Slashdot Mirror
When the Earth Was Purple
Ollabelle writes "It's always been a bit of a mystery why plants absorb red and blue light, reflecting green, when the sun emits the peak energy of the visible spectrum in the green. A new theory offers one possible answer: that the first chlorophyll-utilizing microbes evolved to exploit the red-and-blue light that older green-absorbing microbes didn't use, eventually out-competing them through greater efficiency and the rise of oxygen."
The original form of photosynthesis resulted in a different metabolic pathway which used red or blue light and evolution took care of the rest
There were some conditions on the Earth at that time which meant that only red and blue light was available at the intensities required.
There are many possibilities why this might be so, including the nature of the media in which the first synthesising bacteria lived. I suspect the explanation when it is eventually found will be very interesting. However, it is by no means obvious that there is not a much simpler photosynthetic pathway using a single photon absorbtion, and it did not evolve simply because the conditions at the time - the predominant biochemistry of the bacteria and the wavelengths of light falling on them - were not suitable.
Pining for the fjords
The problem boils down to carbon. Of all the elements on the periodic table, there is one (1) which acts like carbon. Other molecules like nitrogen and silicon can form long chains and rings like carbon, but they don't like it. Carbon _loves_ forming itself into complicated molecules that cooperate to reproduce. There might be some non-carbon-based form of life out there, but it's very unlikely, and even if it does exist wouldn't easily evolve to macroscopic scales. It's just so unlikely there's no point looking for it.
Once you accept that life is carbon-based, the rest follows. All we know about organic chemistry, and the temperatures and conditions it requires for optimum function, apply everywhere. Heat that breaks down carbon chains and makes life unlivable in the lab makes life unlivable on a planet orbiting too close to its sun, too. Water, which is pretty much the ultimate solvent here, allowing acid-base chemistry to exist, hydrolysis and dehydration synthesis to take place, protein microdomains to move diffusively.... it all happens on other planets too. While we shouldn't look for pretty blue centaurs with eye stalks or humans with funny ears, carbon-based life is a pretty good bet fi we're looking for anything.
ResidntGeek
No, it doesn't!
- Solar irradiance at sealevel
- Absorption-spectrum
Solar irradiance at sealevel 'peaks' at 470nm which is exactly where chlorophyl-B absorption peaks. In fact the 'peaking', when put into context, is somewhat vague, since throughout the whole visible spectrum from 400nm - 700nm you have well over 50% of the real watts that you get at the peak 470nm, so an adaptation to a particular wavelenght within it gives at most only a conservative if not marginal advantage.
www.tribalnetworks.org - helping tribal people around the world to own their own means of high-tech communications
It's pretty obvious once you know the argument. It's due to light-scattering. There's so much energy in the sky all day that it doesn't matter what color you absorb, there's plenty at any visible wavelength. But during sunset and sunrise there's predominantly red light in the sky, and a green plant would be more efficient at absorbing red light (they're complementary colors) than if the plant were another color. This blog entry goes into it:
. view&FriendID=187945&blogMonth=9&blogDay=24&blogYe ar=2006
http://blog.myspace.com/index.cfm?fuseaction=blog
And here, all this time, we thought it was all about Rayleigh scattering.
/. moderators trumps all!
I guess the collective wisdom of