This reminds me of one of my favourite pieces of science writing ever: "Bands of Iron", by Adam Lee[0]. I don't think I've ever read something that better conve

This reminds me of one of my favourite pieces of science writing ever: "Bands of Iron", by Adam Lee[0]. I don't think I've ever read something that better conveyed a sense of Deep Time[1] in the context of life on this planet: > Unlike today, there were no oxygen-breathing animals to expire carbon dioxide and close the cycle, and so it quickly built up in the atmosphere as photosynthetic bacteria spread and thrived. To us, it’s the breath of life, but to these bacteria, it was a deadly toxin. Luckily for these bacteria, there was iron that could react with this oxygen, keeping the atmosphere liveable for a while. That is, until the iron ran out and oxygen build up in deadly concentrations: > The consequence was mass death among the planet’s abundant bacterial colonies – an oxygen holocaust that knocked life back down to nearly nothing. Only a few anaerobes survived, in isolated nooks and crannies where the deadly gas did not reach. > After this catastrophe, the planet would have seen several million years of relative quiet. In this life-poor era, layers of silica minerals were deposited on the ocean floor. But in the meanwhile, erosion continued to free up iron atoms, which slowly scrubbed the atmosphere and oceans of oxygen. > Eventually, the world was cleansed, and life bounced back, spreading from its refuges to once again cover the planet. Of course, this exuberance contained the seeds of its own downfall – bacteria still spewed out the waste oxygen that they could not abide – and the cycle repeated, not just once but many times. Each time, a layer of iron oxides was deposited, followed by a layer of iron-poor silicates in the aftermath. It took almost a billion years before aerobic bacteria evolved and broke the cycle. Think about that: for about a third of the entire time life has existed on this planet, it was stuck in this self-destructive loop. EDIT: What this story also shows is how much of Earth's geology is a result of the presence of life, and I recall reading articles of scientist trying to figure out if that could be used to detect the presence of life. Although I guess that measuring the chemical composition of the rocks on another planet would be even harder to measure than the atmosphere. [0] http://www.patheos.com/blogs/daylightatheism/2009/02/bands-of-iron/ http://www.patheos.com/blogs/daylightatheism/2009/02/bands-o... [1] https://en.wikipedia.org/wiki/Deep_time https://en.wikipedia.org/wiki/Deep_time