Sunday, April 27, 2008

Photosynthesis Universalis

A couple of months ago, Scientific American posted an outstanding article titled The Color of Plants on Other Worlds. The part that impresses centers on the section titled Harvesting Light ... The way plants harvest sunlight is a marvel of nature. Photosynthetic pigments such as chlorophyll are not isolated molecules. They operate in a network like an array of antennas, each tuned to pick out photons of particular wavelengths. Chlorophyll preferentially absorbs red and blue light, and carotenoid pigments (which produce the vibrant reds and yellows of fall foliage) pick up a slightly different shade of blue. All this energy gets funneled to a special chlorophyll molecule at a chemical reaction center, which splits water and releases oxygen.

The funneling process is the key to which colors the pigments select. The complex of molecules at the reaction center can perform chemical reactions only if it receives a red photon or the equivalent amount of energy in some other form. To take advantage of blue photons, the antenna pigments work in concert to convert the high energy (from blue photons) to a lower energy (redder), like a series of step-down transformers that reduces the 100,000 volts of electric power lines to the 120 or 240 volts of a wall outlet. The process begins when a blue photon hits a blue-absorbing pigment and energizes one of the electrons in the molecule. When that electron drops back down to its original state, it releases this energy—but because of energy losses to heat and vibrations, it releases less energy than it absorbed.

The pigment molecule releases its energy not in the form of another photon but in the form of an electrical interaction with another pigment molecule that is able to absorb energy at that lower level. This pigment, in turn, releases an even lower amount of energy, and so the process continues until the original blue photon energy has been downgraded to red. The array of pigments can also convert cyan, green or yellow to red. The reaction center, as the receiving end of the cascade, adapts to absorb the lowest-energy available photons. On our planet’s surface, red photons are both the most abundant and the lowest energy within the visible spectrum.

Because photosynthesis is a quantum mechanical process able to function under different star types (Click on the above graphic to see Sciam's take on this.), the chances of finding life on other worlds should not be a big deal save for the fact man will finally know that he is not alone.

When this process is combined with chemosynthesis, the possibility of life existing on other worlds really takes off as the need for sunlight disappears and, as Jeff Goldblum says in Jurassic Park, Life Finds a way.

For other BRT blurbs on this subject, The Goldilocks Zone and Life Finds a Way indicates that thinking earth is the only place where life resides is somewhat far fetched to say the least.

Regarding intelligent life, I agree with Stephen Hawking in that it's rare but not beyond the realm of possibility because if it is, then nature has paid a cruel joke on this universe by having us as it's sole representative of intelligent life.
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