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."

Re:Plants on other planets

[TheThiefMaster]

Anyway, I'm kind of a skeptic already, I don't think that looking for life outside our galaxy is particularly interesting or useful anyway, considering that the nearest life would be millions of years away by interstellar travel. Even if it's out there, we'll never meet it or communicate with it.

Who said we were looking for life outside our galaxy?

We are still on the "looking for life outside our solar system (but inside our galaxy)" stage. We're not even certain that there isn't other life in our solar system, even if it is only bacteria or moulds.

Photosynthesis is non-optimal

[Flying pig]

Actually, photosynthesis is a complex process involving not one but two photons and some clever quantum effects. You have it exactly the wrong way round. Plants are (usually) green because they have evolved a process which uses two frequency bands of light. Such a mechanism would not have evolved unless either:

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.

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.

Re:Plants on other planets

[49152]

That "almost-Earth-like" planet is inside our own galaxy, just about 20 light years away. This makes it one of our closest neighbors even compared to the distances within our own galaxy.

Finding planets in other galaxies is way beyond our current capabilities.

I do not know much about SETI but always believed they just piggy back on other projects and look for sign of intelligent life (radio signatures) in whatever the other projects might be looking at - in our own galaxy or not. Perhaps someone would care to elaborate.

Re:Plants on other planets

[Falladir]

He's got more imagination than sense. Don't worry about him. He's thinking of crystalline creatures from Star Trek and generic "energy-beigns", and if you dismiss these things, he'll just say you're closed-minded.

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 [newport.com]
- Absorption-spectrum [uic.edu]

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.

Scientists already know why plants are green

[JayBees]

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:

http://blog.myspace.com/index.cfm?fuseaction=blog. view&FriendID=187945&blogMonth=9&blogDay=24&blogYe ar=2006 [myspace.com]

Re:Plants on other planets

[pongo000]

And here, all this time, we thought it was all about Rayleigh scattering [gsu.edu].

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

Re:Plants on other planets

[BlackSnake112]

Stalactite : are the ones that 'grow' from the ceiling. They have to hold on tight.

Stalagmite : are the ones that rise from the ground. They are mighty and rise up.

That is about the only thing I remember from 8th grade science class. The teacher was 23 super hot, wore very revealing outfits, and (when I turned 18...) a great kisser. She rocked, well still does..

Re:Plants on other planets

[Anonymous Coward]

I remember episodes of ST: TNG where life were very different, ranging from energy beeings to crystal life forms

Re:Still fighting old battles

[GospelHead821]

We haven't observed much life, but we do know quite a bit about chemistry. There is good reason to believe that the complexity of life requires delicate chemistry which can be conducted easily in water. This is one of the prime arguments I've heard against silicon-based life, for example. The molecules are too fragile to form chemical constructs analogous to those found in carbon-based life. Likewise, life that does not use water as a solvent would have to overcome some very basic chemical obstacles to developing molecules of sufficient complexity to qualify as life-forms.