In my layman’s cosmology, the anthropic principle says this: our existence implies that the universe must take the shape it does or we wouldn’t be here to perceive it. A universe with even minutely different physical laws wouldn’t include us (which isn’t to say that such universes don’t exist).
An anthropic principle of sorts is also at work in geologic time — the 4.5 billion or so years this planet has existed. For the vast majority of Earth’s history, conditions were unsuitable for the evolution of mammals. (Nor were humans even remotely certain to evolve from those earliest mammals.) We’ve come to exist in the window of time in which we could have come to exist. Or rather, we’ve survived in the window of time in which we can survive. We call a portion of that window “historic time” — not the entire history of our species, but the history that’s part of our cultural record in one form or another, reaching back only several thousand years.
Historic time overlaps with geologic time the way a whale louse overlaps with the blue whale it infests, though the scale of that comparison is too small by several orders of magnitude. And yet it’s all too easy to believe, with the self-importance of a whale louse, that we exist apart from or outside of geologic time. That’s what our experience tells us. The last 10,000 years or so have been relatively uneventful, geologically speaking. Given the overall length of geologic time, it’s likely that any span of 10,000 years or so would be relatively uneventful.
But the Tohoku earthquake and tsunami remind us there’s no guarantee that historic time must be geologically uneventful. They remind us — forcibly, tragically — that, despite vast differences in extent, historic time and geologic time always converge in the present.
An understanding of what’s seismically likely may differ from an understanding of what’s seismically possible.
We’ve been reminded before. But one of the interesting things about humans, psychologically, is how rapidly history loses its tangibility. The eruption of Krakatoa in August 1883 occurred two months before my maternal grandfather was born, putting it within a degree or two of personal connection. And yet, as an event, it’s no more palpable to me or anyone living than the major Sumatra earthquake that preceded Krakatoa by 50 years — or the eruption of the Yellowstone supervolcano 640,000 years ago.
Seismologists were surprised by the magnitude of the Tohoku earthquake, which exceeded their predictions for earthquakes along that fault line. But then seismologists have only had 130 years of earthquakes — at the outside — in which to calibrate their instruments. Realistically, they’ve had much less time than that. Which is to say that an understanding of what’s seismically likely, based on our experience, may come to differ sharply from an understanding of what’s seismically possible.
Perhaps you’ve seen a computer animation showing the breaking apart of Pangaea, the super-continent that existed some 250 million years ago. In animation, the continents “drift” — that is the word, after all — into their present position as though they were running on greased ball bearings. The animation captures the average motion of the continents, a few centimeters a year. An average is an abstraction.
But the tectonic plates that continents rest on neither glide nor drift, nor is their movement abstract. They lurch, heave, resist, yield, bend, fracture, ripping great seams in the planet’s crust, forcing each other down into the mantle below the crust — a process that sounds much more benign when it’s called subduction. None of this happens averagely. It happens momentarily, event by event over eons, generating volcanism and seismic activity on a scale we know almost nothing about, living, as we do, in conditions that allow our existence.
We’re living in geologic time, where catastrophic events capable of dwarfing our outposts of civilization do occur.
The trouble is that we look back at the breaking up of Pangaea and the movement of the continents and think, well, that’s how we got here, as if we’d arrived somewhere special and the process had somehow paused for us. Two hundred and fifty million years from now, another animation might lead its viewers (whoever they may be) to look back at where the continents are now and think the same thing, as though in 2011 we were — as we are — merely a moment in the ongoing migration of the tectonic plates.
Geologically speaking, we manage to be nowhere special (that’s also our location in the universe) and, at the same time, in a period special enough to allow our existence (ditto). Historically speaking we’re someplace unique — here and now — a uniqueness we share with every other moment that has been or will be the present. Some of those moments were placid. Some were and will be violent beyond our imagining, off the scale even by the standards of Tohoku.
The uneasiness I think we all feel since the Tohoku earthquake is a compound of many things, including the forcible realization that we’re living in geologic time, where catastrophic events capable of dwarfing our outposts of civilization do occur. The next massive eruption of Yellowstone isn’t likely, but it certainly isn’t impossible. It’s one of those things you worry about knowing you shouldn’t worry about it.
But I recognize the uneasiness from somewhere else. As we watch the specter of climate change unfold — trying to grasp the shifting, accelerating likelihoods — we’re looking at potential change of a kind normally associated with geologic time. It’s as though we’re running our own high-speed animation of atmospheric and climatic models over epochs — so much so that scientists seeking meaningful comparisons in temperature and atmospheric carbon concentrations look tens of millions of years before the Holocene, which includes all of historic time. Except that the atmospheric and climatic changes we’re looking at aren’t models. They’re real.
The Tohoku earthquake and tsunami were genuinely humbling, a reminder that we ride skimming on the surface of a volatile planet. But what’s the word for the emotion caused by knowing we’re contributing to the planet’s volatility? We run the risk of raising global average temperature at a rate faster than any time in the past 50 million years (5 degrees C by 2100). As ice masses melt and sea levels rise, the load on the Earth’s crust will change, with the likelihood of what is gingerly called “geospheric response” — i.e., more earthquakes and volcanoes. This is a subject only beginning to be understood by geologists.
A terrible uncertainty follows a major earthquake, an uncertainty we’ve always lived with. It dies down after a time, like the memory in Japan of the 1923 Great Kanto earthquake or the memory in this country of the San Francisco earthquake of 1906. But there’s a more terrible uncertainty in how we live and where we’re headed — the uneasy feeling that we’re entering geologic time in a way we’ve never known before.