The atmosphere doesn't just keep you alive and protect you from the sun - it is responsible for the face of life as we know it. One-fifth of the atmosphere is oxygen, happily waiting to accept electrons from whatever's available. Oxidative metabolism turns sugars and the like into CO2, just like fire. This provides loads of energy, of course. This wasn't always the case!
Long ago, there was virtually no O2. During the course of evolution, some humble microbes began to produce oxygen. This wasn't by design, mind you - the oxygen was waste! Photosynthetic bacteria, like plants, gave off oxygen when they used the sun's energy to split water (providing useful energy).
That's the dirty secret of metabolism: oxygen was once useless, toxic, bacteria poop. Life's evolution of the ability to harness said spoor caused a profound change in the world.
Slowly, the world changed. Bright, shiny metals became the boring ores you know today. This was no small feat - oxidizing everything that's easily oxidized took a lot of oxygen. It's estimated that the world's oxidized iron alone contains as much oxygen as six of our atmospheres!
This rock is ~30-40% oxygen, by weight.
Image source: Andre Karwath. Governed by these License Terms.
All this oxygen was produced by photosynthetic bacteria. 800 pounds of a one ton rock - primordial bacteria poop!
So life changed. The benefits of all this O2 were enormous. The comparatively vast amounts of energy provided by oxidative metabolism engendered an, ahem, sea change. Rather than lazy microbes floating around in the ooze (oh, thanks for the O2, guys), we were about to see flagella, flippers, and legs - time to party down, life!
The hangover accompanying the party was called the oxygen catastrophe. Oxygen's toxic. Life that preferred the anaerobic lifestyle died or was forced into the muck (anaerobes would later enjoy some revenge hiding out in bulging tin cans.). Some stuff tolerates oxygen but doesn't particularly like it, some stuff just withers in its presence.
Nothing is immune to oxygen's effects, though - oxygen inevitably occurs in some forms that are toxic to all life - even us aerobes. Some of these are those free radicals supplement manufacturers keep bleating about. Whether you take a gram o' C a day or not, though, your body has some mechanisms for handling oxidative stress.
Despite the fact that we live in a profoundly oxidizing atmosphere, your cells are a profoundly reducing environment. Those golden oxidizing equivalents are shuttled around in the cell by the agency of certain small molecules that fit into enzymes and do the dirty work - the scalpel to molecular oxygen's grenade.
Whatever reactive oxygen species are present are neutralized by things like glutathione, above, which gets oxidized to a disulfide-linked dimer:
Glutathione, being so useful, has evolved numerous roles in metabolism beyond that of a simple antioxidant. Tomorrow, I'll explain why Tylenol would kill you if you didn't have the stuff!
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My uncle was not a monkey! I mean poop-eater!
I think your theory that we evolved to eat poop is clearly false. If it were true, and even smarter species than us would be eating our poop!!!
If we evolved from apes, then why are the apes still here?
(ACTUAL comment from a Witless at my door - bastard even looked like a monkey- very small cranial cavity)
not only does glutathione help protect against certain oxidizers it also helps plants accumulate cadmium. http://www.plantphysiol.org/cgi/content/abstract/119/1/73
MarkH: if they're smarter than us, they'd probably be hiding, lest we'd preemptively kill them off. has anybody done a thorough check of the sewers lately?
MarkH: if they're smarter than us, they'd probably be hiding, lest we'd preemptively kill them off. has anybody done a thorough check of the sewers lately?
One thing I've wondered -- given that the elements below it in the periodic table get progressively nastier in smell as you go down (with the possible exception of polonium, whose compounds no one wants to get anywhere near enough near them to smell), is it a good thing that we (and presumably most of the rest of the animal kingdom) have evolved without the ability to smell O2?
Why put in all of the speculation about the oxygen catastrophe and "Long ago, there was virtually no O2.". We have no clue how life started - and to say that anaerobic bacteria were the first and aerobic bacteria evolved from them is complete wishful thinking. Read that latest Scientific American to see how difficult it is to create life - and you make it sound so deceptively easy. You are being misleading by pitching idle speculation as concrete truth.
Nice BIF!
Bill, the first evidence of significant O2 in the oceans comes a billion years after the first evidence for life. Thus the first life must have been anarobic, even if the exact mechanism of evolution is not yet known. It is another 2 billion years (more or less) before fins, flippers, etc start to appear.
It is worth pointing out, however, that the oxidation merely changed dissolved Fe 2+ to insoluble Fe 3+ (Fe2O3 or hydroxide). There was no metallic Fe on the early earth, as it would have been oxidized by water to form carbonate or magnetite + hydrogen gas.
The use of glutathione gives a lot of benefit to an individual.Aside from it is a very powerful anti-oxidant it also helps whiten skin. For more information on Glutathione a visit to this site may be helpful: Glutathione Benefits