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biosphere 0

In Rational Reconstructions of Time I noted that stellar evolution takes place on a scale of time many orders of magnitude greater than the human scale of time, but that we are able to reconstruct stellar evolution by looking into the cosmos and, among the billions of stars we can see, picking out examples of stars in various stages of their evolution and sequencing these stages in a kind of astrophysical seriation. Similarly, the geology of Earth takes place on a scale of time many orders of magnitude removed from human scales of time, but we have been able to reconstruct the history of our planet through a careful study of those traces of evidence not wiped away by subsequent geological processes. Moreover, our growing knowledge of exoplanetary systems is providing a context in which the geological history of Earth can be understood. We are a long way from understanding planet formation and development, but we know much more than we did prior to exoplanet discoveries.

The evolution of a biosphere, like the evolution of stars, takes place at a scale of time many orders of magnitude beyond the human scale of time, and, as with stellar evolution, it is only relatively recently that human beings have been able to reconstruct the history of the biosphere of their homeworld. This began with the emergence of scientific geology in the eighteenth century with the work of James Hutton, and accelerated considerably with the nineteenth century work of Charles Lyell. Scientific paleontology, starting with Cuvier, also contributed significantly to understanding the natural history of the biosphere. A more detailed understanding of biosphere evolution has begun to emerge with the systematic application of the methods of scientific historiography. The use of varve chronology for dating annual glacial deposits, dendrochronology, and the Blytt–Sernander system for dating the layers in peat bogs, date to the late nineteenth century; carbon-14 dating, and other methods based on nuclear science, date to the middle of the twentieth century. The study of ice cores from Antarctica has proved to be especially valuable in reconstruction past climatology and atmosphere composition.

The only way to understand biospheric evolution is through the reconstruction of that evolution on the basis of evidence available to us in the present. This includes the reconstruction of past geology, climatology, oceanography, etc. — all Earth “systems,” as it were — which, together with life, constitute the biosphere. We have been able to reconstruct the history of life on Earth not from fossils alone, but from the structure of our genome, which carries within itself a history. This genetic historiography has pushed back the history of the origins of life through molecular phylogeny to the very earliest living organisms on Earth. For example, in July 2016 Nature Microbiology published “The physiology and habitat of the last universal common ancestor” by Madeline C. Weiss, Filipa L. Sousa, Natalia Mrnjavac, Sinje Neukirchen, Mayo Roettger, Shijulal Nelson-Sathi, and William F. Martin (cf. the popular exposition “LUCA, the Ancestor of All Life on Earth: A new genetic analysis points to hydrothermal vents as the planet’s first habitat” by Dirk Schulze-Makuch; also We’ve been wrong about the origins of life for 90 years by Arunas L. Radzvilavicius) showing that recent work in molecular phylogeny points to ocean floor hydrothermal vents as the likely point of origin for life on Earth.

This earliest history of life on Earth — that terrestrial life that is the most different from life as we know it today — is of great interest to us in reconstructing the history of the biosphere. If life began on Earth from a single hydrothermal vent at the bottom of an ocean, life would have spread outward from that point, the biosphere spreading and also thickening as it worked its way down in the lithosphere and as it eventually floated free in the atmosphere. If, on the other hand, life originated in an Oparin ocean, or on the surface of the land, or in something like Darwin’s “warm little pond” (an idea which might be extended to tidepools and shallows), the process by which the biosphere spread to assume its present form of “planetary scale life” (a phrase employed by David Grinspoon) would be different in each case. If the evolution of planetary scale life is indeed different in each case, it is entirely possible that life on Earth is an outlier not because it is the only life in the universe (the rare Earth hypothesis), but because life of Earth may have arisen by a distinct process, or attained planetary scale by a distinct mechanism, not to be found among other living worlds in the cosmos. We simply do not know at present.

Once life originated at some particular point on Earth’s surface, or deep in the oceans, and it expanded to become planetary scale life, there seems to have been a period of time when life consisted primarily of horizontal gene transfer (a synchronic mechanism of life, as it were), before the mechanisms of species individuation with vertical gene transfer and descent with modification (a diachronic mechanism of life). It is now thought the the last universal common ancestor (LUCA) will only be able to be traced back to this moment of transition in the history of life, but this is an area of active research, and we simply do not yet know how it will play out. But if we could visit many different worlds in the earliest stages of the formation of their respective biospheres, we would be able to track this transition, which may occur differently in different biospheres. Or it may not occur at all, and a given biosphere might remain at the level of microbial life, experiencing little or no further development of emergent complexity, until it ceased to be habitable.

While we can be confident that later emergent complexities must wait for earlier emergent complexities to emerge first, no other biosphere is going to experience the same stages of development as Earth’s biosphere, because the development of the biosphere is a function of a confluence of contingent circumstances. The history of a biosphere is the unique fingerprint of life upon its homeworld. Any other planet will have different gravity, different albedo, different axial tilt, axial precession, orbital eccentricity, and orbital precession, and I have explained elsewhere how these cycles function as speciation pumps. The history of life on Earth has also been shaped by catastrophic events like extraterrestrial impacts and episodes of supervolcano eruptions. It was for reasons such as this that Stephen J. Gould said that life on Earth as we know it is, “…the result of a series of highly contingent events that would not happen again if we could rewind the tape.”

Understanding Earth’s biosphere — the particularities of its origins and the sequence of its development — is only the tip of the iceberg of reconstructing biospheres. Ultimately we will need to understand Earth’s biosphere in the context of any possible biosphere, and to do this we will need to understand the different possibilities for the origins of life and for possible sequences of development. There may be several classes of world constituted exclusively with life in the form of microbial mats. Suggestive of this, Abel Mendez wrote on Twitter, “A habitable planet for microbial life is not necessarily habitable too for complex life such as plants and animals.” I responded to this with, “Eventually we will have a taxonomy of biospheres that will distinguish exclusively microbial worlds from others…” And our taxonomy of biospheres will have to go far beyond this, mapping out typical sequences of development from the origins of life to the emergence of intelligence and civilization, when life begins to take control of its own destiny. On our planet, we call this transition the Anthropocene, but we can see from placing the idea in this astrobiological context that the Anthropocene is a kind of threshold event that could have its parallel in any biosphere productive of an intelligent species that becomes the progenitor of a civilization. Thus planetary scale life is, in the case of the Anthropocene, followed by planetary scale intelligence and planetary scale civilization.

levels of biological organization

Ultimately, our taxonomy of the biosphere must transcend the biosphere and consider circumstellar habitable zones (CHZ) and galactic habitable zones (GHZ). In present biological thought, the biosphere is the top level of biological organization; in astrobiological thought, we must become accustomed to yet higher levels of biological organization. We do not yet know if there has been an exchange of life between the bodies of our planetary system (this has been posited, but not yet proved), in the form of lithopanspermia, but whether or not it is instantiated here, it is likely instantiated in some planetary system somewhere in the cosmos, and in such planetary systems the top level of biological organization will be interplanetary. We can go beyond this as well, positing the possibility of an interstellar level of biological organization, whether by lithopanspermia or by some other mechanism (which could include the technological mechanism of a spacefaring civilization; starships may prove to be the ultimate sweepstakes dispersion vector). Given the possibility of multiple distinct interplanetary and interstellar levels of biological organization, we may be able to formulate taxonomies of CHZs for various planetary systems and GHZs for various galaxies.

One can imagine some future interstellar probe that, upon arrival at a planetary system, or at a planet known to possess a biosphere (something we would know long before we arrived), would immediately gather as many microorganisms as possible, perhaps simply by sampling the atmosphere or oceans, and then run the genetic code of these organisms through an onboard supercomputer, and, within hours, or at most days, of arrival, much of the history of the biosphere of that planet would be known through molecular phylogeny. A full understanding of the biospheric evolution (or CHZ evolution) would have to await coring samples from the lithosphere and cryosphere of the planet or planets, and, but the time we have the technology to organize such an endeavor, this may be possible as well. At an ever further future reach of technology, an intergalactic probe arriving at another galaxy might disperse further probes to scatter throughout the galaxy in order to determine if there is any galactic level biological organization.

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Thursday


'Io is the most volcanically active body in the solar system. At 2,263 miles in diameter, it is slightly larger than Earth’s moon.' (NASA)

“Io is the most volcanically active body in the solar system. At 2,263 miles in diameter, it is slightly larger than Earth’s moon.” (NASA)

In earlier posts of this series on Civilizations of Planetary Endemism we saw that planets not only constitute a “Goldilocks” zone for liquid water, but also for energy flows consistent with life as we know it. I would like to go into this in a little more detail, as there is much to be said on this. It is entirely possible that energy flows on a planet or moon outside the circumstellar habitable zone (CHZ) could produce sufficient heat to allow for the presence of liquid water in the outer reaches of a planetary system. Indeed, it may be misleading to think of habitable zones (for life as we know it) primarily in terms of the availability of liquid water; it might be preferable to conceive a habitable zone primarily in terms of regions of optimal energy flow (i.e., optimal for life as we know it), and to understand the availability of liquid water as a consequence of optimal energy flow.

Our conception of habitability, despite what we already know, and what we can derive from plausible projections of scientific knowledge, is being boxed in by the common conceptions (and misconceptions) of biospheres and CHZs. We can posit the possibility of “oasis” civilizations on worlds where only a limited portion of the surface is inhabitable and no “biosphere” develops, although enough of a fragment of a biosphere develops in order for complex life, intelligence, and civilization to emerge. We do not yet have an accurate term for the living envelope that can emerge on a planetary surface, but which does not necessary cover the entire planetary surface. I have experimented with a variety of terms to describe this previously. For example, I used “biospace” in my 2011 presentation “The Moral Imperative of Human Spaceflight,” but this is still dissatisfying.

As is so often the case, we run into problems when we attempt to extrapolate Earth sciences formulated for the explicit purpose of accounting for contingent terrestrial facts, and never conceived as a purely general scientific exercise applicable to any comparable phenomena anywhere in the universe. This is especially true of ecology, and since I find myself employing ecological concepts so frequently, I often feel the want of such formulations. Ecology as a science is theoretically weak (it is much stronger on its observational side, which goes back to traditional nature studies that predate ecology), and its chaos of criss-crossing classification systems reflects this.

There are a great many terms for subdivisions of the biosphere — ecozone, bioregion, ecoregion, life zone, biome, ecotope — which are sometimes organized serially from more comprehensive to less comprehensive. None of these subdivisions of a biosphere, however, would accurately describe the inhabited portion of a world on which biology does not culminate in a biosphere. Perhaps we will require recourse to the language and concepts of topology, since a biosphere, as a sphere, is simply connected. The bioring of a tidally locked M dwarf planet would not be simply connected in this topological sense.

If we conceptualize habitable zones not in terms of a celestial body being the right temperature to have liquid water on its surface, or perhaps in a subsurface ocean, but rather view this availability of liquid water as a consequence of habitable zones defined in terms of the presence of energy flows consistent with life as we know it, then we will need to investigate alternative sources of energy flow, i.e., distinct from the patterns of energy flow that we understand from our homeworld. Energy flows consistent with life as we know it are consistent with conditions that allow for the presence of liquid water on a celestial body, but this also means energy flows that would not overwhelm biochemistry and energy flows that are not insufficient for biochemistry and the origins and maintenance of metabolism.

Energy flows might be derived from stellar output (thus a consequence of gravitational confinement fusion), from radioactivity, which could take the form of radioactive decay or even a naturally-occurring nuclear reactor, as as Oklo in Gabon (thus a consequence of fission), from gravitational tidal forces, or from the kinetic energy of impacts. All of these sources of energy flows have been considered in another connection: suggested ways to resolve the faint young sun paradox (the problem that the sun was significantly dimmer earlier in its life cycle, while there still seems to have been liquid water on Earth) are the contributions of other energy sources to maintaining a temperature on Earth similar to that of today, including greater tidal heating from a closer moon, more heating from radioactive decay, and naturally occurring nuclear fission.

It would be possible in a series of thought experiments to consider counterfactual worlds in which each of these sources of energy flow are the primary source of energy for a biosphere (or a subspherical biological region of a planetary surface). The Jovian moon Io, for example, is the most volcanically active body in our solar system; while Io seems to barren, one could imagine an Io of more clement conditions for biology in which the tidal heating of a moon with an atmosphere was the basis of the energy flow for an ecosystem. A world with more fissionables in its crust than Earth (the kind of worlds likely to be found during the late Stelliferous Era under conditions of high metallicity) might be heated by radioactive decay or natural fission reactors (or some combination of the two) sufficient to generate energy flows for a biosphere, even at a great distance from its parent star. It seems unlikely that kinetic impacts from collisions could provide a sufficiently consistent flow of energy without a biosphere suffering mass extinctions from the same impacts, but this could merely be a failure of imagination. Perhaps a steady rain of smaller impacts without major impacts could contribute to energy flows without passing over the threshold of triggering an extinction event.

Each of these exotic counterfactual biospheres suggests the possibility of a living world very different from our own. The source of an energy flow might be inconsistent, that is to say, consistent up to the point of making life possible, but not sufficiently consistent for civilization, or the development of civilization. That is to say, it is possible that a planetary biosphere or subspheric biological region might possess sufficient energy flows for the emergence of life, but insufficient energy flows (or excessive energy flows) for the emergence of complex life or civilization. Once can easily imagine this being the case with extremophile life. And it is possible that a bioregion might possess sufficient energy flows for the emergence of a rudimentary civilization, but insufficient for the development of industrial-technological civilization that can make the transition to spacefaring civilization and thus ensure its longevity.

Civlizations of planetary endemism on these exotic worlds would be radically different from our own civilization due to differences in the structure and distribution of energy flow. Civilizations of planetary endemism are continuous with the biosphere upon which they supervene, so that a distinct biosphere supervening upon a distinct energy flow would produce a distinct civilization. Ultimately and ideally, these distinct forms of energy flow could be given an exhaustive taxonomy, which would, at the same time, be a taxonomy of civilizations supervening upon these energy flows.

However, the supervenience of civilization upon biosheres and biospheres upon energy flows is not exhaustive. Civilizations consciously harness energy flows to the benefit of the intelligent agent engaged in the civilizing process. The first stage of terrestrial civilization, that of agricuturalism and pastoralism, was a natural extension of energy flows already present in the bioshere, but once the breakthrough to industrialization occurred, energy sources became more distant from terrestrial energy flows. Fossil fuels are, in a sense, stored solar energy, and derive from the past biology of our planet, but this is the use of biological resources at one or more remove. As technologies became more sophisticated, in became possible to harness energy sources of a more elemental nature that were not contingent upon extant energy flows on a planet.

It may be, then, that biocentric civilizations are rightly said to supervene upon biospheres. However, with the breakthrough to industrialization, and the beginning of the transition to a technocentric civilization, this supervenience begins to fail and a discontinuity is interpolated between a civilization and its homeworld. According to this account, the transition from biocentric to technocentric civilization is the end point of civilizations of planetary endemism, and the emergence of a spacefaring civilization as the consequence of technologies enabled by technocentric civilization is a mere contingent epiphenomenon of a deeper civilizational process. This in itself provides a deeper and more fundamental perspective on civilization.

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Planetary Endemism

● Civilizations of Planetary Endemism: Introduction (forthcoming)

Civilizations of Planetary Endemism: Part I

Civilizations of Planetary Endemism: Part II

Civilizations of Planetary Endemism: Part III

● Civilizations of Planetary Endemism: Part IV

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