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How far can adaptation of living organisms go on planets orbiting extremely long-lived, but relatively stable stars?

Orange dwarf stars can live several times longer than stars like the Sun, but at the same time, are not as active or radioactive as red dwarfs. Ordinary Earth-like planets may well revolve around them on which life can exist for more than two or three billion years from its inception before the planet becomes too hot as the star transforms into a red giant. Such planets could live at least ten or twenty billion years.

Assumptions:
If we assume that meteorites will not fall on this planet so often or supervolcanoes erupt, and some civilization will not arrange a mass extinction, then how fart can local life can evolve?

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    $\begingroup$ "How far, in your opinion, can [something] go on [...] [in] ten or twenty billion years?" I would say that it could go on very far indeed, at least a few thousand miles. Maybe even ten thousand miles. Or about twenty thousand kilometers, metric. Or about four thousand parasangs, as the ancients would have reckoned really long distances. Or about five thousand leagues, as Jules Verne would say. (He was a visionary. His Nautilus famously went Twenty Thousand Leagues Under the Seas. But my opinions are rather more pedestrian.) In other words, what is the unit of measurement for how far? $\endgroup$
    – AlexP
    May 31 at 17:24
  • $\begingroup$ I mean, what can happen to the biosphere of a typical Earth–like planet with oxygen-breathing carbon-based life if we assume that this biosphere will exist in stable conditions without mass extinctions for 10-20 billion years? $\endgroup$ May 31 at 17:33
  • $\begingroup$ Are you asking the limits of evolution given sufficient time, or specifically how the pattern of evolution in an orange dwarf system is likely to shift over time? Either one is very broad, and almost exclusively the realm of speculation (but especially the first). $\endgroup$
    – DWKraus
    May 31 at 17:37
  • $\begingroup$ in this case, the first option is meant — what can the biosphere of a typical Earth-like planet turn into (in this case, local living beings can be considered as terrestrial anahogs) if they continue to interact with each other for so long without any mass extinctions that can have a significant external impact. $\endgroup$ May 31 at 17:44
  • $\begingroup$ We don't know. Earth has never ever had stable conditions for more than maybe a few million years. What with continents moving around, mountains rising, oceans opening and closing, ice ages coming and going, Milankovitch cycles cycling, and so on. In the last 500 million years we've had five all-caps MAJOR extinction events, plus the much older Great Oxidation Events, when the advanced civilization of algae polluted the air with a poisonous gas killing almost all other life forms. One of them was due to a collision with a moderately large asteroid. $\endgroup$
    – AlexP
    May 31 at 17:44

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Not As Much As You Might Think:

Time gives chance opportunity to do its evolutionary thing. But lots of factors can affect this as well. Your planet might be filled with frighteningly efficient competitive organisms - or be not be all that much more sophisticated in biology than Earth. Or it could be long dead.

First, your radiation is lower. This slows down random mutation. Lower mutation means slower change. Stable geology similarly reduces harmful, irregular mutagens oozing out of the mantle or bubbling up from deposits deep underground. All that slows evolution.

Second, disasters stir up opportunities for change and new organisms. If not for the K-T Dino killer, large dinosaurs might still rule. If not for the even bigger (likely volcanic) Permian extinction, dinosaurs might never have had a chance to compete with the dominant animals that came before. So without apocalypse to stir the pot, evolution may stall out on your world. It sounds like even the weather might be stable and temperatures could shift slowly, giving even poorly adapted creatures time to adapt and maintain their status in the ecology.

But there may also be limits to the life of your planet. As the core of the world cools and the planet isn't protected from radiation by a magnetic field, the atmosphere and seas may slowly be ablated off the planet. The slow shift of the output of the star might move the world out of the habitable zone and it could just freeze or cook. A nearby supernova might simply kill everything. The odds of a supernova probably go up with time. An intelligent creature from another world might come by and casually destroy the local life for stuff more like them.

There is one upside to evolution here, and that is the possibility that bigger metabolic adaptations in highly conserved functions would have time to occur. The rise of free oxygen production was one such event that transformed Earth, and the evolution of fungi that could consume wood sort-of ended the carboniferous period. Metabolic changes we haven't even considered for life might evolve here that take advantage of processes we haven't considered for life. This COULD mean that everything gets more efficient, OR that a super-bacteria kills and consumes all life like a "grey ooze" scenario.

Of course, all this is speculation. We really don't know what would happen for sure. Find one of these, and get back to me in 20 billion years.

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