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.
- Center for Mars Exploration
from NASA offers a number of links about the suggestion that a
meteorite of possible Martian origin contains relics of early
biogenic activity. Includes the text of the original article from
the journal Science.
- Cometary Delivery Of Organic Molecules To The Early Earth
by Christopher F. Chyba, Paul J. Thomas, Leigh Brookshaw, and Carl
Sagan, was originally published in the journal
Science, v.249, pp. 366-373. Chyba et al discuss
the idea "that Earth accreted prebiotic organic molecules important
for the origins of life from impacts of carbonaceous asteroids and
comets during the period of heavy bombardment 4.5 Gyr to 3.8 Gyr
ago." Chyba, Thomas, and Christopher P. McKay have also edited a
book on this subject, entitled Comets and the Origin and
Evolution of Life. Springer Verlag, 1996. ISBN
- Comets, Contagion And Contingency
by Stephen J. Senn discusses the ideas of Hoyle and Wickramsinghe.
This is a paper in Adobe Acrobat PDF format.
- Cosmic Ancestry
by Brig Klyce is an entire web site devoted to panspermia,
primarily of the Hoyle/Wickramasinghe type.
- Did Earth's Life Originate on Mars?
by Paul Lutus offers a non-technical discussion of the suggestions
put forth in 1996 by NASA scientists that a meteorite believed to be
of Martian origin contains remains of ancient cellular life of
- Exobiology Branch
of NASA offers a wide variety of information about current research
into extraterrestrial life, including the idea that comets or
meteors delivered prebiotic materials to Earth.
- Exobiology of Comets and Meteorites: Annotated Bibliography
by Norman Redington and Karen Rae Keck offers a nice list of
references about panspermia and related ideas.
- Life's Far-Flung Raw Materials
by Max P. Bernstein, Scott A. Sandford, and Louis J. Allamandola
appeared in the July 1999 issue of Scientific American.
The authors develop the idea that life on Earth was seeded by raw
materials from space.
describes the discovery mission by NASA which flew a probe by a
comet (Comet Wild 2) and returned with a sample of cometary material
for detailed analysis. Analysis of the returned sample will help
answer questions about the possibility of cometary origins for
prebiotic and biotic materials here on Earth.
- Studying Life's Origins by Recreating the Early Solar System
by Edna DeVore discusses the possible role of comets in
jump-starting life on Earth.
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Last modified by
pib on May 12, 2009.