Extraterrestrial Life & the Fermi Paradox
Rare Earth Hypothesis
Argues that complex life requires an improbable conjunction of astronomical and geological circumstances, making simple microbial life plausibly common but complex or intelligent life exceedingly rare in the universe.
Proponents
Peter Ward, Donald Brownlee
Evidence For
Cites specific, argued-for requirements such as a large stabilizing moon, plate tectonics, a giant-planet "shield," and a long-term stable position in the galactic and circumstellar habitable zones.
Evidence Against
The discovery of thousands of exoplanets and of extremophiles thriving in extreme environments on Earth since 2000 have made some of its specific requirements look less restrictive than originally argued.
Real Sources
Transmissions
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