Thou must now at last perceive of what universe thou art a part, and of what administrator of the universe thy existence is an efflux, and that a limit of time is fixed for thee, which if thou dost not use for clearing away the clouds from thy mind, it will go and thou wilt go, and it will never return. (Marcus Aurelius, "Meditations")
You can't understand a man's actions if you don't take into account that what he does on a specific day is the result of events that took place during his whole lifetime and that will result in more events in the future. It is the same for a whole planet, although the lifespan of the Earth is much longer than that of a single human being. If we want to understand what's happening today on our planet, we must try to understand how it has changed over the eons to become what it his now and what it may become in the future.
That of looking at the whole span of the history of a whole planet or even of the whole universe has a special flavor; even though none of us will ever witness the ultimate end of our biosphere, still the idea that we can imagine it is a source of great fascination. And it is not something new: it is a whole field of human thought that we can call "eschatology", from the Greek world "eskhatos", meaning "the last".
In the history of people musing on the ultimate end of everything, we can see two lines of thought that we might dub, purely for convenience, the "Western" and the "Eastern" views. The Western view sees the universe, humans and everything, as having a finite and limited lifespan, the Eastern view sees the same concepts as an infinite series of cycles. The single cycle view is typical of thinkers steeped in the Greek-Latin tradition and of the monotheistic religions that arose around the Mediterranean area. In its basic form, the idea is that God created the world and that the world will have an end (apocalypse, from a Greek world meaning "revelation"). Human beings are supposed to live a one-time trial. You succeed or you don't, but God doesn't give you another chance. East-Asian thought seems to have been based on a different viewpoint: Buddhism sees the soul as forever reincarnating in new bodies. There is no end and no beginning to this endless cyucle that the wise may, however, be able to interrupt.
It is hard to say what factors created these two different schools of thought. One thing we know, however, is that today Western science can be seen as continuing the ancient tradition, that of the single cycle. For what we know, the universe appeared in a specific event called the "Big Bang" and it is destined to end, according to the most recent data, as a cold and dreary place made out of matter scattered over an immensely large volume. Back in 1956, Isaac Asimov was reasoning within this tradition when he wrote a story titled "The Last Question", where he imagined humankind engaged in a forever quest for how to reverse the cycle and rejuvenate the universe. But Asimov was also thinking outside the Western box when he proposed at the end that the question could be answered, although not by humans themselves but by the computer they had created. As there is nobody to tell the answer to, the computer proceeds to carry on the answer in practice by creating light and restarting the universe.
I must have read this old story by Isaac Asimov when I was, maybe, 15 years old and it inspired a post that I wrote on "Cassandra's Legacy" with the title "The Next Ten Billion Years" for which I borrowed from Asimov the same finale. This post of mine had a certain success and, recently, John Michael Greer ("The Archdruid") commented on it and produced his own version of the next ten billion years as he sees them. It is by all means a fascinating piece but different from mine in a deep philosophical sense. True to his role of druid, Greer explicitly rejects the Christian "one-cycle" tradition and leans on the multiple cycle view of the universe, for instance saying that, ten million years from now,
No fewer than 8,639 global civilizations have risen and fallen over the last ten million years, each with its own unique sciences, technologies, arts, literatures, philosophies, and ways of thinking about the cosmos.
and then he goes on to describe several non-human civilizations arising and disappearing in the span of several hundred million years, including one derived from raccoons, one from ravens, and one from freshwater clams. There is no evidence in Greer's vision of the entropy caused winding down of the universe. The atoms that once formed the Earth and its inhabitants are flung away in space by the last convulsion of the Sun and end up forming another star and a number of planets. The cycle restarts.
As I said, we are discussing philosophical matters and we'll never find an agreement on what the Earth will look like - say - ten million years from now. So, I'll just comment here on how science gives us very strong evidence for a "one-cycle" Earth. With that, I don't mean just an apocalyptic end of our planet when it will be finally consumed by an expanding Sun. No, the Earth has changed all the time over its four billion years of existence, it keeps changing, and the changes are profound and irreversible.
What we call the "biosphere" has been part of this great, long lasting cycle. As all things that are born and are destined to die, the biosphere must peak and decline. Actually, it has peaked and it is declining. The biosphere productivity over the past 3.5 billion years looks a little like a gigantic Hubbert peak according to a paper by Franck, Bounama and Von Bloh,
In a previous post, I wrote about this graph that:
As you see, the Earth's biosphere, Gaia, peaked with the start of the Phanerozoic age, about 500 million years ago. Afterwards, it declined. Of course, there is plenty of uncertainty in this kind of studies, but they are based on known facts about planetary homeostasis. We know that the sun's irradiation keeps increasing with time at a rate of around 1% every 100 million years. That should have resulted in the planet warming up, gradually, but the homeostatic mechanisms of the ecosphere have maintained approximately constant temperatures by gradually lowering the concentration of CO2 in the atmosphere. However, there is a limit: the CO2 concentration cannot go below the minimum level that makes photosynthesis possible; otherwise Gaia "dies".
So, at some moment in the future, planetary homeostasis will cease to be able to stabilize temperatures. When we reach that point, temperatures will start rising and, eventually, the earth will be sterilized. According to Franck et al., in about 600 million years from now the earth will have become too hot for multicellular creatures to exist.
Of course, the extinction of the biosphere is not for tomorrow or, at least, the calculations say so. But it is like estimating one's lifespan from statistical data. Theoretically, the homeostatic mechanisms that operate your body could keep you alive until reach a respectable age; sure, but homoeostasis is never perfect. For instance, there are mechanisms in your body designed to reverse the effects of traumas. You may expect these mechanisms to work well if you are young but, if you are hit by a truck at full speed, well, you end up on the wrong side of the life expectancy statistics.
Similar considerations apply to Gaia. Theoretically, the planetary homeostatic mechanisms should keep Gaia alive for hundreds of millions of years, but what about major perturbations, some planetary equivalent of being hit by a truck? Would Gaia be able to recover from a human caused runaway greenhouse catastrophe?
We cannot say for sure. What we can say is that we are living in a period called the "sixth extinction," similar to other major past extinctions. In most cases, these extinctions appear to have been caused by an increase in the concentration of greenhouse gases in the atmosphere. The sixth extinction, too, is taking place in correspondence to a rise of the concentration of carbon dioxide in the atmosphere that may never have happened so fast in the history of the planet. This rapid rise is also taking place under a solar irradiation that has never been so high as it is today. We can't rule out that the sixth extinction will be the last one.
So, as I said at the beginning, the present and the future of a single person can be understood from his or her past, and it is the same for the Earth (aka, "Gaia"). Science is telling us very, very strongly that the present moment is unique in the history of the planet: the future will not be like the past. It is true that, if we fail to survive as a civilization, there will be probably space for more human civilizations. And, if we go extinct, there may be space for the evolution of new sentient species. But all that will happen in different conditions and along a downward slope.
New human civilizations developing within the next few hundred thousand years will not have the coal and the fossil hydrocarbons that we have consumed today. In a few hundred million years from now, new sentient species might find oil that has reformed in shallow anoxic seas - but they won't have coal, the result of very special conditions occurring only once (for what we know) on this planet. And they will live in a planet with a much reduced biological productivity in comparison to ours. That doesn't mean that they won't be able to develop spaceflight, as Greer proposes - the future is full of opportunities, but it is never like the past.
In the end, these considerations give us just a hint of the sheer immensity of the future and of how difficult is the human attempt to conceive it. For what we know, we are a small ripple on the top of a gigantic tsunami wave that's crashing on some remote shore. As a ripple disappears, new ones appear, but the wave keeps rolling onward to its inevitable end. And yet, we know so little: there may be other shores, other waves, the universal sea may never stop to roll, and light and darkness may exchange places in a never ending dance. So, just as Asimov concluded his story, someday, the words "Let there be light" may be said again. And there will be light again.
So it can act as the mother
of all things.
Not knowing its real name
we only call it the Way
If it must be named,
let its name be Great.
Greatness means going on,
going on means going far,
and going far means turning back
(Tao Te King, as reported by Ursula K. Le Guin)