Arsenic-based Life
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Basic Information

Phosphorous is used in every cell in standard terrestrial life, as it is a major component in both DNA (the basic building block of life) and ATP (the main cellular energy source). Arsenic is adjacent to Phosphorous, and in the same column, on the Periodic Chart. As such, it has many similar properties. "As" can stand in for "P" in many chemical reactions, but Arsenic tends to form less-stable compounds than Phosphorous. What's more, arsenic is toxic to most terrestrial life. To humans, it is very poisonous.

It is theoretically possible that life could evolve, on Earth, or elsewhere in the Universe, that could process Arsenic much as standard earth life does Phosphorous. Such "Arsenolife" might even build DNA, or it's equivalent, from Arsenic-derived alternative Amino Acids.

Recently, NASA announced that they have discovered GFAJ-1, a new form of naturally-occurring extremophile bacteria that appears to use Arsenic in it's own variants of DNA and ATP. GFAJ-1 can be cultured and survive on either Phosphorous or Arsenic. When dining on Arsenic, it grows 50% larger. The extra size is taken up by vacuoles that may contain Polyhydroxybutyrate or a similar chemical to isolate and stabilize various arsenic compounds.

There's still some debate and speculation going on about what qualities exactly GFAJ-1 or other arsenic life would have. Some of the microbes at the lake where GFAJ-1 was found can use Arsenic instead of Water in the photosynthesis process. There are also organisms that can "breathe" arsenic instead of (or in addition to) Oxygen. Remember, though, that stabilizing Arsenic compounds isn't easy. On paper at least, DNA-equivalents made of arsenic should break apart when exposed to common water.

These discoveries indicate that life in the cosmos is not actually restricted merely to the places we'd previously assumed it was. Science had largely assumed life needed Phosphorous and Water to continue. The new NASA findings suggest life could well thrive without them.

GFAJ-1 and other "Arsenolife" would likely use Carbon just as standard Carbon-based life on earth does. So the term Arsenic-Based Life may be a little misleading in regards to such organisms, as they would still use large amounts of Carbon and other compounds.

True "Arsenic-based life" could remain an outside possibility, though, perhaps using methods akin to hypothetical descriptions of Nitrogen- and Phosphorous-based life, perhaps on a planet with little carbon or water.

Sources

Game and Story Use

  • Arsenolife could constitute a Shadow Biosphere of many types of Shadow Life hidden in places we'd previously thought uninhabitable here on earth.
  • A planet lacking Water, Oxygen, Phosphorous, or Carbon might feature Arsenic-based life of one sort or another. Such creatures would be very alien, and interacting with them would be difficult.
  • There's a movie I can't name because I don't want to spoil it… but suffice it to say this movie has a very strange revelation near the end that water is like acid to the menacing aliens in the film. When first watching it, I thought that sounded kinda silly. Now, however, I'm forced to conclude that it's possible, if the alien's cells had Arsenic DNA. One could steal various ideas from that film, and the players just might get the references.
  • In the case of GFAJ-1, the cells are 50% larger when cultured in Arsenic. One could extrapolate from that, and assume that arsenic-based life-forms are going to be generally quite large.
    • If some Mad Scientist figured out how to convert ordinary DNA into arsenoDNA, the monsters he'd create could be giant, toxic, water-soluble versions of normal animals.
      • The PCs are being hunted by the scientists over-sized tiger. Its huge claw attacks are poisonous, earning it two stacked damage bonuses. However, ordinary tap water is a weapon against the beast. If the PCs can get to the shore and wade out a few feet, the tiger won't chase them any further. Heck, just spitting on the tiger will do 1d4 non-lethal damage.
  • Water breaks down Arsenic DNA. Some existing real-world microbes use arsenic instead of water in a photosynthesis-like process. Therefore, it seems only natural that a planet (or other adventure setting) could have some sort of arsenic-based plant life. See also Non-Green Photosynthesizers.
  • For further ideas, see Alien Biology, Alien Amino Acids, Non-Water Biological Solvents, and Hypothetical Types of BioChemistry.
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