Tunguska Incident: Tuesday 30 June 1908
Part of a Series on the Philosophy of History
At about 7:17 AM local time on Tuesday 30 June 1908–117 years ago today — an enormous explosion occurred in Siberia at Tunguska. Some people refer to the 30th of June as “Asteroid Day” as a kind of commemoration of the Tunguska incident. There are many contemporaneous accounts of the blast and its immediate after effects. The explosion occurred when Russia was still ruled by the Tsar, but the first scientific expedition to the site wasn’t until almost twenty years later, in 1927, when a scientific team led by Leonid Kulik, under the auspices of the Soviet Academy of Sciences, investigated the site and found no impact crater. Instead, the forest immediately at the blast site was scorched but still standing, like telegraph poles stripped of all their branches (and which for that reason was dubbed the “telegraph pole forest”), while further out from the blast sight trees had been flattened in a radial pattern away from the blast site over hundreds of square miles. Given the evidence that was observed, the best explanation was the air burst of a meteor about 5–10 km above the surface, with the blast yielding the equivalent of several megatons of TNT.
Many have noted in retrospect that if the blast had occurred over a city, it would have destroyed even a large city as effectively as a nuclear blast. As a counterfactual it’s interesting to consider what the effects on subsequent history would have been had a city been destroyed on 30 June 1908 — this at a time before the world wars of the twentieth century, which made the sudden destruction of cities all-too-familiar. How would humanity of more than a century ago tried to understand the sudden annihilation of a city? Fortunately we’ll never know the answer in this particular case. The blast occurred in a trackless wilderness that took almost twenty years to reach, but even being remote the magnitude of the blast has been the occasion for speculation ever since.
More significantly, the Tunguska event is a reminder of the ongoing interaction between Earth and its cosmological environment. We tend to think of the solar system as though it were finished and settled, but it isn’t. While collisions between bodies in the solar system have become less frequent over time, collisions still do occur. More than a hundred years after Tunguska, on 15 February 2013, Russia experienced another meteor airburst at Chelyabinsk in the Urals. This was much smaller than the Tunguska airburst, and caused far less damage, but it was a reminder of our vulnerability, and of the fact that Russia covers so much of Earth’s surface that when a meteor comes down, it’s likely to land in Russia.
Earth isn’t the only astronomical body in space involved in collisions with other astronomical bodies. On 18 June 1178 Five English monks at Canterbury witnessed what may have been a major impact on the moon. There are other possible explanations for what they saw almost exactly 847 years ago, but all you have to do is look at the moon to know that it’s been hit many times since it formed. So even though recorded history is a very short period of time in comparison to cosmological time, we have been continuously reminded throughout our history that Earth is part of a larger cosmos that announces itself to us through events that only eyewitnesses believe.
For most of our history we didn’t know how to interpret much of the evidence of Earth’s place in the universe, and to underline this there’s an apocryphal story that Thomas Jefferson was claimed to have said of the Weston meteorite fall on 14 December 1807, “Gentlemen, I would rather believe that two Yankee professors would lie than believe that stones fall from heaven.” Jefferson didn’t actually say this, but Benjamin Stillman, the son of one of the two Yale professors in question, who attributed this remark to Jefferson, was riffing off David Hume’s famous “Of Miracles” chapter in his An Enquiry Concerning Human Understanding. Hume had written:
“…the knavery and folly of men are such common phenomena that I should rather believe the most extraordinary events to arise from their concurrence than admit of so signal a violation of the laws of nature.”
If a city had been destroyed by the Tunguska blast that certainly would have been understood by many to be a signal violation of the laws of nature, though what it really would have pointed toward rather is the inadequacy of our understanding of nature at that time.
We aren’t isolated from the universe, but part of it. Being part of the universe means that there is a continuous exchange of matter between bodies in the solar system. Asteroid collisions sometimes blast surface materials off one planet and send them into interplanetary space, where they eventually may in turn fall into the gravity well of some planet or other object. This might happen in months or years, but it also might take millions of years for the materials blasted off the surface of one world to land on another. It’s been said half-jokingly, but also half seriously, that there could be dinosaur bones on the moon, blasted off Earth 66 million years ago, and indeed there could still be dinosaur bones orbiting in the solar system, having been blasted off the surface of Earth and never having landed anywhere.
Probably the most famous impact on Earth was the far greater impact about 66 million years ago that led to the extinction of the dinosaurs (the Chicxulub impactor). Sometimes this is called the K-Pg impactor, designated by the geological ages that it separates, the Cretaceous period and Paleogene period. It used to be called the K-T boundary, before the name of the Tertiary period was changed to the Paleogene by the International Commission on Stratigraphy. This collision has particular relevance for human beings, apart from jokes about dinosaur bones on the moon, since the impact also marked the beginning of the Cenozoic Era, which is the Era of mammalian dominance. It’s likely that we wouldn’t have evolved if the dinosaurs hadn’t been the victims of the K-Pg impact, allowing for the adaptive radiation of mammals, who went on to fill all the ecological niches formerly occupied by dinosaurs.
An impact doesn’t even need to impact on Earth for it to affect the terrestrial biosphere. An extraterrestrial impact in the solar system, but not on the surface of Earth, could spread dust in the inner solar system, shading us a little bit, which would cause a decline in solar insolation, and thus a drop in temperature. There is at least one paper that has argued that the Late Ordovician Mass Extinction, about 445 million years ago (which can be abbreviated as LOME), was caused by an event like this. Not exactly an extraterrestrial collision between astronomical bodies in the vicinity of Earth, but rather the breakup of an asteroid in the asteroid belt. In “An extraterrestrial trigger for the mid-Ordovician ice age: Dust from the breakup of the L-chondrite parent body,”by Birger Schmitz and many others, we find this:
“Our revised ‘astrogeobiological’ explanation for the conspicuous faunal diversifications observed in the mid-Ordovician involves breakup of an ~150-km large asteroid in the asteroid belt, which flooded the inner solar system with dust. The sudden global change from an equable greenhouse situation to a climatically more heterogeneous icehouse world spurred the GOBE.” (“GOBE” is an acronym for “Great Ordovician Biodiversification Event”)
And other more recent paper, “Evidence suggesting that earth had a ring in the Ordovician,” by Andrew G. Tomkins, Erin L. Martin, and Peter A. Cawood, builds on the idea of the Ordovician ice age having an extraterrestrial cause:
“…we suggest that a debris ring formed after this break up event, from which material deorbited to produce the observed crater distribution. We further speculate that shading of Earth by this ring may have triggered cooling into the Hirnantian global icehouse period.”
Events like this, while large on a human scale, are still local events within our solar system. Terrestrial history could also be shaped by larger events, what we could call cosmological scale events. Another paper has argued that distant supernovae could have been the cause of the end-Devonian extinction about 360 million years ago. In “Supernova triggers for end-Devonian extinctions” by Brian D. Fields, Adrian L. Melott, John Ellis, and Brian C. Thomas wrote:
“We… propose that the end-Devonian extinctions were triggered by supernova explosions at ∼20 pc, somewhat beyond the ‘kill distance’ that would have precipitated a full mass extinction.”
At an even larger scale, it has been hypothesized that gamma ray bursts can cause mass extinctions. The Fields paper I just quoted focuses on cosmic rays, but gamma ray bursts are another danger of extremely energetic astrophysical events. Gamma ray bursts on the largest scale have been proposed as an explanation for the Fermi paradox, or why we seem to be alone in the universe because we can’t detect any SETI messages. A gamma ray burst could be so powerful that it could sterilize large sections of any galaxy populated with life. If a big gamma ray burst were to happen every few hundred million years, that would be enough to keep life from getting complex enough to send us a SETI message. This is mass extinction on a cosmological scale.
We obviously don’t have any evidence for this, other than the evidence of silence, i.e., the absence of evidence that isn’t evidence of absence, but mass extinctions on Earth may be explained in part by cosmological forces. Since mass extinctions are difficult to explain, many hypotheses have been proposed to account for them, including extraterrestrial mechanisms like supernovae. And mass extinctions teach us something important, such as that entire taxonomic clades can be wiped out by a sufficiently large event, leading to what ecologists call a regime shift. The extinction of the dinosaurs was at the same time a regime shift from a dinosaur regime to mammalian regime.
Even events less catastrophic than mass extinctions can teach us something, as, for example, with the extinction of the passenger pigeon. During the 19th century the passenger pigeon used to pass overhead in North America in flocks bigger than a million birds, so this wasn’t a population that was in decline over a long period of time. Sometimes a population can crash all the way to extinction after having been common in the recent past. Since this is something most of us don’t want to happen to human beings, we should pay attention to extinctions, but to make this obvious observation is a paradigmatically naturalistic claim about the human species, namely, that we are a biological species, we are subject to the same biological and ecological forces that every other species on the planet is subject, and we are vulnerable to extinction, as is every other species in the biosphere. Our intelligence and our language and our technology don’t exempt us from this vulnerability, and many have argued that out intelligence makes us more likely to go extinct due to existential risks by our own hand, as it were, like nuclear war or the gray goo scenario.
Not only are we vulnerable to extinction, we know that the average mammalian species only lasts about one or two million years. Unless we become a so-called living fossil like the coelacanth, our kind will be extinct in a few million years at most. You can see the rapid churning of mammalian species at the John Day fossil beds in central Oregon, which don’t have dinosaurs in them because they’re mostly from the past several million years, but there are a lot of mammalian species that once flourished in central Oregon. At the little museum for the fossil beds near Mitchell, OR, there are some wonderful skulls of miniature sabre-toothed tigers and a number of other mammal species no longer in existence. If you ever come to Oregon I recommend a visit there.
When Darwin first proposed descent with modification, and natural selection as the mechanism for speciation, there were many who looked around the familiar world and couldn’t find any “transitional” forms. I always find this rather humorous when I think of it, since everything in the biosphere is a transitional form between the species from which it descended and the species of which it is the ancestor, which the sole exception of species that go extinct leaving no successor species. That is to say, the only non-transitional species are those that are dead species walking.
Likely every other species in the biosphere, we are a transitional species. Nietzsche showed that he understood when he wrote in Thus Spake Zarathustra,
“Man is a rope stretched between the animal and the Superman — a rope over an abyss. A dangerous crossing, a dangerous wayfaring, a dangerous looking-back, a dangerous trembling and halting. What is great in man is that he is a bridge and not a goal.”
Nietzsche’s meaning was moral, not biological, but however we construe the transitional nature of human being, human history is but a stage in a larger history. I take it to be a fundamental principle of naturalistic philosophy of history that human history is nested within natural history. One implication of this is that human history is shaped by natural history, at least to some extent. To what extent we may differ, but human history is falsified if we attempt to treat it in isolation from natural history. Brian D. Fields, one of the authors in the last paper I quoted, has said:
“The overarching message of our study is that life on Earth does not exist in isolation… We are citizens of a larger cosmos, and the cosmos intervenes in our lives — often imperceptibly, but sometimes ferociously.”
In other words, we are part of natural history, and not exempted from it. Our ancestors survived all past mass extinctions and collisions with astronomical bodies, or we wouldn’t be here. And we are subject to future mass extinctions and collisions that could permanently and drastically alter the biosphere, or even result in our extinction. So we’re vulnerable to cosmological events, both local events that occur only within our solar system or which exclusively affect Earth, as well as larger scale events that can shape the history of life over an entire galaxy.
Let’s consider another example that I haven’t yet mentioned. Almost fifty years before the Tunguska event, on the first and second of September, 1859, there was what we now call the Carrington event, which was an intense geomagnetic storm, probably caused by a coronal mass ejection from the sun, which caused sparking and fires on some telegraph lines, and also made it possible to send telegraphic messages without using a power source, relying on the auroral current alone. A geomagnetic storm of this magnitude today, with our far greater reliance on electrical systems, would probably be catastrophic, but its damage in 1859 was minimal. Events like this can shape and have shaped human history, and there’s a sense in which we can say that our history has been so profoundly shaped by natural history there would have been no human history without catastrophic natural events, because we wouldn’t exist if it weren’t for the K-Pg impact and the extinction of the dinosaurs.
These kinds of vulnerability are now called existential risks, though existential risks are defined broadly to include both natural events and human events, and in some cases we can’t make a clear distinction between the two, because human beings act as a force of nature. We could say that the Carrington event intersected with human history at a particular stage in our development, and it had the limited the consequences that it had both because of the relative intensity of the event and the relative level of technological development of humanity at the time. It’s like two forces of natural colliding. The largely agricultural civilization still intact in 1859 was resilient in the face of geomagnetic storms, while our industrialized civilization would be much less robust, and could potentially be crippled by a large coronal mass ejection. A Carrington event could be an existential risk for an industrialized civilization that makes extensive use of electrical technologies, but it will leave both agricultural civilizations and nomadic hunter-gatherers untouched.
We see, then, that not all human history is alike subject to extraterrestrial existential risks. Arguably, if we wanted to proof civilization against catastrophe, we could turn the clock back and return to the horse-and-buggy days. Alternatively, we can see events like the Carrington event or the Tunguska event as signs that we need to accelerate our technological development so that we can make the most of our window of opportunity while it presents itself. It is entirely possible that in the prior thirteen billion years and some, no other species has come so far in technological development before being crippled or destroyed by some cosmological catastrophe. Civilizations may be as vulnerable as mortal man:
Man that is born of a woman is of few days, and full of trouble. He cometh forth like a flower, and is cut down: he fleeth also as a shadow, and continueth not.
If we press our advantage, we may become a multi-planetary species and then our eggs won’t all be in one basket (the Earth). If we become multi-planetary we will have insulated ourselves from some existential risks, but certainly not all of them, as we’ve seen that some existential risks are cosmological in scope and scale. And there’s no guarantee that our future history as a multi-planetary species will be any longer than our history on Earth alone, not to mention that there’s no guarantee of humanity’s spiritual evolution under either scenario, which is what concerned Nietzsche in Thus Spake Zarathustra. But the question of two paths to different human futures is only relevant if human beings can take control of our own history, which was the concern of that arch-rationalist Husserl, who was as different from Nietzsche as any philosopher could be, and who therefore saw the large scale history of humanity differently.
We’ve all heard that there is a proposal to call the current geological epoch the Anthropocene. This convention was rejected last year by the International Commission on Stratigraphy, the same official body I mentioned earlier that re-named the Tertiary as the Paleogene. Despite its rejection, the idea persists and will continue to persist as human powers grow. Discussions of the Anthropocene usually center on human impacts to the biosphere that follow from increasing human powers, and usually not to the credit of that influence. In other words, the idea of the Anthropocene is often employed as a cudgel against industrialized civilization, although almost no one goes so far as to endorse the scenario I just suggested of turning back the clock to the horse-and-buggy days.
But we can provide a very different valuation of the Anthropocene if we look at matters a bit differently. Insofar as the advent of the Anthropocene is coupled to growing human powers over the natural environment, as long as this development continues we may someday be able to assert control over existential risks, managing them rather than merely fearing them. And we may someday cross the threshold of being able to shape our own history rather than having it shaped for us by natural forces. To a certain extent, these two thresholds coincide: if we can manage existential risks, we can at least make provisions for our survival as a species. If we want to pursue a Nietzsche revaluation of all values, we can revalue the Anthropocene as the beginning of an era in which human history is consciously and deliberately made by human beings. If and when we cross that threshold, it will mark a new era of human history, and, if we like, we can call that new era of human history the Anthropocene.
