Now this is really cool. Almost all life on Earth is made up of amino acids that are “left-handed” (by which I mean, the molecules are oriented in one particular manner as opposed to the other, even though a molecule could exist in one of two orientations and still be the same molecule — like how your left hand and your right hand are not identical, but are both still hands). This handedness, or “chirality“, has an interesting effect when it comes to chlorophyll in photosynthesizing plants, which absorb the ultraviolet portion of the spectrum and reflect the green, the most “active”, portion of the spectrum. You see, light can have chirality as well, and when light bounces off of an object, it takes on the chirality of whatever molecule it bounces off of. Because almost all the life on Earth is left-handed, light bouncing off of Earth (and thus the copious amounts of plant life) would come back mostly left-handed. Except archaea, which is the group of bacteria-like, but unrelated to bacteria, life forms that can withstand some wicked extremes of temperature and acidity, but this is mostly found near volcanic vents, acid runoff from mines, etc.
The upshot of knowing that most of the life on this planet picked a chirality, is that it might be a property of life itself that once the runaway chain reaction begins, it might naturally swing toward one chirality or the other, and as a consequence, we might be able to remotely discover whether a planet discovered elsewhere in the universe has life on it, based on the uniformity of the light’s chirality. The only potential stumbling blocks to this technique are the light bouncing off intermediary material such as our atmosphere, nebulae, etc., and the sensitivity of our equipment. We’d need a very big, very powerful telescope outside the confines of our planet to get a good enough glimpse of an extrasolar planet, and the knowledge of that planet’s star enough to be able to weed out what light is bouncing off the star and what’s coming straight off the planet. We’d need a really good look at that planet, in other words, before this could even be tested. For the time being, testing whether or not the light bouncing off of, say, the moon, or Saturn, has the same chirality, should prove interesting to suggest whether or not this is even a viable indicator of the presence of light.
Incidentally, the makeup of molecules’ chirality as defined as being left-handed on Earth, might be wholly arbitrary — just because we see molecules occurring in nature in both hands, doesn’t mean that the righthand orientation is particularly right-handed. To illustrate, if you see a molecule structured as ABC and CBA in nature equally, and all life happens to have that molecule in CBA format, doesn’t mean CBA is by necessity left-handed — we just arbitrarily picked one as being the “right” makeup of the molecule, and its mirror image being the “left” one. Rotate them 180 degrees and suddenly the left is on the right and the right on the left, but the molecules are still mirrored to one another.
A few people at work recently told me I missed my calling (independently of one another, even). I dunno. I’m such a layman at this stuff that I probably got half of this entry wrong, and don’t even realize it.