The biology on this globe is carbon-based. Some have speculated that there could be silicon-based forms of biology elsewhere in this universe. There yet could be plasma-based biology. There could be incorporeal biology. There could be other probabilities.
Source: tatoeba (9085653)
In his book Star Maker, Olaf Stapledon speculated that some advanced civilizations elsewhere in this universe do not survive their experimentations with technology of advanced physics.
Source: tatoeba (10601889)
They reduced Hegel to half-sheets of paper, suggested profanely various readings for Petronius, speculated without reverence on the darker habits of mankind from Aristotle to the Junior Prior.
Source: tatoeba (11591811)