Life

The Terragenid group is classified as organic multicellular lifeforms, of both marine and terrestrial biomic types. However, a significant percentage of terragenids are unicellular, and the planet has a poorly-studied aerial biome.

— Example biospheric classification

Life is a fundamental concept in a universe which happens to be relatively teeming with it. The nature and definition of life have been debated over and speculated upon by the philosophers and scholars of all sophont species throughout spacetime. At the formation of the United Spacefaring Sophonts Coalition, a solid universal definition of life and biospheric classification system was agreed upon to discourage the potential for discrimination later on and help biologists better understand their field of study. Under this definition, life is characterized by the following attributes:

• The ability of the entity in question to consistently regulate its own internal entropy.
• The ability of the entity in question to replicate all or parts of itself, independently, regardless of the type of biophysical unit replicable; or the ability to reproduce sexually; or the ability to replicate its consciousness.

• Inertia-independent reaction to stimulus, however slight and regardless of speed.
• The independent production or collection and internal storage of energy for self-use, including but not limited to: active biological molecular processes^[1], capacitor structures, nanoscale electrothermal turbines, etc.

Contents

Biosphere Class System

1. Biogenesis
2. Basis
   • Organic
   • Exotic
3. Structure
   • Protocellular
   • Unicellular
   • Multicellular
4. Biomics
   • Terrestrial
   • Marine
   • Subglacial
   • Aerial

Abundance

• Biochemistry
• Complexity
• Extinction

Footnotes

Biosphere Classification System

A planet's biosphere, if it has one, has a fairly simple classification system of its own, determined by a few key factors.

Biogenesis

Beyond the general biotic class system, a new tier of taxonomy was added to the extant phylogenetic system to denote the different abiogenetic origins of organisms. Genesis groups are a rank above domain intended to separate the myriad trees of life across known space by indicating where their abiogenesis^[2] took place. The skae of the planet Ra'na in the Tau Ceti system, for example, have a taxonomy that looks something like the box to the left. In the cases of panspermia^[3], panspermic notations are used to indicate the phylogenetic point at which the interplanetary migration occurred.

Example Phylogeny

Ranagenids (genesis group)

• Taukarya (domain)
  • Tauzoa (kingdom)
    • Alysidata (phylum)
      • Placospondyla (subphylum)
        • Hexapodomorpha (superclass)
          • Terrambulatis (class)
            • Arthrodactyla (order)
              • Centauridae (family)
                • Xenocentaurus (genus)
                  • sapiens (species)

Basis

Organic

In the broadest sense, organic life is based on the interactions of carbon and carbon compounds. It is the most common type of life in known space, due to carbon's commonality, but the element's versatility results in a vast array of carbon-based biospheres that are nigh irreconcilable with each other.
The Proteagenids, for example, have evolved on a nephelic world whose ultra-dense, ammonia-rich atmosphere have produced a biochemical system radically different from, for instance, terragenids. This biochemical diversity is potentially catastrophic for first contact events, though stringent measures have been taken to prevent such a disaster.

Exotic

The term exotic in the context of biospheres refers to any form of life not based solely on carbon-dominant chemistry. While not nearly as common as purely carbon-based life, a small percentage of the known genesis groups are based at least in part on the elements nitrogen, silicon, and aluminum.
Even within these known bases, there is a considerable extent of structural variation due to environmental diversity, as expected from a sample size of 270 star systems. Still more types of exotic life exist purely as hypothetical concepts, such as organisms based on lead, heteropolymic acids, plasma helices, and even radio pulses.

Form

Protocellular

by National Science Foundation

Protocellular lifeforms are a rare but incredibly varied class of organisms that meet only some of the criteria for life. This may come in the form of self-replicating polymers, free RNA or RNA analogues, or lipid clusters which perform metabolism but cannot replicate. These first recognizable signs of life are typically found on young, solvent-rich worlds with active suns. Protocellular organisms form extremely simple relationships with each other and their environments.

Unicellular

by Ye Maltsev

Unicellular lifeforms are by far the most common form of life in known space; roughly half of all documented biospheres are entirely comprised of single-celled organisms. This is not to say that planets with more complex life are devoid of unicellular life; quite the opposite in fact. As the hardiest biostructural class, single-celled life can be found on almost every known type of planet. Unicellular organisms form fairly simple relationships with each other and their environments.

Multicellular

by Bonnie Taylor Barry

Multicellular lifeforms are the second most common form of life in known space, trailing behind unicellular life by half. It is the broadest category of organism structure, with organisms ranging from sophonts to Thalassian orbmoss fitting under the multicellular umbrella. Complex life is found on older planets whose geology and solar activity have mellowed. Multicellular organisms form complex relationships with each other and their environments, giving rise to visible macroecology.

Biomics

Terrestrial

Canyon Shadow by Midiaou Diallo

Terrestrial biospheres are a fairly common biomic type comprised of life that primarily dwells on (or, more rarely, within) the solid surface of their homeworlds. This type of biosphere is found most frequently on terrae and aquarae, though some chionic and desert worlds have terrestrial life as well. Terrestrial biospheres are typically macroecological as well as microecological, and are one of the more diverse biomic types in terms of biochemistry and evolution.

Marine

Barnard's Swordswallower by Alex Ries

Marine biospheres exist solely within liquid solvent on a planet's surface. Marine life is the most common biomic type, of course, being found quite commonly on oceaniae, terrae, and aquarae. However, the line between marine and aerial biomic types is blurred in the cases of supercritical atmospheres such as those on oceaniae and nephelae, which are something between ocean and sky. Marine life typically resides in water oceans, though hydrocarbon- and ammonia-housed marine biospheres are known to exist.

Subglacial

Icy Moons Probe by Alex Ries

Subglacial biospheres are characterized by their existence underneath or within the solid icy crust of their homeworlds. This biomic type occurs almost exclusively on erimae and chionae, though a few aquarae have subglacial life as well. This biomic class is most often similar to marine life, as life on cryonic planets typically subsist within oceans. However, subglacial life is distinct in its lack of contact with the sea's surface, as the interior ocean directly borders the ice above it.

Aerial

Edge of the Troposphere by Midiaou Diallo

Aerial biospheres are the strangest biomic type in all of known space, as they are composed entirely of organisms that spend their whole lives airborne; either volant, aerobuoyant, or both. This type of biosphere is only found on joviae and nephelae, with the sole exception of the vulcanic planet Nuyo in the Gliese 754 system. Because of this, known aerial biospheres are almost always exotic in chemical composition, needing to rely on unusual metabolism to survive in the volatile atmospheres of giant gaseous worlds.

Abundance

Just over 20% of all documented star systems within known space have some form of native biosphere, which is a much greater percentage than scientists of previous ages had anticipated. Many of these systems have multiple life-bearing worlds due to natural panspermia events, bringing the total number of naturally-occurring planetary biospheres to 62.

Biochemistry

Every known biosphere utilizes organic chemistry at least in part, lending heavy support to the theory that carbon is the ideal basis for living systems. The vast majority of biospheres on temperate planets are purely organic, with five cases of organonitrile life; all of these use water as their primary solvent. Biospheres that evolved in temperatures lower than the freezing point of water tend to use organonitrile chemistry and ammonia instead, though the protocellular life on Ninlil and the microbes of Murray-Callahan reside in lakes of liquid hydrocarbons. Only one high-temperature biosphere has been documented so far: the aerial microbes of Nuyo, which are based on organosilicon chemistry and use sulfuric acid as a solvent. Twelve natural biospheres depend primarily on hydrogen/methane metabolism, two use the sulfur cycle, one (the Ashgenid group) uses the iron cycle, and the rest are dependent on oxygen/carbon-dioxide metabolism.

Complexity

Approximately half of all documented cases of abiogenesis have resulted in multicellular life, though studies suggest this may just be dependent on the age of the biosphere –the longer life exists on a world, the more probable the development of multicellularity becomes. Multicellular life is most common on terrestrial worlds, and quite rare on gaseous worlds.

Extinction

While mass extinction events are relatively ubiquitous across life-bearing worlds, there are only two known cases of naturally-occurring biospheres which have gone completely extinct: Indrani and Ashtara. Both of these worlds are moons of gas giants, and geologic evidence indicates they experienced drastic changes in their orbital patterns early enough in their biotic histories to render them uninhabitable to all life. Once life is firmly established on a planet, it is extremely difficult to extirpate all of it. However, it is possible that many biospheres on oceanic or gaseous planets have fully gone extinct, as there is no way to recognize the prior existence of an extinct biosphere without fossils -a phenomenon unique to terrestrial worlds.

Footnotes

^[1] Active biological molecular processes are defined as: the intake, internal reaction, and output of chemicals between the environment and the entity in question.
^[2] Abiogenesis is the natural spontaneous development of biology from an abiotic environment.
^[3] Panspermia is the interplanetary spread of one kind of life from its abiogenetic homeworld to other places in the cosmos, naturally by impact ejecta but more frequently by artificial means.

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