But I would presume in such conditions, the Oort objects would mostly have been fully perturbed out of position well before the dawn of evolution, much as most minor bodies have been cleaned out of the solar system (except the asteroid belt) by frequent influence of the planets. Alternatively, it may be there are random unattached bodies that impact from time to time, as the neighbour stars make a coherent orbiting cloud impossible. Certainly, no stable cloud.
Is that really a Great Filter? Consider that most of the oxygen produced would combine with dissolved metals (mostly iron) so wouldn’t be a hazard to life. There was a huge amount of dissolved iron at the time and the resultant iron oxide makes up a thick layer of what is now iron ore. Yes, many species of one-celled organisms did not survive, but such organisms have a lot of variability, so I don’t think it’s at all surprising that some survived. Especially the ones emitting the oxygen, since if they couldn’t survive it, it shuts down the whole thing at the start.
True, but close approaches of about that distance occur regularly in the non-core parts of the Galaxy. For example, just 70,000 years ago, Scholz's Star - Wikipedia made a close (.82 lightyears) flyby of the Sun. Another example from the Solar neighborhood is Luyten's Star - Wikipedia, which had a 1.12 ly approach to Procyon just 600 years ago.
The Oort Cloud objects that Scholz’s Star disturbed will not come into the inner solar System for something like a million years. It’s not something to worry about.
Why wouldn’t they survive? I presume, the oxygen release happened over a geological time frame, giving life ample time to adapt to to increasing levels of oxygen. The question is whether the geology allows for the sequestering of the matching carbon into the crust so as to allow free oxygen to dominate.
In our world, the vast majority of life didn’t survive. It was the worst mass extinction event in our planet’s history. It’s not hard to see how “almost everything dying” could slip over into “absolutely everything dying”.
Something like one in ten species survived. That’s a significant bottleneck event but from a survival of life perspective not “almost everything” … Archea and bacteria can evolve and spread quickly.
It wasn’t just that; the world went through an intense glacial period and it’s quite possible it could have permanently frozen.
Also, evolution is contingent. It can only select for an adaptation if some random mutation provides it, and if no such mutation occurs the adaptation can’t happen.
A billion life forms (probably an underestimate) and a hundred million years, what are the odds nothing evolves to tolerate and use an oxygen rich environment? But isn’t the whole point of the oxygenation process simply that life evolved that did create free oxygen?
Look at the incredible range of life that exists on earth today - adaptions to everything from freezing temperatures to aquatic ocean vents, Producing and feeding on a vat array of organic substances. The only real debate is whether the existence of a large moon (and hence tides) was a contributor to the level of life we find today.
Perhaps the great filter is actually social. If we do not outgrow war in the next few centuries, we will, at some point, wipe out civilization with nuclear weapons.
Yup, that’s a common guess (probably the most common one for a “we haven’t passed the filter yet”).