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When Microbes Ate the Ocean
museumpeace writes "When /. discussed a story about microbes that could break down water as a hydrogen source, many commentors went off on a tangent joking about runaway germs eating the oceans. Now, prof Joe Kirschvink and students at CalTech propose that indeed, the worst iceage ever, which nearly ended life on earth 2.3 billion years ago, was the result of algae evolving the ability to break down water and flooding the atmosphere with oxygen. The absence of oxygen consuming organisms at that time is said to have lead to destruction of atmospheric methane which had hitherto warmed the earth. The professor concludes: 'We haven't had a Snowball in the past 630 million years, and because the sun is warmer now it may be harder to get into the right condition. But if it ever happens, all life on Earth would likely be destroyed.'"
It didn't end all life on Earth, and it probably wouldn't if it happened again.
But if it ever happens, all life on Earth would likely be destroyed.
There's one unwavering faith I have in the human race: The ability to destroy things. That evil algae doesn't stand a chance!
I don't have a subscription to PNAS, so I could only read the abstract, but for what it's worth I think it goes like this:
All the evidence seems to be geochemical, e.g. they look at the chemical composition of rocks of a certain age and, knowing the chemical reactions that produce that composition, infer the chemical composition and temperature of the atmosphere at the time. This is not unlike the way the Mars Rovers are using the chemical composition of rocks on Mars to acquire evidence for or against the prior existence of liquid water.
They take for granted that everyone agrees there was a massive glaciation (the "snowball") at a certain time long in the past, and that the early atmosphere was reducing (high in methane, ammonia and water, low in oxygen and CO2), but underwent at another certain time, long in the past, and because of the evolution of photosynthetic organisms (the cyanobacteria), a fairly rapid change to an oxidizing system (high in free oxygen and CO2, low in methane and ammonia).
What they suggest is that the two events are not unconnected. By discarding certain evidence and adducing other, they argue the two events may be close in time. Hence there might be some connection.
The connection they suggest revolves around the facts that methane is a known powerful greenhouse gas, and the Sun was cooler in those days than it is now. I speculate they suggest the early Earth was unglaciated because large amounts of methane gave a strong greenhouse effect that compensated for the lower solar illumination.
But then the evil cyanobacteria (cue Imperial March music) evolved and started producing free oxygen like crazy, which reacted with the methane to produce water and CO2. Away goes the methane, away goes the greenhouse effect (since CO2 is less effective as a greenhouse gas than methane), and the Earth plunges into the deepfreeze.
Later, the Sun heats up a bit, so less greenhouse effect will keep the temps up, and also aerobic organisms start exhaling CO2 and farting a bit of methane, and all is once again serene.
The "close call" is because if the Earth were further from the Sun, like near the orbit of Mars, then there wouldn't be any replacement CO2 greenhouse effect, because the CO2 would just freeze out as dry ice.