"*Scattering the Seeds of
Life*<http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=3028&mode=thread&order=0&thold=0>
*[image: Meteors, Comets and
Asteroids]*<http://www.astrobio.net/news/modules.php?op=modload&name=News&file=index&catid=&topic=8>
*Summary* (Feb 05, 2009): Some astrobiologists think life may have arrived
on Earth inside a comet or meteorite. Calling this process "Panspermia" is
misguided, says a historian who has studied the evolution of thought about
life's origin.
------------------------------
Scattering the Seeds of Life*By Leslie Mullen <l_mul...@earthlink.net> *
Meat left out too long will eventually bear maggots or mold. These days we
know the maggots hatch from fly eggs and the mold grows from spores that
were carried in the air, but in the past the fuzzy growth and wriggling
white bodies were proof that whole organisms could spontaneously arise from
rotten meat or certain other types of inanimate matter.
Louis Pasteur in his laboratory. Painting by Albert Edelfeldt (1885).
In the early 1860s, the French chemist Louis Pasteur proved that such
"spontaneous generation" did not occur, but instead the air itself was full
of bacteria, spores, and other forms of reproducing life. Across the
Channel, in 1859, Charles Darwin published "On the Origin of Species," which
promoted the notion that life forms were ever-changing, evolving into new
species over the eons.
Pasteur's experiments and Darwin's theory led to opposing conclusions
regarding the origin of life on Earth. Pasteur claimed that his work lent
support to the belief that God created life. Just as life could not arise
spontaneously from inanimate matter, the first life on the early Earth could
not have arisen without the aid of a divine creator. Yet Darwin's theory of
life evolving over time implied that the first life on Earth could have
evolved naturally from inanimate matter.
Toward the end of the 19th century and the beginning of the 20th century, as
scientists were learning about the genetic and biochemical complexity of the
cell, confusion about the origin of life grew. One way around the problem
was to say that life had never emerged, but that it had always been an
inherent part of the universe.
"The universe and matter were regarded then as eternal," says Iris Fry, a
historian of biology at the Israel Institute of Technology and author of
"The Emergence of Life on Earth: A Historical and Scientific Overview."
"Life was also claimed to be eternal. Life always existed and didn't have to
arise from matter. In this way, the problem of the origin of life was
explained away."
Evaporating water ice particles are in the tail and surround the nucleus
of Comet Hyakutake. Some scientists believe comets spread the organic
materials necessary for life's origin.
Photo Credit: *NASA*
Fry points to scientists such as Hermann von Helmholtz in Germany, Lord
Kelvin in England, and Svante Arrhenius in Sweden, who promoted the idea of
sperms of life wandering the universe and taking root in any planet with the
appropriate conditions. This idea of the seeds of life being everywhere
became known as the Panspermia hypothesis ("pan" being the Latin root
meaning "all"). Helmholtz, Kelvin, and others suggested that life traveled
to planets within meteorites. Arrhenius and others claimed that seeds of
life, protected as spores, could be pushed toward planets by solar
radiation.
Fry says that the current usage of the term "Panspermia" ignores the history
of ideas on the origin of life and the specific meaning of this term.
"Certainly scientists today do not believe that the universe is eternal,
they do not believe that life is eternal," says Fry. "The cosmology changed.
People began to realize that the universe had a beginning and that it was
expanding, so this whole idea of eternity lost ground."
Fry says that the notion of eternity was used in the past to promote a
philosophy that life and matter were separate unbridgeable entities.
However, most scientists today agree that life arose from non-living matter.
"Scientists who believe that life might have arrived on Earth from space by
meteorites or comets do not doubt that this life emerged from matter at a
certain point in time on another planet," says Fry.
Dark molecular clouds of gas and dust are located within the Carina
Nebula. Scientists have detected molecules important for life within such
clouds.
Photo Credit: *NASA, ESA, N. Smith (U. California, Berkeley) et al., and The
Hubble Heritage Team (STScI/AURA)*
The term "Transpermia" is used now by several scientists to describe the
transfer of life from planet to planet. Fry prefers this usage of
Transpermia to Panspermia because it avoids the confusion with the old
meaning.
Some scientists who study organic molecules in space have used the term
Panspermia to describe the delivery of these molecules to planets like
Earth. "This is neither Panspermia nor Transpermia, because it is not the
transport of life, but just the transport of what might have served as the
building blocks for life," says Fry.
While many of the molecules important for life have been detected in space,
and meteorites and comets possibly could contain life itself, that doesn't
necessarily mean life came to Earth from space. While some experiments
suggest the transfer of life from one planet to another is theoretically
possible, life would have to endure quite a lot to get here. The conditions
in space are extremely hostile to Earth-based life, which tends to die when
exposed to an airless vacuum and extremes of temperature and radiation.
Also, Earth's atmosphere acts as a barrier to life falling in from space.
Recent tests <http://www.astrobio.net/news/article2889> conducted by
European scientists have found that microbial life can not survive the fiery
conditions of atmospheric entry. Some scientists even question whether organic
material <http://www.astrobio.net/news/article2138> delivered by comets and
meteorites was necessary for life's origin, since the early Earth may have
had plenty of organic material of its own.
As for what she believes, Fry says it is an open question whether or not
life came to Earth from space.
"When the Earth formed, the solar system was undergoing this accretion
process, and there was exchange of material between the planets, the heavy
bombardment period where asteroids hit the Earth," she notes. "It could well
have been that life started on Mars, for instance, and then reached Earth.
Still, even though it's a possibility, I don't see why life couldn't have
started here." "
http://www.astrobio.net/news/index.php?name=News&file=article&sid=3028
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