Cometary Impacts and the Origins of Life on Earth

An interesting counterpoint to the role of comets and asteroids as bringers of destruction and extinction is the idea that these objects may also have brought the building blocks of life or even life in full-fledged form to Earth from outer space. Recent suggestions that meteorites, possibly of Martian origin, include exotic biotic materials has refocussed attention on the possible extraterrestrial origins of life. The idea that life arrived fully developed in the form of micro-organisms is often called "panspermia."

Probably the best known early exponent of panspermia in a scientific sense was the Nobel prize winner Svante Arrhenius (1859-1927). Arrhenius suggested that microbes could be hurled into near-planetary space by storms, and travel from planet to planet by radiation pressure (that is, comets or meteorites were not needed for transportation). Arrhenius is often credited with originating the idea of panspermia, although earlier scientists like William Thomson (Lord Kelvin) had already advanced the idea that life on Earth was seeded by meteorites.

In the 1950s, astronomer Otto Struve suggested that intelligent beings might have carried life from planet to planet, although not necessarily on purpose. This idea that we are descended from "garbage" left by alien travellers has informed a number of works of speculative fiction.

In recent years, physicists Fred Hoyle and Chandra Wickramasinghe have proposed not only that life originated from outer space in the distant past, but also that terrestrial evolution continues to be driven by the input of extraterrestrial genetic material. They also suggest that various historical pandemics were caused by bacteria or virii delivered by comets. These proposals have been rejected by most other scientists. Stephen J. Senn outlines some of the reasons why from an epidemiological point of view.

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Last modified by pib on May 12, 2009.