existing (anaerobic) life. Today you call that poisonous gas “oxygen” and breathe it. The rise of oxygen also depleted the atmosphere of methane, a greenhouse gas, and froze your planet from pole to pole – your star was a good deal cooler then – so photosynthesis stopped as temperatures dropped, and the only life which survived was clustered around volcanic vents on the sea bottoms. The ice over the oceans prevented volcanic CO2 from being taken up by the seas, and ultimately this CO2 warmed the planet and melted the ocean ice by rising to more than 10% of the atmosphere. The greenhouse effect is the biggest deal, by far, when it comes to wiping out complex life. So, it’s a bit of a pity th at you have made overloading the seas and sky with CO2 your “big socio - economic experiment.” Screwing around with CO2 and methane levels, even in small percentages and over a short time span, is analogous to monkeys fighting over hand grenades: there is a most-probable outcome. And here is one more alien opinion for you to mull over: you’ve been lucky . When looking back at your world’s history, it seems that mass extinctions are not just normal, but in your case beneficial, since — ta daa! — they were part of the chain of events which eventually produced you humans. However, the continuity of life should not be taken for granted. It may seem to you inevitable that you should have come into existence, but it was not. You are experiencing “survivorship bias” by looking backwards and seeing that none of the mass extinctions ended all life, because a conscious being can only evolve from pre-existing life. On all worlds, mass extinctions eventually take all life . Life began and was extinguished on Earth many times before conditions finally allowed your own ancestors’ quickening to survive and flourish. My people believe it also began in the seas of Venus, whose species long looked through clear blue skies to the stars on a planet which was Earth’s twin, seeing among them the pale blue dot which housed your ancestors. There are a lot of barren rocks in this universe, and perhaps very few living water worlds. When you wish upon the evening star Venus, you’re wishing on a forme r watery Earth, now a furnace-world, devoid of life, the effect of accumulation of greenhouse gases. The Bottom Line: Since the rise of complex life, there have been five major planetary extinction events. We’ve started what may be the sixth.
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