Nobody knows how life on Earth began, but the primordial
soup likely got a lot of its ingredients from space.
Scientists have discovered concentrations of amino acids in
two meteorites that are more than ten times higher than levels previously
measured in other similar meteorites.
Amino acids are organic molecules that form the backbone of
proteins, which in turn build many of the structures and drive many of the
chemical reactions inside living cells. The production of proteins is believed
to constitute one of the first steps in the emergence of life. Meanwhile, meteorites
found on Earth are typically chunks of material created in the solar system's
youth.
So the finding suggests that the early solar system was far
richer in the organic building blocks of life than scientists had thought. The
researchers speculate that rocks from space may have spiked Earth's primordial
broth.
It's an argument that's been made before.
But the prevalence of amino acids strengthens the reasoning.
Scientists already knew amino acids could have formed in
some environments on the early Earth, but the presence of these compounds in
certain meteorites has led many researchers to look to space as a source.
The meteorites used for the study were collected in Antarctica
in 1992 and 1995 and held in the meteorite collection at the NASA Johnson Space
Center in Houston. Researchers took small samples from three rare CR chondrites,
which date from the time of the solar system's formation. The rocks likely came
from an asteroid that was long ago shattered.
"The amino acids probably formed within the parent body
before it broke up," said Conel Alexander of the Department of Terrestrial
Magnetism at the Carnegie Institution. "For instance, ammonia and other
chemical precursors from the solar nebula, or even the interstellar medium,
could have combined in the presence of water to make the amino acids. Then, after
the break up, some of the fragments could have showered down onto the Earth and
the other terrestrial planets. These same precursors are likely to have been
present in other primitive bodies, such as comets, that were also raining
material onto the early Earth."
The study will be detailed in the journal Meteoritics and
Planetary Science.
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