Subaru: Orion Nebula: Clues about the Origin of Life

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bystander
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Subaru: Orion Nebula: Clues about the Origin of Life

Post by bystander » Sat Jul 31, 2010 2:32 am

Images of the Orion Nebula Give Clues about the Origin of Life on Earth
Subaru Telescope | National Astronomical Observatory of Japan | 29 July 2010
How did life on Earth begin? One hypothesis is that terrestrial life began when organics were delivered from outer space during the early, heavy bombardment phase of Earth's development. We know that several meteorites (e.g., Murchison) have amino acids with properties similar to those seen in biological amino acids, the building blocks of life.

An international team of astronomers led by Fukue and Tamura of the National Astronomical Observatory of Japan conducted research on the properties of light in a massive star-forming region (BN/KL Nebula) of the Orion Nebula and have investigated a process that may have played a role in the development of life on Earth.

The origin of what is technically called "biomolecular homochirality" is a longstanding mystery and an important one to solve, since it characterizes most life forms on Earth. Chirality refers to the handedness of an image or phenomenon, which is not identical to the mirror image of its counterpart, much as the right and left hands are similar in structure but are opposites and thus not the same.

Homochirality means that a group of molecules exhibit the same handedness. Therefore, biomolecular homochirality indicates an organic group of molecules that are characterized by the same handedness. Terrestrial living material displays homochirality and consists almost exclusively of one enantiomer, L-amino acid, one of a pair of amino acids (Fig.1). What is intriguing is that amino acids in several meteorites show enantiomeric excesses of the same handedness as that seen in biological amino acids. Therefore, the process that produced the handedness of amino acids in the meteorites may provide clues to how homochirality developed in life forms on Earth. The larger question becomes how enantiomeric excesses can be produced and under what conditions.

Addressing this question became the context within which the research team worked as they made observations of the Orion Nebula, one of the brightest and closest regions of high and low mass star formation near Earth.
Extended High Circular Polarization in the Orion Massive Star Forming Region:
Implications for the Origin of Homochirality in the Solar System
-- T Fukue et al

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Re: Subaru: Orion Nebula: Clues about the Origin of Life

Post by neufer » Sat Jul 31, 2010 3:22 am

bystander wrote:Images of the Orion Nebula Give Clues about the Origin of Life on Earth
Subaru Telescope | National Astronomical Observatory of Japan | 29 July 2010
Homochirality means that a group of molecules exhibit the same handedness. Therefore, biomolecular homochirality indicates an organic group of molecules that are characterized by the same handedness. Terrestrial living material displays homochirality and consists almost exclusively of one enantiomer, L-amino acid, one of a pair of amino acids (Fig.1). What is intriguing is that amino acids in several meteorites show enantiomeric excesses of the same handedness as that seen in biological amino acids. Therefore, the process that produced the handedness of amino acids in the meteorites may provide clues to how homochirality developed in life forms on Earth.
Art Neuendorffer

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Re: Subaru: Orion Nebula: Clues about the Origin of Life

Post by Ann » Sat Jul 31, 2010 9:00 am

How did life on Earth begin? One hypothesis is that terrestrial life began when organics were delivered from outer space during the early, heavy bombardment phase of Earth's development. We know that several meteorites (e.g., Murchison) have amino acids with properties similar to those seen in biological amino acids, the building blocks of life.
Why is it that organics are hypothesized to have existed on meteorites, but not on primeval Earth?

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Re: Subaru: Orion Nebula: Clues about the Origin of Life

Post by neufer » Sat Jul 31, 2010 3:01 pm

Ann wrote:
How did life on Earth begin? One hypothesis is that terrestrial life began when organics were delivered from outer space during the early, heavy bombardment phase of Earth's development. We know that several meteorites (e.g., Murchison) have amino acids with properties similar to those seen in biological amino acids, the building blocks of life.
Why is it that organics are hypothesized to have existed on meteorites, but not on primeval Earth?
The beginnings of life in our solar system could have gotten a head start by taking place far away from a very hot and quite possibly hostile early earth. In any event, organic meteorites provide are evidence that "many organic compounds which are components of life on Earth, were already present in the early solar system and may have played a key role in life's origin."
http://news.nationalgeographic.com/news/2006/11/061130-meteorite.html wrote:
Meteorite's Organic Matter Older Than the Sun, Study Says
Brian Handwerk for National Geographic News November 30, 2006

<<Organic globules found in a meteorite that slammed into Canada's Tagish Lake may be older than our sun, a new study says. The ancient materials could offer a glimpse into the solar system's planet-building past and may even provide clues to how life on Earth first arose. "We don't really look at this research as telling us something about [the meteorite itself] as much as telling us something about the origins of the solar system," said Scott Messenger of the NASA Johnson Space Center in Houston, Texas.

Most of the meteorite's material is about the same age as our solar system—about 4.5 billion years—and was likely formed at the same time (tour a virtual solar system). But the microscopic organic globules that make up about one-tenth of one percent of the object appear to be far older. In a study appearing in tomorrow's issue of the journal Science, Messenger and colleagues report that isotopic anomalies in the globules suggest that they formed in very cold conditions—near absolute zero. "What's really striking about this is that these globules clearly could not possibly have formed where [the meteorite] itself formed," Messenger said. "Under those extreme conditions the air that you'd breathe would be solid ice. You would never find those conditions in the asteroid belt or anywhere close to the sun."
The Tagish Lake meteorite flashed across Earth's northern sky in January 2000. Most of the object burned up in the atmosphere, but pieces of it crashed in Canada's frozen, sparsely populated Yukon Territory and northern British Columbia (map of Canada).

"It's the lowest density meteorite that's ever been studied," said Peter Brown, a meteor expert and professor at the University of Western Ontario in Canada. "It's extremely friable"—easily pulverized—"and the material breaks up very easily." The object's fragile nature is one of the clues that led some scientists to theorize that Tagish Lake could be the most primitive meteorite ever discovered.

"By primitive we don't mean the oldest chronologically," explained Brown, who is not involved with the Science study. "We mean that the material in the meteorite has been processed the least since it was formed. The material we see today is arguably the most representative of the material that first went into making up the solar system." The meteorite likely formed in the outer reaches of the asteroid belt, but the organic material it contains probably had a far more distant origin. The globules could have originated in the Kuiper Belt group of icy planetary remnants orbiting beyond Neptune. Or they could have been created even farther afield. The globules appear to be similar to the kinds of icy grains found in molecular clouds—the vast, low-density regions where stars collapse and form and new solar systems are born.

Links to Life?

Some scientists speculate that organic matter arriving via ancient meteorites and comets are responsible for the rise of life on Earth. The unique shape of the newfound globules could be of particular interest to supporters of this theory. The structures are invisible to the naked eye and resemble minute hollow balls with carbon-rich shells. A chunk of meteorite no larger than a grape could contain a billion of the tiny globules. Theoretically, their hollow-ball shape could have presented a homey environment of concentrated organic matter where early cellular life could develop.

Such theories boast little evidence but raise many intriguing questions. "We don't claim that these things are alive or anywhere close to being alive," NASA's Messenger cautioned. "But the fact is that this material fell down on Earth, and similar if not identical material has been falling onto the Earth for its entire history. "Understanding the origins of that matter is inherently tied in with understanding the origins of life.">>
http://en.wikipedia.org/wiki/Murchison_meteorite wrote:
<<The Murchison meteorite is named after Murchison, Victoria, in Australia. It is one of the most studied meteorites due to its large mass (>100 kg), the fact that it was an observed fall, and it belongs to a group of meteorites rich in organic compounds.

On 28 September 1969 at about 10:58 AM, near the town of Murchison, Victoria in Australia, a bright fireball was observed to separate into three fragments before disappearing, leaving a cloud of smoke. About 30 seconds later, a tremor was heard. Many specimens were found over an area larger than 13 km², with individual masses up to 7 kg; one, weighing 680 g, broke through a roof and fell in hay. The total collected mass exceeds 100 kg.
The meteorite belongs to the CM group of carbonaceous chondrites (see meteorite classification). Like most CM chondrites, Murchison is petrologic type 2, which means that it experienced extensive alteration by water-rich fluids on its parent body before falling to Earth. CM chondrites, together with the CI group, are rich in carbon and are among the most chemically primitive meteorites in our collections. Like other CM chondrites, Murchison contains abundant CAIs. Over 100 amino acids (some of the basic components of life) have been identified in the meteorite.

Murchison contains common amino acids such as glycine, alanine and glutamic acid as well as unusual ones like isovaline and pseudoleucine. The initial report stated that the amino acids were racemic (that is, the chirality of their enantiomers are equally left- and right-handed), indicating that they are not present due to terrestrial contamination. A complex mixture of alkanes was isolated as well, similar to that found in the Miller-Urey experiment. Serine and threonine, usually considered to be earthly contaminants, were conspicuously absent in the samples. A specific family of amino acids called diamino acids was identified in the Murchison meteorite as well.

More research found that some amino acids were present in enantiomeric excess, leading some to suspect terrestrial contamination, since it would be "unusual for an abiotic stereoselective decomposition or synthesis of amino acids to occur with protein amino acids but not with non-protein amino acids." In 1997 research showed that individual amino-acid enantiomers from Murchison were enriched in the nitrogen isotope 15N relative to their terrestrial counterparts, which confirmed an extraterrestrial source for an L-enantiomer excess in the Solar System. The list of organic materials identified in the meteorite was extended to polyols by 2001.

Building on the idea that homochirality (existence of only left-handed amino acids and right-handed sugars) is triggered by deposition of chiral molecules on meteorites, research in 2005 demonstrated that an amino acid like L-proline is capable of catalyzing the formation of chiral sugars. The catalysis is non-linear, that is proline with an enantiomeric excess of 20% yields an allose with enantiomeric excess of 55% starting from a benzyloxy acetaldehyde in a sequential aldol type reaction in an organic solvent like DMF. In other words a small enantiomeric excess of left-handed amino acids may explain terrestrial life's preference for right-handed sugars.

Code: Select all

Compound class 	Concentration (ppm)
Amino acids 	         17-60
Aliphatic hydrocarbons 	>35
Aromatic hydrocarbons 	3319
Fullerenes               >100
Carboxylic acids 	     >300
Hydrocarboxylic acids 	  15
Purines and Pyrimidines   1.3
Alcohols 	               11
Sulphonic acids  	       68
Phosphonic acids 	        2
According to Engel, several lines of evidence indicate that the interior portions of well-preserved fragments from Murchison are pristine. Engel points to the array of amino acids Murchison contains and to isotope studies to bolster his position. A 2010 study by analytical chemist Philippe Schmitt-Kopplin and his colleagues using high resolution analytical tools including spectroscopy, identified 14,000 molecular compounds including 70 amino acids in a sample of the meteorite. The limited scope of the analysis by mass spectrometry undertaken by Schmitt-Kopplin's team provides for a potential 50,000 or more unique molecular compositions, with the team estimating the possibility of millions of distinct organic compounds in the meteorite.

Measured purine and pyrimidine compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of 44.5‰ and +37.7‰, respectively, indicate a non-terrestrial origin for these compounds. These results demonstrate that many organic compounds which are components of life on Earth, were already present in the early solar system and may have played a key role in life's origin.>>
Art Neuendorffer

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