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Given how dramatically our civilization has changed in the last couple of centuries, I have no idea what lies ahead. Certainly, if we are not careful, we could be heading for the Great Filter. But assuming we can overcome the short term effects of environmental damage we have caused before a catastrophe, the idea should be to colonize the Solar System first. We should get moving immediately - it's get to see the likes of Elon Musk and Stephen Hawking heavily push this agenda.

If we can colonize the solar system, the next step would be nearby star systems, of course. I can't even begin to imagine what kind of resources that would take...

It is interesting to note that the applications that will help us survive in space and on hostile (in terms of environment) worlds can also be put to use in our oceans.

But I agree with you, and with Musk and Hawking; one of our higher priorities should be to spread ourselves throughout the solar system, and to prepare for the next step into the galaxy.

One other thing we should be aware of in terms of dangers to our species survival; humans have a tendency to breed beyond our ability to support ourselves. This amplifies the dangers you spoke of.