Tuesday, September 29, 2020

Vastly Different Timescales

This is a wandering exposition on the challenge of understanding geological and paleontological timescales and whether we . . . well, whether I am up to the task.

The Aquia Formation is exposed at Purse State Park, located just south of Liverpool Point on the Maryland side of the Potomac River.  It rewards fossil hunters with an abundance of riches dating back to the Late Paleocene epoch, that is, some 59 to 56 million years ago.  Among the most prevalent fossil shark teeth found here are those from Striatolamia striata, a sand tiger shark.  Though distinguishing sand tigers as to species poses a challenge, I believe the teeth shown below are from S. striata (for more on these teeth, see Bretton W. Kent’s Fossil Sharks of the Chesapeake Bay Region (1994)):


Millions upon millions of years ago.  Numbers like 56 million years ago, much less some 350 million years ago deep in the Mississippian Period (I'll return to that at the end of the post), or, better yet, 4.5 billion years ago with the formation of Earth, or 13.8 billion years ago marking the origin of the universe – these all, I think, challenge our understanding.  Geology and paleontology, as well as astronomy, bring us face to face with periods of time on timescales that render insignificant (to the point of nothingness) the timescale with which we are most intimately familiar:  our lifespans.  That is the timescale that makes most sense to us and, as a result, that familiarity may confound comprehension of the periods of time and timescales that paleontologist, geologists, and astronomers work with.

What might it mean to “understand” timescales in millions or billions of years?  I’m really not sure.  Science educators regularly face the challenge of teaching students about these timescales and these huge blocks of time.  It appears that among the key measures of understanding in that context is whether students can work with these vast expanses of time to describe properly a succession of geologic and evolutionary events that occur across these periods, and to describe the duration of some geologic and evolutionary processes.  The former seems easier for most to grasp than the latter, given some prevalent misperceptions about the relationships among rate, size, and duration.  (See, Kim A. Cheek, Exploring the Relationship Between Students’ Understanding of Conventional Time and Deep (Geologic) Time, International Journal of Science Education, 2011.)]

This is, I think, too narrow a definition of understanding in this context.  I assume individuals could demonstrate a comprehension of succession and duration using these timescales without grasping the scientific or the personal implications of them.

Actually, the initial task in trying to truly understand what timescales of this magnitude mean may be making sense of large numbers in the first place.  In a recent article about whether and how we can grasp the extent of fatalities from COVID-19, science writer Sarah Elizabeth Richards wrote:

Ultimately, our biology is working against us.  Researchers say our brains aren’t wired to make sense of big numbers.  (Why Our Minds Can’t Make Sense of COVID-19’s Enormous Death Toll, National Geographic, September, 2020.)  

Is that right?  I do think there may be a hard truth here which affects how we are able, or, rather, unable to understand the timescales in geology, paleontology, and astronomy.  Mathematician Tobias Dantzig observed that historically many societies began with only a limited concept of number, counting a few objects and then immediately segueing to the whole, e.g., “one, two, many.”  (Number:  The Language of Science, 3rd edition, 1945.)  This phenomenon is embedded in most European languages.  For instance, the old-fashioned adverb thrice in English means not only “three times” but also “extremely, very.”  (Compact Oxford English Dictionary, 2003.)  “She was thrice blessed” could mean she was blessed three times or she was extremely blessed.

So, we begin by distinguishing a few – the ones we count – from the many, almost regardless of the magnitude of that “many.”  Perhaps we are still inclined to do that.

Physicist Ross McCluney asserted that we attempt to grasp large numbers using a particular strategy:

We humans are well-developed to see subtle differences in things, while absolute magnitudes can escape us.  Thus we best perceive the sizes of things by relating them to something else, to some standard of size with which we can compare them.  (Conveying Large Numbers to General Audiences, Bridges:  Mathematical Connections in Art, Music, and Science, 1998, p. 170.)

That may be an important step – find the reference set of comparative measurements that make some sense of these large numbers.

The preeminent science writer John McPhee puzzled over this very issue as he explored geology in his wonderful Basin and Range (1981).  Geology, McPhee remarked, brings us face to face with deep time (he coined this term), numbers of years in the millions and billions.

Geologists, dealing always with deep time, find that it seeps into their beings and affects them in various ways. . . .  In geologists’ own lives, the least effect of time is that they think in two languages, function on two different scales.  (p. 128)

Geologists are, as McCluney suggested, inclined to come up with some more easily comprehended scales to help them, as well as the rest of us, relate to the magnitude of the geologic timescales.  McPhee described one such comparative scale that I particularly enjoyed.

With your arms spread wide . . . to represent all time on earth, look at one hand with its line of life.  The Cambrian begins in the wrist, and the Permian Extinction is at the outer end of the palm.  All of the Cenozoic is in a fingerprint, and in a single stroke with a medium-grained nail file you could eradicate human history.  (p. 126)

Does that help?  There is both amazement and terror attendant on how strikingly insignificant the lifespan of complex life on Earth has been relative to the age of the planet.  Perhaps more discomforting for our egos is the realization of how nearly invisible in this timescale is the presence of humans.  (Remarkable and horrifying to think what humans have done in that blink.)  Going still deeper into the source of our growing unease, we find it renders invisible the time each of us has individually.

To bring this back to the deep time example that started this post, does a more familiar scale involving outstretched hands representing the span of Earth's existence make the age of the S. striata teeth I found at Purse more easily comprehensible?  A single line of one whorl in the fingerprint may, I guess, represent the duration of the Late Paleocene when S. striata flourished.  In the scheme of things that is a vanishingly small period of time.

Curious, although it covers several million years of time, the Late Paleocene is both a very long time period and nearly no time at all.  It all depends upon our frame of reference. 

If all time on Earth is too long a frame of reference, we might try a different scale, using the extended arms to represent the period from the Cambrian to the present.  In that case, the Paleozoic runs from the tip of my extended right hand to a bit short of my opposite shoulder; the Mesozoic extends from that point to the base of my left hand; and the Cenozoic barely reaches across the palm to the tip of my index finger.  The Late Paleocene featuring my fossil sand tiger teeth is a narrow strip of skin a third of an inch high a bit into my palm.  Does that help?  Probably not, I’m still left with conflicting perceptions of this length of time.

In the end, I may find truly understanding 56 million years as challenging as comprehending the scope and consequences of  billions of years.  Yes, I recognize that both are very long periods of time, and that 56 million is very much less than billions upon billions.  Yes, I can demonstrate a mastery of succession and duration when addressing aspects of these timescales for geological and paleontological phenomena.  But perhaps not much more.

My difficulty may be inherent in the human beast as science writer Sarah Elizabeth Richards stated.  Much earlier than Richards, McPhee observed the same, positing that I and my fellow human beings may be mostly incapable of reckoning with ages on such orders of magnitude.

The human consciousness may have begun to leap and boil some sunny day in the Pleistocene, but the race by and large has retained the essence of its animal sense of time.  People think in five generations – two ahead, two behind – with heavy concentration on the one in the middle.  Possibly that is tragic, and possibly there is no choice.  The human mind may not have evolved enough to be able to comprehend deep time.  It may only be able to measure it.  (p. 127)

(I’m not sure what the tragedy is in that.)

The key to the phenomenon McPhee identified is, I think, that five generations are periods of time which we may have directly experienced ourselves.  We ourselves may move through each of those generations:  we have been grandchildren and children, we have had parents and grandparents.  These are blocks of time we are likely to know intimately (we put a face to a parent or a grandparent), giving us a scale that we can intellectually and emotionally comprehend.  When we compare that scale to far greater numbers of years, a certain degree of terror may set in – each of us is, in fact, less than a blip in the overall scheme of things in the cosmos or on this planet.

As we expand our view beyond that spread of five generation period (covering, say, roughly 100 to 150 years), perhaps we’re back to “one, two, many” if only to maintain some sense of self and step back from the full implications of deep time.

It is true that, at times, when different timescales abut, the phenomenon need not be disquieting.  That’s made clear by a walk in the park.  Consider the insects, the plants and trees, the birds, the dogs, all living lives at timescales that markedly vary.  At times, we may have a fleeting appreciation of what that means about the complexity and fragility of life.  Significantly, during this walk in the park, most of the timescales we might encounter aren’t incomprehensible to us, primarily because they cover periods of time we ourselves have experienced – a few days, a few months, a small clutch of years.

A recent blog post by Kentuckiana Mike for Louisville Fossils is what started me thinking about the difficulty understanding paleontological or geological timescales.  When our quotidian blocks of lived time are put beside timescales that bear no resemblance to those with which we are familiar, the issue is joined.  He illuminated this by implicitly contrasting a timescale measured in millions of years with one measured in a human lifespan.  In this post, he wrote about visiting his family’s cemetery marker where his grandparents are buried.  He presented pictures of the fossils embedded in the rock of which that marker was made.  He wrote, “The marker is made of Bedford(?) limestone.  Time and the elements has eroded part of the surface revealing small crinoid stems and a cross section of a horn coral.  Fossils date from Mississippian Period.”  So, here we go back two human generations and, also, back 359 to 323 million years.  I comprehend the former, perhaps not the latter.


No comments:

Post a Comment

 
Nature Blog Network