By Jane Van Susteren, XRI Lead Exobiologist
Exploring a different biosphere means reevaluating many of the things biology takes for granted. Confining our searches to relatively Earth-similar planets means that potential organisms will very likely have some similarities—but if there is life, we expect it to be totally unlike what we are familiar with.
A series of accidents and quirks of geology, climate, and geography made Earth's organisms what they are today. Without the high carbon dioxide levels during the Devonian (probably caused by volcanoes), land plants would not have become gloriously diverse. The Permian-Triassic extinction event (and probable asteroid impact) allowed seed-bearing plants and mammals to proliferate and the first endosymbiotic events seem to be pure fortuitous accidents.
We are assuming that there will be some constants in life on a foreign planet. First and foremost, life will need to obtain and consume some sort of energy. Whether the source of the energy is heat from the planet's core, chemical reactions from the rocks, nutrients gained from consuming other life forms, or good old-fashioned photosynthesis, organisms must somehow harvest energy to grow and reproduce. We expect amazing discoveries in how life finds a way—life forms could even potentially have tiny windmills to harvest energy from the air itself!
