Chiral molecules found on Murchison meteorite

By JAEMIE BENNETT | September 6, 2018

As the only known planet with life, it makes sense to assume that life began on Earth. Numerous experiments have recreated the environment of the early Earth and determined that biological molecules could have first formed on our planet.

The Miller-Urey experiment showed that organic compounds can be formed from matter in Earth’s early atmosphere by electrical stimuli, such as lightning. 

Alexander Graham Cairns-Smith further hypothesized that organic molecules first met in a clay matrix, giving the molecules the support and organization to create complex organic molecules. 

Later on, the deep-sea vent theory suggested that life began deep in the ocean, where the heat from underwater vents met the molecule-rich floor sediment to create biotic material.

But what if that wasn’t the case? 

Scientists have begun to look at space as the first home for life, especially at meteorites, which have the unique capability to transfer molecules between galaxies.

Previous work into organic material in space has proven plentiful. Amino acids and organic molecules have been discovered throughout all corners of space. This organic matter has been found as far away as the center of the Milky Way and as close as our planetary neighbor Mars.

One particular space object, the Murchison meteorite, has been a valuable specimen to scientists. 

The meteorite, which fell in 1969 in Australia, is classified as a carbonaceous chondrite meteorite. Its chemical makeup suggests that it was formed within the early solar system, when dust clouds were forming into small asteroids, and that it was never heated past its melting point. 

Over 70 different amino acids, as well as 14,000 molecular compounds, have been identified on the Murchison meteorite. 

At over 100 kilograms, the organic-compound-rich meteorite is still being used today to understand space and organic material.

Sandra Pizzarello, a former professor in the School of Molecular Sciences at Arizona State University (ASU), and Christopher Yarnes, an assistant research engineer from the University of California, Davis (UCD), recently studied extracts from the Murchison asteroid.

Pizzarello’s research includes the study of organic matter in carbonaceous chondrite meteorites, with a focus on the molecular, isotopic and chiral characterization of compounds within the meteorites. 

More recently her work has also focused on mimicking the prebiotic catalytic activity and reactions of these compounds.

Yarnes’ research focuses on compound-specific stable isotope analysis.

Pizzarello and Yarnes tested the meteorite for propylene oxide, an organic molecule that was previously found in Sagittarius B2, a dust cloud near the center of the Milky Way.

The initial finding of propylene oxide in Sagittarius B2 was important, since it is one of the most complex molecules found in space and the first to exhibit chirality. At the time, it was a huge leap in scientific understanding with regard to the synthesis of complex molecules in space.

Chirality refers to the one-handedness of a molecule: If you flip a chiral molecule over, it won’t look the same, just like a hand. Instead, it will look like the mirror image of the initial molecule.

All life on Earth exhibits a left-handed chirality, and scientists still aren’t sure why. It may simplify reactions between molecules or be because left-handed molecules were in more abundance at the time of life’s origins, but it may also be because organic molecules originated in space.

The Murchison meteorite was proven to contain the chiral propylene oxide, further confirming the possibility that biotic material originated in space and not on Earth. 

An interesting result was that polymeric compounds formed in the meteorite after being refrigerated for four weeks, which is evidence that propylene oxide could withstand the harsh environment of space travel.

Pizzarello and Yarnes suggest that there is still a lot of work to be done involving meteorites and organic compounds. 

Clearly meteorites have the capability to transport organic matter, but to what extent did that affect the origins of life on Earth?

Another yet unanswered question is whether chemical or biological reactions created biotic materials, as well as whether the chirality of organic material is caused by physical or chemical laws.

The answer to this, as well as further understanding of chirality in molecules found in space, could potentially answer the question of where life truly began: Earth, space or both?

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