Preconstructions of a Future Earth
Reconstructions and Preconstructions
What do we call an attempt not to reconstruct some past state of the Earth, but to exhibit likely future configurations of our homeworld? We could simply call this a prediction, but it is more fun to call it a “preconstruction,” analogous to “reconstructions” of the past. The preconstructions I am thinking of at the moment are attempts to arrive at what the Earth will look like hundreds of millions of years from now when plate tectonics has done its work on a large scale and all the continents of Earth are rearranged, both in their relationship to each other as well as in their relationship to Earth.
We all know that the surface of Earth consists of tectonic plates that float on magma, jostling each other, raising mountain ranges in the process, with the heavier plates being subducted under the lighter plates. The study of this jostling around of tectonic plates is called geomorphology. The vast liquid water oceans distinctive to Earth (at least within our solar system) outline the lighter plates that ride up higher, and which bear upon them that part of the terrestrial biosphere that consists of land-dwelling plants and animals. Over geological time, these lighter plates are sometimes brought together into one large mass, and sometimes they are separated. When they are brought together we call this a supercontinent, and the process of bringing together and separation is called the supercontinent cycle.
Given what we know about geomorphology and the supercontinent cycle, we can project that the forces that operate in the present will continue to operate in the future. This observation is the future parallel to the idea of uniformitarianism, usually applied only to the past, with the relevant slogan being the present is key to the past. As is turns out, the present is also key to the future. Future uniformitarianism implies that our presently separated continents, formerly united in a supercontinent we call Pangaea, will eventually be brought together into a future supercontinent. Several attempts at preconstructions of future supercontinents have been made, with notable attempts by Christopher Scotese, Roy Livermore, and Chris Hartnady, inter alia.
Non-constructive Reasoning in Geology and Geomorphology
I have observed many times that science is an inherently constructive endeavor, by which I mean that the methodologies of scientific reasoning are primarily constructivist in character. What makes preconstructions of a future Earth particularly interesting from a methodological standpoint is that these preconstructions are instances of non-constructive reasoning in geology, geomorphology, and plate tectonics. In other words, we can assert with confidence that the supercontinent cycle will continue, and this means that there will be a future supercontinent (and, over the longer horizon, several future supercontinents), but we cannot say exactly when this future supercontinent will form, where it will be located on the surface of Earth, or what exactly it will look like.
We know that the Earth will continue in existence, and that it will have future states, and we can even say something about these future states, but we cannot observe any of these future states, and we cannot (in a Kantian turn of phrase) exhibit any of them in intuition. How do we know these things? Our knowledge of the continuity of objects in existence forms part of the body of metaphysical presuppositions necessary to the practice of science, and so we “know” these things in a way distinct from the things we know by observing, measuring, quantifying, and recording. Nevertheless, science is impossible without accepting metaphysical presuppositions, so we meekly accept them and try to stay quiet about them because it is embarrassing for a scientist to try to answer questions of a metaphysical kind. In the past, we would have called this “faith.”
Today we have a naturalistic framework for understanding the metaphysical presuppositions of science, but the same dilemma of constructive vs. non-constructive thought was understood, though expressed differently, before science and naturalism took its modern form. John Donne wrote of the creation of the world, “That then this Beginning was, is a matter of faith, and so infallible. When it was, is a matter of Reason, and therefore various and perplex’d.” (Essays in Divinity) Just so, our attempts to constructively approximate non-constructively posited states-of-affairs remains various and perplex’d today.
Non-constructivity in Cosmology
The non-constructivity of predictions is not limited to geology, of course, so we could start thinking about other instances in science in which predictions of a certain kind are well established, but little else can be said about the prediction, except that the the prediction is largely non-constructive in nature. Insofar as science is all about prediction, science then is riddled through with non-constructive reasoning to an extent that I hadn’t previously realized. Cosmology, for example, is rich in predictions about the eventual structure and nature of the cosmos, but we know few if any details.
We know that our sun will eventually die, and that before it dies it will grow into a red giant star. Our sun is not large enough to result in a supernova, so the future red giant sun will go nova, and then settle down into a long future as a white dwarf. This is a schematic future history of our sun, but, because it is schematic, it lacks all detail, it is, in some sense, non-constructive knowledge about the future of our sun. We can say with some certainty what will happen, we can explain the causal mechanisms behind what will happen, and we can give approximate dates for what will happen to our sun, but beyond that we are saying that something will come to pass and that something will come to be, but little more is known.
If the preconstruction of the future history of our sun is schematic, the preconstruction of the future of the cosmos is known to us even less, as it involves the schematic future histories of billions of billions of stars over billions of billions of years (hat tip to Carl Sagan). The end of the Stelliferous Era, then, is many orders of magnitude less well known to us than the end of the life of our sun. We can say that star formation will eventually peter out, and then a long time after that the last stars will burn out and the universe will go dark (again). But what the Degenerate Era of cosmology will look like after the last stars burn out is something we posit without being able to observe or exhibit.
These preconstructions of a future cosmos are largely non-constructive. I think it is at least partially for this reason that cosmological eschatology (in so far as it exists as a discipline at all) is viewed with a great deal of suspicion. Nevertheless, the alternative is to deny future uniforimitarianism, which is to question the metaphysical presuppositions of science, which is to undermine science and the whole edifice of scientific knowledge. Which is the more painful: to undermine science, or to engage in the various and perplex’d work of cosmological eschatology?
The Next Supercontinent, and the Next after That
Between the next supercontinent that forms and the ultimate fate of the cosmos, there is still a lot of time that will be filled by not just the next supercontinent, but the next after that, and the next after that. If supercontinent cycles take about 500 million years from one supercontinent to the next, then there should be approximately two supercontinents on Earth each billion years. If Earth is about four and a half billion years old, and is about half way through its life span, then we could expect that there could be another eight to ten supercontinent cycles on Earth. However, in practical terms, it is much more complicated because the Earth is cooling, and we would expect that a cooling Earth would be less geologically active over time.
The Earth as we know it today, with its oceans and atmosphere and its verdant biosphere certainly won’t endure through another eight to ten supercontinent cycles. The sun will get hot enough to evaporate away the oceans, and I wonder if, on this desiccated world, the barren continents will continue to push each other around, reshaping a planet without any outlines of continents because there will be no oceans to outline them. At this point, the supercontinent cycle would resemble the task of Sisyphus, pointlessly rearranging the geosphere much as Sisyphus pointlessly pushed a boulder to the top of a hill, only to watch it roll to the bottom.
Because, as we have seen, much of our knowledge of the future is both uncertain and non-constructive, we cannot say at this time that a barren geomorphological process would be pointless. Perhaps in the distant future of Earth new forms of emergent complexity will arise that will be dependent upon geological processes. For example, something like consciousness emergent from a piezo electric effect taking place on a global scale could continue without a biosphere, and would be directly impacted by ongoing geomorphological processes. This is wildly speculative, but it cannot be ruled out as a possibility.