Stop the Clocks (and the Other Geologic Timescale Metaphors, Too)!

Leonard Finkelman writes...

Everyone has their own "before" and "after" moment: the event that marks some important distinction in history. For some, the event can be a deeply personal one such as the birth of a child or the death of a beloved friend. For others, it's the Titanic.

A colleague recently gave a paleontology lecture to some local grade schoolers. Her lecture focused on a small collection of fossils from the area. After she presented each fossil, one student's parent would ask, "Was that one before the Titanic?" Every time. Without fail.

It only feels like a geologic epoch before you get to the part when that guy falls off the ship and hits a propeller on his way down. Image courtesy

It only feels like a geologic epoch before you get to the part when that guy falls off the ship and hits a propeller on his way down. Image courtesy

We still don't know if the gentleman in question meant the movie or the ship. I guess it doesn't matter. Twenty years ago might as well be 105 years ago in geological terms. The difference between those two events is short enough that it wouldn't be recorded in the relatively long formation of geological structures; if both events were to show up in the geologic record at all, geologists in the distant future would think that they happened at the same time.

One of the most important parts of education in the earth sciences is communicating the immensity of geologic time. The numbers involved are so mind-bogglingly huge that our best hope for understanding them is by way of various analogies and metaphors. This is a point that's been on my mind as I prepare my first public paleontology lecture (SHAMELESS PLUG). Which of those metaphors is best?

Time and spatial analogies

Here's a (partial) list of some of my favorite facts.

  • My parents started dating in May 1977, which happens to be the same month that Star Wars debuted.
  • The nonavian dinosaurs went extinct 66 million years ago.
  • The first tyrannosauroids appear in the fossil record 160 years ago.
  • Oxygenation of the Earth's atmosphere started three billion years ago and a little less than one billion years ago.

There was a point at which I lumped all of these facts in my "ancient history" mental category. Doing so was a real disservice to my parents, yes. But let's be fair! It was also a disservice to the tyrannosauroids. Our present time is an order of magnitude closer to the emergence of Guanlong than it is to the emergence of a breathable atmosphere. (Also: forty-one years is much, much shorter than the timescale for either of those events.)

It's relatively easy to recognize that fact on an intellectual level. Just do the math! But it's much more difficult to understand the full implications of the math. We use a variety of metaphors to facilitate that understanding.

One of the more popular metaphors employed by science communicators is the Cosmic Calendar.

Like my grading schedule, the Cosmic Calendar is very December-heavy. Image courtesy Wikimedia Commons.

Like my grading schedule, the Cosmic Calendar is very December-heavy. Image courtesy Wikimedia Commons.

The Cosmic Calendar is an analogy between a calendar year and the 14 billion years since the Big Bang. In these terms, the oxygenation of Earth's atmosphere took around three and a half months between September and mid-December, tyrannosauroids (not tyrannosaurids, as depicted in the image above) appeared on Boxing DayT. rex disappeared on the day before New Year's Eve, and my parents started dating after everyone shouted "One!" in the countdown to midnight the next day.

Calendars too linear for you? Try the Cosmic Clock!

Perhaps this is the way may students perceive my hour-long lectures.

Perhaps this is the way may students perceive my hour-long lectures.

This Cosmic Clock ignores all those boring non-Earth years and focuses on the most recent 4.6 billion years of history, collapsing all that time into a single hour. Notice how all of vertebrate history is crammed into the last eight minutes; by comparison, oxygenation takes about half an hour.

Prefer walking to looking at stuff? Various museums have you covered with walkways that measure geologic time in footsteps.

Each of these metaphors works (to some degree or another) by establishing some analogy between space and time. "Look at how much space these geological events take up in this image," each seems to say, "and look at how little space your familiar experiences take up! Now imagine those spaces translating to periods in time!" You're supposed to be awestruck by the analogy's conclusion (sufficiently awestruck, at least, that you don't question where that voice might be coming from).

The effectiveness of these metaphors therefore depends on two things: first, that our perceptions of spatial differences are better than our perceptions of temporal ones; second, that there isn't a strong disanalogy between perceptions of space and perceptions of time. That first point seems safe enough (and here's a way to test it yourself).

(One might argue that we're not much better with large spatial distances than we are with large temporal differences. After all, we've now had two American presidents suggest that NASA establish a moon base to facilitate a trip to Mars, which is like saying that a New Yorker could facilitate a drive to Los Angeles by staying with a friend down the block first. But such cases are less a problem with perception than they are with factual knowledge: the people involved just don't know the quantities involved.)

As for the second point...

Hooked on a feeling

Albert Einstein famously described relativity by offering another analogy: "Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute." There's an important point there that we need to bear in mind when formulating metaphors for geologic timescales.

Einstein's point was really about the nature of space and time. I really, really don't want to get into that. While I respect philosophies of temporal metaphysics, my efforts to engage in discussions about them are best summarized by the first line of this song. (However, I will encourage readers to look into the relevant work of John McTaggart Ellis McTaggart, because someone with a name like that deserves internet fame.)

What Einstein's quote highlights, however, is the phenomenological aspect of time. Immanuel Kant is perhaps the philosopher most famous for arguing that the raw first-person feeling of time's passage is inseparable from our understanding of time per se. The point here is that emotive elements (among others) influence our perceptions of time's passage.

Consider how the passage of time feels at different stages of your life. I remember how summers used to feel as though they last longer than they feel now; if anything, each season now feels shorter than each one that preceded it. Augustine (among other, later philosophers) noted the same phenomenon and argued, in effect, that the feeling of time's passage is diminished by the amount of experience we have with time passing. (This argument has historical significance, in that it's the first non-trivial claim of Augustine's with which I agree.)

This is an important disanalogy between space and time. Since perceptions of spatial distances scale directly--the distance I see covered by two meter sticks is obviously twice as long as the distance I see covered by one--getting more experience with measuring distances should make us better at imagining distances we haven't yet experienced. Time is different, however: as we get more experience with time's passage, we're actually less capable of imagining timespans we haven't experienced. Perceptions of time don't scale directly, and so the way we perceive the time of two days won't be the same as doubling our perception of the first day's time.

The use of metaphor

It should follow, then, that all of the metaphors we use to aid the understanding of geologic timescales are fundamentally flawed. It won't work for me to say, "Has a lot happened in the past year? Now imagine two billion of those years and you'll understand the amount of time it took to fill the Earth's atmosphere with oxygen!" Given how time is perceived, that conclusion is literally impossible to draw. The passage of two billion years would be perceived in a way that's logically distinct from two billion perceptions of a single year.

(You could say that the purpose of the Cosmic Calendar or the Cosmic Clock isn't to offer a spatial analogy, but that doesn't help things. The alternative there is to compare experiences--"extrapolate your experience of three months of time to understand two billion years"--but that wouldn't work either, for the same reasons given above.)

What's the solution, then? I see three possibilities: ignore the problem, accept the problem, or fix the problem.

We ignore the problem if we keep using the same metaphors. They won't really help people to understand geologic time, but what the heck, people are wrong about all kinds of things all the time and they get by just fine. In any event, it doesn't seem as though this lack of understanding prevents good science from getting done, so this is a viable option.

We accept the problem if we recognize the faults of our metaphors and so stop using them. Maybe we just can't understand geologic time at all--too bad for us! I'd imagine this option seems fairly unsatisfying, but I've often said that one of the benefits of philosophy is getting comfortable with the idea that there are things you can't know.

We fix the problem if we recognize the faults of our metaphors and so make a change. Maybe we change the metaphors themselves. We can change the target of our analogies: maybe we're not trying to learn about large amounts of time, but instead about large amounts per se. If this is the case, then there's no need to limit our metaphors for geologic time to things like calendars or clocks; we could also use more generalized metaphors for understand very large numbers. We can also stop trying to give a sense of quantities of time and focus instead on our own limitations. This is what I tend to do: I consider how difficult it would be to imagine a houseplant filling a room with enough oxygen to keep me alive and then stump myself trying to imagine that houseplant filling the planet with enough oxygen to keep everyone alive, and I recognize the value in knowing just how badly I've been stumped. It helps to know that we're unequipped to understand geologic time because that forces us to devise increasingly clever tools to studying it.

My overall point is this: if we really want to play it safe, then we should say that geologic time is like a person whose only point of reference is the Titanic. The workings of such phenomena are mysterious and unfathomable, but still fun to talk about.