[matroosberg]

It almost certainly is the most habitable planet for life as we know it today because we and our environment co-evolved to match the conditions. Just because 2/3 of the planet (not sure how you arrived at the number / what parts are in the denominator) doesn't meant it is meaningless to what allows us to live here (e.g., oxygen and food supply from the oceans).

OTOH I disagree with the notion that we have to have a full grasp on how to sustain us on this planet before we can make other planets inhabitable for us. I think there are things we will only learn if we try. I am not saying that trying right now is feasible, though.

[echelon]

I agree that we have an extremely low probability of finding a planet that could host our biology as well as Earth's given that we evolved here, but I refute your absolute claim.

Invasive species don't co-evolve to exploit the ecosystems they stumble upon. They happen upon a ecological space where there are incredibly low hanging fruit that they are better equipped at taking advantage of. Imagine space-faring humans stumbling upon a world where the oceans resemble that of the Earth's as they once existed in the 1500's--a world densely populated with an abundance of marine life, ripe for harvesting.

While there is some probability that biochemistry is not 100% universal (ie. alien metabolites could be toxic to humans or cause an immune response), I imagine there are scenarios where the same set of molecules and polymers are used. The principles of biochemistry are going to be similar in a lot of places in terms of how energy is exploited and harnessed.

I think it's incredibly more likely that humans will never be interstellar travelers en masse than to say that Earth is the optimal naturally occurring human habitat in the universe. As far as we know there is an infinite space full of limitless planets. Plenty of biological solution space with which to theoretically work / exploit.