Third Time’s a Charm
8 February 2014
The Three Eras of Life on Earth
The Earth, it would seem, has been regularly reduced to biological penury throughout its long history, which has been punctuated by mass extinctions that have very nearly reduced biodiversity to zero. It is possible that, in the earliest history of life on Earth, when our planet was regularly bombarded by objects from space, and exposed to especially harsh conditions, life may have emerged multiple times, only to be wiped out again in short order. There would have been plenty of time for this to occur during the 550 million years prior to the emergence of the earliest life known to be continuous with our own.
The repeated denudation of the planet by mass extinctions constituted a kind of ecological succession on a grand scale. Each time life had to recover anew, and, in recovering, the surviving species (the “weeds” that were the most robust and which went on to colonize the denuded landscape and seascape) underwent dramatic periods of adaptive radiation until, in the global climax ecosystems prior to a mass extinction event, almost every niche for life has been filled — possibly several times over, leading to contested niches where multiple species compete for the same limited resources.
The history of life is such a reliable indicator of geological time that there is an entire discipline — biostratigraphy — given over to the dating of rocks by the fossils they contain. Once life becomes sufficiently complex to leave a record of itself in the rocks of our planet, the development of life is a sure guide to the age of the rocks that contain traces of this past life. Contemporary scientific geology largely got its start through biostratigraphy in the work of William Smith (called “strata Smith” by his contemporaries), whom I have previously mentioned in The Transplanetary Perspective.
Three of the major divisions of geological time are named for the eras of life that they comprise: Paleozoic (old life), Mesozoic (middle life), and Cenozoic (common, or recent, life). These divisions of geological time give a “big picture” view of the history of life on Earth. The mass extinction events at the end of the Permian and at the K-T boundary were so catastrophic that the Earth in the case of the end Permian extinction came perilously close to being sterilized, and while the K-T event (now known as the Cretaceous–Paleogene or K–Pg extinction event) was not as disastrous, it ended the dominion of the dinosaurs over most ecological niches and thereby gave mammals the opportunity to experience an explosive adaptive radiation.
Million Year Old Civilizations
We know that intelligent life on Earth arose in the late Cenozoic era, but how clement were these earlier eras of life on Earth to intelligent life? If intelligent life had arisen in the Paleozoic, founded a civilization, and survived to the present, that civilization would be in excess of 250 million years old. If, again, intelligent life had arisen in the Mesozoic, founded a civilization, and survived to the present, that civilization would be in excess of 65 million years old. However, both of these counterfactual civilizations that did not happen would have almost certainly have been destroyed by the catastrophic mass extinctions that separated these eras of terrestrial life (unless they had taken adequate measures to mitigate existential risk, which would seem to be a necessary condition for any truly long-lived civilization).
The idea of a civilization a million or more years old was a theme discussed by Carl Sagan on several occasions. Here is an explicit formulation of the million-year-old civilization theme from Chapter XII, “Encyclopedia Galacitca,” from Sagan’s book Cosmos:
“What does it mean for a civilization to be a million years old? We have had radio telescopes and spaceships for a few decades; our technical civilization is a few hundred years old, scientific ideas of a modern cast a few thousand, civilization in general a few tens of thousands of years; human beings evolved on this planet only a few million years ago. At anything like our present rate of technical progress, an advanced civilization millions of years old is as much beyond us as we are beyond a bush baby or a macaque. Would we even recognize its presence? Would a society a million years in advance of us be interested in colonization or interstellar spaceflight? People have a finite lifespan for a reason. Enormous progress in the biological and medical sciences might uncover that reason and lead to suitable remedies. Could it be that we are so interested in spaceflight because it is a way of perpetuating ourselves beyond our own lifetimes? Might a civilization composed of essentially immortal beings consider interstellar exploration fundamentally childish?”
Carl Sagan, Cosmos, Chapter XII, “Encyclopaedia Galactica”
Human civilization could be considered as being more than ten thousand years old if we date the advent of civilization to the Neolithic Agricultural Revolution. This is an atypical way to think about civilization, but I have seen it in a few sources (Jacob Bronowski, I think, takes this view, more or less), and it is how I myself think about civilization. A civilization ten thousand years old or more is nothing to dismiss; persisting for ten thousand years is a non-trivial accomplishment. Yet the history of terrestrial civilization may be compared to the history of terrestrial life: there is a long period that is nearly stagnant, with painfully slow innovations, and then an event occurs — the Cambrian explosion for life, the industrial revolution for civilization — and what it means to be “alive” or “civilized” is radically altered.
Dating to the Neolithic Agricultural revolution is consistent with my recent suggestion in From Biocentric Civilization to Post-biological Post-Civilization that civilization could be minimally defined as a coevolutionary cohort of species. However, our industrial-technological civilization is barely more than two hundred years old. To consider the geologically insignificant period of time of one hundred years is to contemplate a period of time half again as long as the entire history of industrial-technological civilization. The kind of technological gains that industrial-technological civilization could experience over a period of a hundred years can be quite remarkable, as our experience of the past hundred years suggests.
This year, 2014, we experience the one hundred year anniversary of global industrialized warfare. Not long after, we will experience the hundred year anniversaries of digital computers, jet propulsion, rocketry, and nuclear technology. Some of these technologies have improved by orders of magnitude. Some have improved very little. If the coming century brings commensurate technological innovations (not to mention innovations in science that would drive these technological innovations), even if not all these developments experience exponential development, and many languish in a state of stagnation, our world and our understanding of the world will nevertheless be repeatedly revolutionized.
Given what we know about the rapidity of technological change — bequeathed to our industrial-technological civilization as a consequence of the STEM cycle — we ought to conclude that we can know almost nothing about what a million year civilization would be like, except in so far as we might be able to imagine only the most stagnant aspects of such a civilization. It would be beyond our ability to understand advanced technologies ten thousand years hence, just as our ancestors, only beginning to lay the foundations of agrarian-ecclesiastical civilization ten thousand years ago, could have understood our advanced technologies today. Understanding across these orders of developmental magnitude lie beyond the human zone of proximal development.
I have written previously that there is an earliest bound in the history of our universe for life, for intelligent life, and for civilization. It would not be possible to produce an industrial-technological civilization as we know it (i.e., a peer civilization) without heavier metallic elements, so that the emergence of industrial-technological civilization must minimally wait for the formation of Population I stars and their planetary systems. That being said, many population I stars have been around for billions of years, and there have consequently been billions of years for industrial-technological civilizations to emerge and to attain great age.
Are there other constraints upon the emergence of life, intelligence, and civilization that move the boundary for the earliest possible emergence of these phenomena nearer to the present? Is there any reason to suppose, from our knowledge of the natural history of Earth and the complexity of the human brain, that intelligent life and civilization could not have arisen in earlier eras of life — Paleozoic intelligent life or Mesozoic intelligent life, which would, in turn, according to Civilization-Intelligence Covariance, give rise to Paleozoic civilization or Mesozoic civilization? Or, if not here on Earth, why not some other planet orbiting a population I star where life begins 550 million years after the formation of the planet?
Octopi, cuttlefish, and other cephalopods with large brains and highly sophisticated nervous systems — it takes a lot of raw neural processing power to do what some cephalopods do with their skin color — would seem to be ideal candidates for early terrestrial intelligent life. Octopi date back to the Devonian Period, more than 360 million years ago, during the Paleolithic Era, so that ancestors of this life form survived both the End Permian extinction and the K-T extinction (cf. Fossil Octopuses). Why didn’t cephalopods establish a counterfactual civilization during the Permian? There was certainly time enough to do so before the End Permian extinction.
Is a backbone, or something that can serve a similar function like an exoskeleton, a necessary condition for intelligence to issue in the production of civilization? Multicellular life forms without a backbone, or confined to an aquatic environment, might well develop intelligence, but would have a difficult time building a technological civilization — difficult, but not impossible. This is a question I considered previously in The Place of Bilaterial Symmetry in the History of Life and Counterfactuals Implicit in Naturalism.
If we should find life in the oceans below the icy surface of Europa, or any of the other moons in our solar system internally heated by gravitational forces, it would consist of life forms peculiarly constrained by their environment, i.e., possibly more constrained than terrestrial conditions, and therefore more likely to favor extremophiles. Oceanic lifeforms beneath a crust of ice many kilometers thick would not only have the technological disadvantage faced by any intelligent aquatic species, but would face the additional disadvantage of being cut off from the stars. Unable to physically see their place in the universe, such lifeforms might have an even more difficult time that we had in coming to understand the world. The mythology of such a life form would have to be very different from the mythologies created by early human societies, in which the stars typically played a prominent role. Any civilization that might be conjoined with such a mythology might constitute an extremophile civilization.
Inside the Charmed Circle
Many of the questions that I have posed above are variations on ancient themes of anthropocentrism, and from within the charmed circle of anthropocentrism it is difficult for us to see outside that circle. Our minds are quite literally defined by that circle, being the product of human biology, and our imagination is largely circumscribed by the limitations of our minds. But our minds are also capable, with effort, of passing beyond the charmed circle of anthropocentrism, identifying anthropic bias as such and transcending it.
For us, the third time life got a chance on Earth was the charm. Paleozoic life came and (largely) went without producing intelligence or civilization, as did Mesozoic life. It was not until Cenozoic life that intelligence and civilization emerged. But was this the result of mere contingency, or a function of some operative constraint — possibly even a constraint no one has even noticed because of its pervasive presence — that prevented intelligence and civilization from arising in earlier geological eras?
While there might be reason to believe that other forms of life will have something like a DNA structure, or that something like the transition from prokaryotic cells to eukaryotic cells will have taken place, but there is no particular reason to believe that the large scale structure of life on other worlds would have the terrestrial tripartite structure, since this big picture view of life on Earth was a result of particular mass extinction events that seem too contingent to characterize any possible emergence of life. However, there is reason to believe that there will be some mass extinction events afflicting life on other worlds, and at least some of these mass extinction events will result from large scale cosmological events. If solar systems form elsewhere in a process like the formation of our solar system, life elsewhere would also be exposed to asteroid impacts, comets, solar flares, and the like. This is one of the lessons of astrobiology.
That there will be constraints and contingencies that bear upon life we can be certain; but we cannot (yet) know exactly what these constraints and contingencies will be. This is a non-constructive observation: invoking the existence of constraints and contingencies without saying what they will be. What would a constructive approach to life’s constraints and contingencies look like? Is it necessary to adopt a non-constructive perspective where our knowledge is so lacking? As knowledge of the conditions of astrobiology and astrocivilization grows, may we yet adopt a constructive conception of them?
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