This is context. The essayist explains how Earth’s population is growing to introduce a possible solution—colonizing other planets. This context helps us understand the essayist’s main point: colonizing other planets won’t solve overpopulation in the long term, only temporarily.

The essayist doesn’t make this claim. The essayist argues that if Earth's population keeps growing, one proposed solution may not be enough. However, the essayist doesn’t say for sure that Earth's population will grow this way or that overpopulation will “probably” be a problem.

This is a premise. The fact that Earth will be just as crowded again after half the population moves to another planet supports the main conclusion that colonizing other planets is only a temporary fix for overpopulation. It explains why this solution won’t help in the long term.

This is an assumption the essayist makes. The essayist assumes that Earth's population will keep doubling, even after some people hypothetically move to Mars. If this assumption is true, the essayist argues that colonizing other planets will only temporarily fix overpopulation.

This accurately states the main conclusion. The essayist disagrees that colonizing other planets will solve Earth's future overpopulation, believing it would only be a temporary solution for such overcrowding because the growing population will eventually replace those who leave.