Known Types of Xenobiochemistry
There are many forms of "life", both natural and artificial, within
the
Terragen sphere. These include various self-replicating machines, with
or
without nanotech components, sometimes entirely artificial or
sometimes, in the
case of the botworlds,
naturally evolved from abandoned or
escaped originals. There are also many forms of life that appear to
have a
natural origin but do not employ biochemistry as the term is normally
used (the Rheolithoids
and the Hildemar's
Knots are good
examples of these). There are even a number of neogens
with novel
artificial biochemistries, such as the famous fluorine breathers of the
Chen
Zhuo 1101 habs. However, the known naturally evolved biochemistries
discovered
so far can be divided into just a few broad categories: methane based,
ammonia
based, and water based. This might be predicted on the basis that these
are all
combinations of hydrogen, the most common element in the universe, with
the next
three most common elements that are capable of forming compounds with
it. There
are many subtypes of these basic biochemistries, of course, and there
is huge
biochemical variety between and within biospheres, but there are also
broad
similarities. In all cases there is considerable variation around the
mean
temperature at which these life forms can operate. The broadest range
is the
Terragen type, since water is liquid over a larger range than are the
other
common solvents. The other two major types of life are active over a
much
smaller temperature range, but they can typically survive much greater
dips in
temperature in inactive, frozen form. This is because the solutions
they depend
on do not expand when they solidify the way that frozen water does.
Some experts include a fourth classification called Jovian, or
Jovic. However, such life forms typically use one of the above
styles of
biochemistry, according to the temperature and pressure regime of the
local
atmosphere. In a few celebrated cases the planet's biosphere includes
all three
of the other types in variant forms. However, these are believed to be
the
result of seeding by sophonts, Terragen or otherwise.
Type I (Terragen/Water-based)
Type I life typically operates at about 20° to 30° C, with variant
forms that
thrive at temperatures as low as 0° C or as high as 125° C; all life
forms of this
type use H2O as a solvent. A well developed planetary
ecosystem
eventually evolves forms capable of photosynthesis with water as the
hydrogen
donor and produces an oxygen/nitrogen/carbon dioxide atmosphere, with
anything
from trace amounts of carbon dioxide (for planets like Old Earth that
are near
the inner edge of the Type I life zone) to much larger amounts (for
planets that
are further out from their primary and maintain type I life by a strong
greenhouse effect). Typical chemicals are proteins, fats,
carbohydrates, and
nucleic acids. This is by far the most common type, since oxygen is the
third
most common element in the universe and water is liquid over such a
broad range
of temperatures and pressures. It is generally associated with the
Gaian
planetary type, but any environment that allows liquid water may give
rise to
type I life forms. Examples are numerous: Old Earth,
Trees, Kemmerer, Ridgewell, Darwin
, Euripedes
Mey, Whisper,
Orwell, Eden, the
biological component of Cybyotan
worlds, the Auld
Limner worlds, and the homeworlds of the Daharrans,
the Cthonids,
the Paulans,
the Meistersingers,
the Singers,
the Silent
Ones, and the Gnosags,
to name only a
few.
Type Ia (To'u'ulhian/Hot Water-based)
Type Ia is like type I in most respects, but operates at 125° to150°
C.
The
extremely high surface pressures (up to 100 or more bars) allow the use
of water
as a solvent since at such pressures it remains a liquid. There is a
much larger
fraction of carbon dioxide in the atmosphere, usually 50 to 90 percent
of the
total, but oxygen is also present in a fully evolved biosphere of this
type.
This biochemistry features the addition of a number of minor elements
that are
volatile at these temperatures, such as mercury and tin. Sulphur is
also more
frequently employed in the local biochemistry than in standard Type I
biology.
Usually the ecology includes some high altitude cloud dwelling life
forms that
are more typically type I, and are extremophiles in the context of
To'u'ulh
worlds. Some experts regard types I and Ia as simply two extremes on a
continuum. This is a less common type, than regular type I
biochemistry, since
the strong insolation that leads to To'ul'hian life more often leads to
a
runaway greenhouse effect and desiccation of the planetary atmosphere
resulting
in a lifeless world of the true Cytherean
type.
The associated Planetary
Classification
type
is Cytherian/Gaian, (To'ul'hese
subtype). The To'ul'h homeworld is the archetype and the richest
natural
example.
Type Ib (Halogenic/Water-hydrochloric acid based)
Type Ib is like the above two, but the solvent mixture includes some
HCl in
addition to water and the atmosphere includes a fraction of chlorine
gas as well
as oxygen. The associated planetary type is Gaian ( Halogenic).
Examples include Chorus,
Doreen, Tytalus
, and Outland.
Such biospheres are vanishingly rare due to
the relative scarcity of chlorine. There is only one known origin to
this type
of life, and the entire group may ultimately prove to be artificial in
its
ultimate origin, despite hundreds of millions of years of subsequent
evolution.
Type II (Softoneian/Water-ammonia based)
Type II life operates at about -50° C. The solvent is an H2O
and NH
4 mix, and the biochemistry involves extensive use of fatty
acids.
The associated planetary classification type is a Europan
variant.
There are only a few natural occurrences, of which the Soft Ones
are the most famous.
Type III (Muuhian/Methane-ethane based)
Type III life operates at approximately -160° C. The primary solvent
is a
mixture of methane, CH4 , and ethane, C2H6.
Methane alone has an extremely narrow range over which it is a liquid.
As the
primary solvent is nonpolar, the biochemistry of such life forms has
few
analogues with typical Terragen life. The typical atmosphere is
composed of
nitrogen and methane with heavier hydrocarbon gases as contaminants. It
is very
rare. The associated planetary classification type is Titanian
( Titan
in Solsys
is a
chilly and barren version). Known
examples are Muuhome
and
other Muuh
worlds.
Related Pages
Xenobiology
Xenophotosynthesis
Chlorine Worlds
