probably in local hot springs. Earth was lucky that it was close enough to the sun and had enough volcanic activity releasing greenhouse gases to let it eventually escape the snowball state or else we might be frozen still, and not get liquid oceans until some time in the future when our ever-heating sun finally melts through the ice. If it had been slightly farther from the sun, CO 2 could have frozen at the poles as dry ice, robbing Earth of the snowball escape and making it more like Mars. Surface life might have died completely.
The Earth with its new oxygen atmosphere was a bizarre place, at least in terms of what was happening, or not happening, to life. It is clear that aerobic respiration, our biochemistry that allows us to breathe oxygen, could only have evolved after oxygen was present. There had to have been a time gap between the presence of oxygen and the first organisms capable of breathing it. In fact, evolution would have immensely favored any organism that could use oxygen, since no other molecule lets the chemical reactions we call life take place faster, with more precision, and liberate as much energy as those where oxygen is used.
The time gap between the evolution of oxygen release and the presence of organisms in the biosphere that could breathe it is identifiable in the geological record. The cyanobacteria that suddenly found themselves in a world no longer covered in ice would quickly have invaded the new and warm surface waters of every ocean, and because the amount of land area more than 2.2 billion years ago was vastly less than now, and the planetary ocean would have had millions of years to load up on raw nutrients from hydrothermal vents, they would havemultiplied to numbers almost incomprehensible, rapidly increasing the amount of oxygen. They would have been floating in the marine ecosystem on shallow subsurface horizons where light could reach, and even on what little land area was present. While these organisms would be madly excreting this molecular oxygen, they would also be rapidly depleting the carbon dioxide that had built up in the air during the snowball Earth event they caused, producing a wealth of hydrocarbons in the ocean environment. For every molecule of O 2 released by photosynthesis, one atom of carbon is incorporated into the stuff of life. Today, light hydrocarbons of that sort are eaten by oxygen-breathing organisms and converted back into carbon dioxide. But if organisms had not yet evolved the ability to breathe oxygen, the question arose as to where all of this floating organic material would have gone. There would have been so much of it that there would have been major changes to the surface of the Earth’s chemistry and its oceans and air.
Oil and oxygen when mixed together in the air form an explosive cocktail; a single spark of lightning would cause a reaction to go without stopping. But oil dispersed in water, as little particulates, can only be degraded by the action of microbes. Without efficient recycling, Earth should have experienced a huge imbalance in the carbon cycle. In particular, a large amount of oil should’ve been produced, and an equal amount of oxygen should’ve been pumped into the atmosphere. At this time, we do have evidence for a massive oxidation event at 2.1 GA; it formed one of the world’s largest deposits of pure hematite (Fe 2 O 3 ) iron ore—the Sishen mine in South Africa. 15 Earth’s atmosphere must have been supercharged with oxygen at that time, to levels not encountered since, and probably impossible to reach without some deviant biosphere driving it there. If planets orbiting other stars went through the same process, the hyperbaric oxygen in their atmospheres would be waving a spectral flag proclaiming, “We are here, and we solved the photosynthesis problem!”
In fact, the record of carbon isotopes for the period of time between 2.2 and 2.0 billion years ago is so wildly out of balance that geochemists have given it its
The Earth with its new oxygen atmosphere was a bizarre place, at least in terms of what was happening, or not happening, to life. It is clear that aerobic respiration, our biochemistry that allows us to breathe oxygen, could only have evolved after oxygen was present. There had to have been a time gap between the presence of oxygen and the first organisms capable of breathing it. In fact, evolution would have immensely favored any organism that could use oxygen, since no other molecule lets the chemical reactions we call life take place faster, with more precision, and liberate as much energy as those where oxygen is used.
The time gap between the evolution of oxygen release and the presence of organisms in the biosphere that could breathe it is identifiable in the geological record. The cyanobacteria that suddenly found themselves in a world no longer covered in ice would quickly have invaded the new and warm surface waters of every ocean, and because the amount of land area more than 2.2 billion years ago was vastly less than now, and the planetary ocean would have had millions of years to load up on raw nutrients from hydrothermal vents, they would havemultiplied to numbers almost incomprehensible, rapidly increasing the amount of oxygen. They would have been floating in the marine ecosystem on shallow subsurface horizons where light could reach, and even on what little land area was present. While these organisms would be madly excreting this molecular oxygen, they would also be rapidly depleting the carbon dioxide that had built up in the air during the snowball Earth event they caused, producing a wealth of hydrocarbons in the ocean environment. For every molecule of O 2 released by photosynthesis, one atom of carbon is incorporated into the stuff of life. Today, light hydrocarbons of that sort are eaten by oxygen-breathing organisms and converted back into carbon dioxide. But if organisms had not yet evolved the ability to breathe oxygen, the question arose as to where all of this floating organic material would have gone. There would have been so much of it that there would have been major changes to the surface of the Earth’s chemistry and its oceans and air.
Oil and oxygen when mixed together in the air form an explosive cocktail; a single spark of lightning would cause a reaction to go without stopping. But oil dispersed in water, as little particulates, can only be degraded by the action of microbes. Without efficient recycling, Earth should have experienced a huge imbalance in the carbon cycle. In particular, a large amount of oil should’ve been produced, and an equal amount of oxygen should’ve been pumped into the atmosphere. At this time, we do have evidence for a massive oxidation event at 2.1 GA; it formed one of the world’s largest deposits of pure hematite (Fe 2 O 3 ) iron ore—the Sishen mine in South Africa. 15 Earth’s atmosphere must have been supercharged with oxygen at that time, to levels not encountered since, and probably impossible to reach without some deviant biosphere driving it there. If planets orbiting other stars went through the same process, the hyperbaric oxygen in their atmospheres would be waving a spectral flag proclaiming, “We are here, and we solved the photosynthesis problem!”
In fact, the record of carbon isotopes for the period of time between 2.2 and 2.0 billion years ago is so wildly out of balance that geochemists have given it its
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