Sadly I think we squandered that chance. We had one cubic mile of oil. We're half way through it. The rest is being burnt off at record rates. This was a one time energy bounty.
We're mining ores with tiny percentages of what we want in them nowadays and at increasing energy cost.
We had a bounty of natural resources that we could have focused to get off this planet and become an interplanetary species. I suspect we will never get there as we've squandered these resources and overpopulated the planet beyond carrying capacity.
If you're waiting for a miracle solution, or believe alternatives will solve everything I recommend you study the principles of energy return on energy investment.
It makes me sad but I think we will never colonize other planets.
There's no such thing as an interplanetary species, barring some startling developments in physics. At the timescales it takes to travel to other solar systems, populations of colonists would be separated enough to speciate, especially given the radical differences in environment and the genetic drift of the early colony ships anyway.
Wouldn't it be quite feasible for humans even using current tech to go to the Moon, Mars, potentially moons of Jupiter or Saturn, and Venus? That would be interplanetary. Interstellar, perhaps not.
(I agree interplanetary would do a lot better with plausible tech of the next 50-100 years, but there's no reason not to get started today. Thank you, Elon Musk!)
Maybe, but wouldn't the same issues apply? After all, you still wouldn't have people going from planet to planet often enough for there to be much interbreeding. In any case, colonizing the rest of the solar system is fairly pointless since there aren't any other habitable planets.
To seriously colonize other planets would presumably mean we've solved the LEO lift problem (elevator? even easier on Mars, the Moon, etc.), have some nuclear-powered shuttles running around the planets, etc. At that point I think there would be at least as much contact between worlds as between continents in the 1500s. It might be largely one-way (Earth to Colonies), though.
Shipping reproductive material (either as information, or embryos, or frozen eggs/sperm) would also be fairly realistic.
The main reasons I can see for colonizing other planets are political (Earth is dominated by a certain kind of nation state, I'd happily live in a remote part of Earth if it would get me out from under that, as long as the right 5k people went with me...), or the spiritual/moral/whatever drive to do it because it can be done.
The fact that no one aside from small scientific installations have colonized Antarctica, which is orders of magnitude more habitable than the Moon or Mars, makes that claim rather doubtful.
