I’d say the most likely fate for Earth as we know it will come from within. Whether it is a nuclear war, climate catastrophe or collapse of civilisation, one only needs to look at history to see where the future may go. That’s why I believe humanity should establish a second biosphere to safeguard civilisation, culture and technology from our mistakes, sort of like seed banks.
Those man-made collapses would still yield the most life-friendly planet in the Solar System. We have a long time until the Sun turns into a red giant and our oceans boil away. Hopefully we will be out of the Solar System by then. There is always the Jovian system that might be more habitable as the Sun gets bigger.
Long before the Sun starts to die, Earth will be impacted by a large asteroid or comet, perhaps at the same scale of the impact event 65 million years ago. But life even survived then, and Earth returned to a habitable state. Again, if we had a second biosphere, human civilisation could return to Earth once it was habitable.
The one fate that worries me most is a small black hole wandering into the Solar System. Would we see it coming? Would it take out Earth, our Moon and Mars? Would we be here blissfully enjoying our existence one moment and then sucked into nothingness the next?
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