EXTflHTEHRESTRIHLS AND UF05 129
The most vivid illustration of the importance of carbon was the famous experiment conducted by Stanley Miller and Harold Urey in
1953, which showed that the spontaneous formation of life may be a
natural by-product of carbon chemistry. They took a solution of ammonia, methane, and other toxic chemicals that they believed were
found in the early Earth, put it in a flask, exposed it to a small electrical current, and then simply waited. Within one week they could see
evidence of amino acids forming spontaneously in the flask. The electrical current was sufficient to break apart the carbon bonds within
ammonia and methane and then rearrange the atoms into amino
acids, the precursors of proteins. In some sense, life can form spontaneously. Since then, amino acids have been found inside meteorites
and also in gas clouds in deep space.
Third, the fundamental basis of life is the self-replicating molecule
called DNA. In chemistry, self-replicating molecules are extremely
rare. It took hundreds of millions of years to form the first DNA molecule on Earth, probably deep in the oceans. Presumably, if one could
perform the Miller-Urey experiment for a million years in the oceans,
DNA-like molecules would spontaneously form. One likely site where
the first DNA molecule on Earth might have occurred early in the
Earth's history is near volcano vents on the ocean bottom, since the activity of the vents would create a convenient supply of energy for the
early DNA molecule and cells, before the arrival of photosynthesis and
plants. It is not known if other carbon-based molecules besides DNA
can also be self-replicating, but it is likely that other self-replicating
molecules in the universe will resemble DNA in some way.
So life probably requires liquid water, hydrocarbon chemicals, and
some form of self-replicating molecule like DNA. Using these broad
criteria one can derive a rough estimate for the frequency of intelligent
life in the universe. In 1961 Cornell University astronomer Frank
Drake was one of the first to make a rough estimate. If you start with
100 billion stars in the Milky Way galaxy, you can estimate what fraction of them have stars like our sun. Of these, you can estimate what
fraction have solar systems revolving around them.
The most vivid illustration of the importance of carbon was the famous experiment conducted by Stanley Miller and Harold Urey in
1953, which showed that the spontaneous formation of life may be a
natural by-product of carbon chemistry. They took a solution of ammonia, methane, and other toxic chemicals that they believed were
found in the early Earth, put it in a flask, exposed it to a small electrical current, and then simply waited. Within one week they could see
evidence of amino acids forming spontaneously in the flask. The electrical current was sufficient to break apart the carbon bonds within
ammonia and methane and then rearrange the atoms into amino
acids, the precursors of proteins. In some sense, life can form spontaneously. Since then, amino acids have been found inside meteorites
and also in gas clouds in deep space.
Third, the fundamental basis of life is the self-replicating molecule
called DNA. In chemistry, self-replicating molecules are extremely
rare. It took hundreds of millions of years to form the first DNA molecule on Earth, probably deep in the oceans. Presumably, if one could
perform the Miller-Urey experiment for a million years in the oceans,
DNA-like molecules would spontaneously form. One likely site where
the first DNA molecule on Earth might have occurred early in the
Earth's history is near volcano vents on the ocean bottom, since the activity of the vents would create a convenient supply of energy for the
early DNA molecule and cells, before the arrival of photosynthesis and
plants. It is not known if other carbon-based molecules besides DNA
can also be self-replicating, but it is likely that other self-replicating
molecules in the universe will resemble DNA in some way.
So life probably requires liquid water, hydrocarbon chemicals, and
some form of self-replicating molecule like DNA. Using these broad
criteria one can derive a rough estimate for the frequency of intelligent
life in the universe. In 1961 Cornell University astronomer Frank
Drake was one of the first to make a rough estimate. If you start with
100 billion stars in the Milky Way galaxy, you can estimate what fraction of them have stars like our sun. Of these, you can estimate what
fraction have solar systems revolving around them.