a shadow biosphere & The Arrival [12/03/2007]

This cover story "Are Aliens Among Us?" in December's Sciam was actually my third choice after I read the bigfoot and semantic web articles, but this turned out to be the most interesting and intriguing science article I've read in quite awhile.

All life on earth that we know of is similar enough that we assume a single common point of origin. The idea explored in this article is there may be other forms of life here on earth (as yet undetected) that are so fundamentally different they do not share our same ancestral tree. If such life forms are found it would imply that life itself arose more than once, that there is more than one origin.

This alternate tree of life is referred to as a "shadow biosphere". These theoretical life forms are considered alien not because of their location of origin, which could be either on earth or extraterrestrial, but because of their biological differences.

Possible differences include:

1. silicon instead of carbon


2. mirrored handedness


3. different amino acids (not the our standard 20)


4. no ribosomes


5. arsenic instead of phosphorus


6. ethane or methane instead of water

It's interesting to me to think that life from earth with any of these differences may be more alien than life that shares our same biological characteristics and is not from earth. The idea of aliens existing undetected on earth reminds me of the movie The Arrival, which first got me thinking about looking for alien life on earth instead of in space.