the differences.