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Wednesday, March 14, 2012
Meteorites Reveal Another Way to Make Life's Components
It appears that natural amino
acid generation is taking place in Space over both low temperatures and also
with high temperatures.Thus without any
contribution necessary on a planet, it appears that a wide range of amino acids
will be arriving anyway.
It turns out that our bias
against all that was simply an assumption founded on nothing.We live in a universe that must be filled
with available amino acids.
It also underlines the fact that
chemistry happens over a far wider range of temperatures that we were ever
comfortable with and with that a wide range of pressure.I would really like to know those ranges and
to determine just how much research has been done outside our natural comfort
range.Certainly a million questions
have been answered inside our comfort range.
It could well turn out that a
full tool kit arrives on planet in preparation for the self assembly of life in
the first bombardment and that happens on every planet. That is big enough to
Meteorites Reveal Another Way to Make Life's Components
by Bill Steigerwald for GoddardSpaceFlightCenter,
Greenbelt, MD (SPX) Mar 12, 2012
A meteorite analyzed in the study at its collection site in Antarctica.
Credit: Antarctic Search for Meteorites program, CaseWestern ReserveUniversity.
Creating some of life's building blocks in space may be a bit like
making a sandwich - you can make them cold or hot, according to new NASA research.
This evidence that there is more than one way to make crucial components of
life increases the likelihood that life emerged elsewhere in the Universe,
according to the research team, and gives support to the theory that a
"kit" of ready-made parts created in space and delivered to Earth by
impacts from meteorites and comets assisted the origin of life.
In the study, scientists with the Astrobiology Analytical Laboratory
Goddard Space Flight Center in Greenbelt, Md., analyzed samples from fourteen
carbon-rich meteorites with minerals that indicated they had experienced high
temperatures - in some cases, over 2,000 degrees Fahrenheit. They found amino
acids, which are the building blocks of proteins, used by life to speed up chemical
reactions and build structures like hair, skin, and nails.
Previously, the Goddard team and other researchers have found amino
acids in carbon-rich meteorites with mineralogy that revealed the amino acids
were created by a relatively low-temperature process involving water, aldehyde
and ketone compounds, ammonia, and cyanide called "Strecker-cyanohydrin
"Although we've found amino acids in carbon-rich meteorites
before, we weren't expecting to find them in these specific groups, since the
high temperatures they experienced tend to destroy amino acids," said Dr.
Aaron Burton, a researcher in NASA's Postdoctoral Program stationed at NASA Goddard.
"However, the kind of amino acids we discovered in these
meteorites indicates that they were produced by a different, high-temperature
process as their parent asteroids gradually cooled down." Burton is lead author of a paper on this discovery
appearing March 9 in Meteoritics and Planetary Science.
In the new research, the team hypothesizes the amino acids were made by
a high-temperature process involving gas containing hydrogen, carbon monoxide,
and nitrogen called "Fischer-Tropsch" -type reactions.
They occur at temperatures ranging from about 200 to 1,000 degrees
Fahrenheit with minerals that facilitate the reaction. These reactions are used
to make synthetic lubricating oil and other hydrocarbons; and during World War
II, they were used to make gasoline from coal in an attempt to overcome a
severe fuel shortage.
Researchers believe the parent asteroids of these meteorites were
heated to high temperatures by collisions or the decay of radioactive elements.
As the asteroid cooled, Fischer-Tropsch-type (FTT) reactions could have
happened on mineral surfaces utilizing
gas trapped inside small pores in the asteroid.
FTT reactions may even have created amino acids on dust grains in the
solar nebula, the cloud of gas and dust that collapsed under its gravity to
form the solar system. "Water, which is two hydrogen atoms bound to an
oxygen atom, in liquid form is considered a critical ingredient for life.
However, with FTT reactions, all that's needed is hydrogen, carbon
monoxide, and nitrogen as gases, which are all very common in space. With FTT
reactions, you can begin making some prebiotic components of life very early,
before you have asteroids or planets with liquid water," said Burton.
In the laboratory, FTT reactions produce amino acids, and can show a
preference for making straight-chain molecules. "In almost all of the 14
meteorites we analyzed, we found that most of the amino acids had these
straight chains, suggesting FTT reactions could have made them," said Burton.
It's possible that both Strecker and FTT processes could have
contributed to the supply of amino acids in other meteorites. However, evidence
for the FTT reaction would tend to get lost because FTT reactions create them
in much lower abundances than Strecker synthesis.
If an asteroid with an initial amino acid supply from FTT reactions was
later altered by water and Strecker synthesis, it would overwrite the small
contribution from the FTT reactions, according to the team.
The team believes the majority of the amino acids they found in the 14
meteorites were truly created in space, and not the result of contamination
from terrestrial life, for a few reasons.
First, the amino acids in life (and in contamination from industrial
products) are frequently linked together in long chains, either as proteins in
biology or polymers in industrial products. Most of the amino the amino
acids discovered in the new research were not bound up in proteins or polymers.
In addition, the most abundant amino acids found in biology are those
that are found in proteins, but such "proteinogenic" amino acids
represent only a small percentage of the amino acids found in the meteorites.
Finally, the team analyzed a sample of ice taken from underneath one of
the meteorites. This ice had only trace levels of amino acids suggesting the
meteorites are relatively pristine.
The experiments showing FTT reactions produce amino acids were
performed over 40 years ago. The products have not been analyzed with modern
techniques, so the exact distributions of amino acid products have not been
The team wants to test FTT reactions in the laboratory using a variety
of ingredients and conditions to see if any produce the types of amino acids
with the abundances they found in the 14 meteorites.
The team also wants to expand their search for amino acids to all known
groups of carbon-rich meteorites. There are eight different groups of
carbon-rich meteorites, called "carbonaceous chondrites."
The new work adds
two additional groups to the three previously known to have produced amino
acids, leaving three groups to be tested. These three remaining groups have a
high metal content as well as evidence for high temperatures.
"We'll see if they have amino acids also, and hopefully gain some
insight into how they were made," says Burton. When the team began looking for amino
acids in carbon-rich meteorites, it was considered somewhat of a long shot, but
now: "We would be surprised if we didn't discover amino acids in a
carbon-rich meteorite," says Burton.
The research was funded by the NASA Astrobiology Institute (NAI), the GoddardCenter for Astrobiology, and the NASA
Cosmochemistry Program. NAI is managed by NASA Ames Research Center in Mountain
View, Calif. Dr. Burton was supported by the NASA Postdoctoral Program,
administered by Oak Ridge Associated Universities through a contract with NASA.
Meteorite samples were provided by Dr. Kevin Righter of NASA's JohnsonSpaceCenter, Houston, Texas.