In planetary astronomy and astrobiology, the Rare Earth hypothesis argues that the emergence of complex multicellular life (metazoa) on Earth (and, as follows, intelligence) required an improbable combination of astrophysical and geological events and circumstances. The hypothesis argues that complex extraterrestrial life requires an Earth-like planet with the right conditions and that few if any such planets exist. The term "Rare Earth" comes from Rare Earth: Why Complex Life Is Uncommon in the Universe (2000), a book by Peter Ward, a geologist and paleontologist, and Donald E. Brownlee, an astronomer and astrobiologist.
The rare earth hypothesis is the contrary of the widely accepted principle of mediocrity (also called the Copernican principle), advocated by Carl Sagan and Frank Drake, among others. The principle of mediocrity concludes that the Earth is a typical rocky planet in a typical planetary system, located in a non-exceptional region of a common barred-spiral galaxy. Hence it is probable that the universe teems with complex life. Ward and Brownlee argue to the contrary: planets, planetary systems, and galactic regions that are as friendly to complex life as are the Earth, the solar system, and our region of the Milky Way are very rare.
By concluding that complex life is uncommon, the Rare Earth hypothesis is a possible solution to the Fermi paradox: "If extraterrestrial aliens are common, why aren't they obvious?"
Read more about Rare Earth Hypothesis: Rare Earth's Requirements For Complex Life, Rare Earth Equation, Advocates
Famous quotes containing the words rare, earth and/or hypothesis:
“What other words, we may almost ask, are memorable and worthy to be repeated than those which love has inspired? It is wonderful that they were ever uttered. They are few and rare indeed, but, like a strain of music, they are incessantly repeated and modulated by the memory. All other words crumble off with the stucco which overlies the heart. We should not dare to repeat these now aloud. We are not competent to hear them at all times.”
—Henry David Thoreau (1817–1862)
“We have in the service the scum of the earth as common soldiers.”
—Arthur Wellesley, 1st Duke Wellington (1769–1852)
“It is a good morning exercise for a research scientist to discard a pet hypothesis every day before breakfast. It keeps him young.”
—Konrad Lorenz (1903–1989)