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."

Comments

Re:Plants on other planets

[owlnation]

I can't understand people who think that to find life on other planets we have to look for conditions similar to Earth.

I guess the simple reason is that people's imaginations have been constrained by TV budgets. Earthlike is cheaper to produce and design, being the reason why the aliens in ST TOS all kind of looked a bit Middle Eastern, and in ST TNG they all had funny foreheads.

Still fighting old battles

[Flying pig]

I belive that one reason is that scientists are still trying to defeat, with evidence and reason, the religious fundamentalists who believe we are the only "intelligent" life in the Universe, and on the only planet that supports life. On this argument, which I personally doubt, conclusive evidence that life existed elsewhere in the universe and could make itself known would cause the collapse of fundamentalist religions, to the enormous benefit of the rest of us.

I don't buy into it because (a) these people aren't rational and (b) taking away their religion could make them worse - they could easily be converted into Stalinists or extreme nationalists. But I am sure that this, as well as the desire to get budget for exploration, is one of the factors in the search for life on Mars, and in SETI.

Finally, looking for water is not irrelevant. Any practical life form is going to need a solvent and carrier for the various chemicals it needs to get from place to place internally. Water is unique because its strong hydrogen bonding gives it a wide liquid temperature range. Other small molecules which are good solvents also tend to have very low boiling points, meaning that the range of reactions that can take place in them is much more limited. Water has very unusual properties, in fact, that make it more probable that life would evolve on a planet with lots of liquid water than, say, one covered in methane or liquid carbon dioxide.

Re:Plants on other planets

[Rob Kaper]

I can't understand people who think that to find life on other planets we have to look for conditions similar to Earth. All of the hubbub over liquid water seems so silly to me.

It would be silly to exclude conditions not similar to Earth alltogether, but it is definitely reasonable to focus on conditions that are similar. Other conditions could qualify but that's pure speculation, for the conditions we live in we actually have a proof of concept. I'll take the refined "it works here, so why not elsewhere" over "anything could work" any day.

Your idea of looking for non-natural patterns is interesting but note that it would very much limit search results to life so intelligent that like ourselves we would consider it above natural. You wouldn't find any microbes on Europe because in our frame of reference they too would be very natural.

Re:Plants on other planets

[ResidntGeek]

Looking for liquid water isn't just human arrogance. Water is an effective and stable polar solvent, and there aren't many chemical processes as widely applicable as hydrolysis. In addition, the presence of liquid water indicates temperatures cool enough to allow organic molecules to stay stable, but warm enough to undergo the reactions necessary for life. These things are true throughout the universe, not just here.

Re:Plants on other planets

[ResidntGeek]

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.

Wrong!

[bananaendian]

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

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.

Re:Plants on other planets

[pongo000]

And here, all this time, we thought it was all about Rayleigh scattering.

I guess the collective wisdom of /. moderators trumps all!