El Calendario Cósmico - cosmos possible worlds parte 3

Cyanobacteria were the dominant life form on this planet, wreaking havoc wherever they went, changing the landscape, the water and the skies. This was 2.3 billion years ago, or late October on the cosmic calendar. But the cyanobacteria shared the planet with other beings, the anaerobes, life forms that had come of age before cyanobacteria had begun to pollute the Earth with oxygen. For the anaerobes, oxygen was poison. But the cyanobacteria wouldn't stop loading up the atmosphere with the stuff. For the anaerobes, and nearly all of the other life on Earth, it was an oxygen apocalypse. The lone survivors among the anaerobes were those who sought refuge at the bottom of the The cyanobacteria acted like oxygen pumping machines. They continued in overdrive, and 400 million years later, they brought about an even more radical change to the planet. Remember those serpentinized rocks at the bottom of the sea that were cranking out hydrogen and methane? Methane is a powerful greenhouse gas, and back then, it was the main thing keeping the planet warm. But once again, the oxygen produced by life shook things up. It gobbled up the methane, producing carbon dioxide, a much less potent greenhouse gas, meaning it was not as efficient at trapping heat in Earth's atmosphere. Earth's temperature began to plunge. Life, the escape artist, busted out of the icy death grip that entombed the planet. The corpses of dead bacteria left behind a planet-wide reservoir of carbon dioxide. Volcanoes pumped the carbon dioxide in huge quantities into the atmosphere, warming the planet and melting the ice. Over the next billion years, life in the rocks continued their elaborate dance, taking the planet through freezes and thaws. Then, 540 million years ago, something wondrous happened. Life, which had been all about microbes and simple multicellular creatures, suddenly took off in what's called the Cambrian Explosion. Life grew legs, eyes, gills, teeth, and rapidly began to evolve the forms of its stunning diversity. We don't yet know what it was that allowed life to diversify so dramatically, but we have some plausible theories. It could have been all those calcium minerals in the seawater that came from the volcanoes. Life had grown a backbone and put on a shell. It had found a way to collaborate with the rocks to make its own armor. Now life could grow larger and venture forth into new territories. Or maybe it was the protection afforded by the canopy built by the cyanobacteria. The oxygenation of the atmosphere created the ozone layer. This made it possible for life to break out of the safety of the oceans and inhabit the land without being assaulted by the sun's deadly ultraviolet rays. For billions of years, all life could do was ooze. Now, life began to swim, run, jump, and fly. Life, the escape artist, had gotten so good at wriggling out of every confine, no prison on Earth could hold it. And there will come a day when life would even escape from Earth. Life will not be contained.