People are part of a vibrant ecosystem. As omnivores, we eat most anything. Our food contains some useable energy that powers our bodies. While body size and activity effect the required amount of energy, a reasonable estimate for the base amount is 1e7 Joules/day.

Currently, the Earth can provide everyone with sufficient dietary energy. In special circumstances, people try to live apart from the natural ecosystem. The Biosphere project and the ISS are great examples of such endeavours. Another is a doomsday shelter proposed for Kansas. The shelter claims to allow for 70 people to securely and separately live indefinitely at today’s living standard. Food comes from an interior fish and vegetable farm. But, has the complete life cycle been replicated. What do the fish eat? What fertilizes the vegetables? How is photosynthesis activated? Which detrivores cycle the waste back? While this shelter seems ideal, what proof is there on its claim to be a self-sustaining locale that can act like a miniature Earth?

Apart from dietary needs, people today also expect large amounts of energy for their technology needs. At 1GJ/person/day or 10381 W/person/day, the shelter requires a 1MW generation system. Without a vast reservoir of fossil fuels at-hand, the shelter could never meet this expectation.

Miniature Earths, no matter where the location in the universe, would need to mimic a very complex ecosystem to support human life. Further, it would have to compliment the entire technology largess that people have come to expect. As the ISS shows, this is no small feat no matter how capable and erudite the people.