15 February 2010

Meteorite contains complex organic molecules

Cosmos Online
Previously unknown organic molecules have been discovered in a 40-year-old meteorite, suggesting the early Solar System contained a soup of highly complex organic chemistry long before life appeared.
Murchison meteorite

The Murchison meteorite contains complex organic molecules – including carbon, hydrogen, oxygen, nitrogen and sulphur. Credit: Wikimedia

SYDNEY: Previously unknown organic molecules have been discovered in a 100 kg meteorite that hit Australia in 1969, suggesting that our early Solar System contained a soup of highly complex organic chemistry long before life appeared.

In a recent study scientists analysed the Murchison meteorite, which landed in Murchison near Melbourne, Australia, in 1969.

The meteor is thought to have originated in the early days of our Solar System, perhaps even before the Sun formed around four and a half billion years ago.

Previous studies emphasised simple molecules

Murchison is one of the most studied meteorites, already recognised for the diversity of its organic chemistry – the chemistry of compounds containing carbon.

While 70% of the carbon content in the meteorite has been classified as insoluble, previous studies have identified more than 500 organic chemical structures in the soluble fraction, resembling known biomolecules.

However, analyses of the solvent extracts up until now have all been targeted to selected classes of compounds with an emphasis on amino acids as a potential source of life on Earth, according to the study published in the U.S. journal, Proceedings of the National Academy of Sciences.

Large chemical diversity

Now, for the first time, scientists have used advanced ultra-high resolution mass spectrometry to conduct a non-targeted experiment.

In previous studies, the average formula was C100H70O12N3S2, with a high degree of aromaticity in the associated compounds. In this study, researchers found an average formula of C100H155O20N3S3, showing a higher oxygen content and higher aliphaticity (hydrogen-rich compounds not containing aromatic rings).

In old studies and in this new study, only a small number of molecules contained phosphorous, the other of the six major elements involved in life.

The researchers found 14,197 distinct elemental formulas. Taking into account the limitation of the instrument used, the researchers estimate that there may actually be more than 50,000.

Each elemental formula can have a number of different physical structures, called isomers. The molecules that the researchers discovered are large, and contain a high proportion of atoms other than carbon and hydrogen, which makes the number of possible isomers huge. The researchers estimate a “realistic minimum of several thousand isomers for any given elemental composition”.

In total, they estimate that “several millions of different chemical compounds might be present … as a result of abiotic chemistry.”

“We found a chemical diversity far superior to any samples we have analysed up until now with this technology,” said lead author Philippe Schmitt-Kopplin, an analytical chemist from the German Research Centre for Environmental Health in Munich.

“We have never seen such a complex organic system before,” he said.

According to Philippe, the newly discovered compounds in the Murchison meteorite “may have contributed to the organic complexity of the early soup” that led to the development of life on Earth.

Chemical diversity greater in space?

The findings also suggest that extraterrestrial chemical diversity surpasses that found on Earth.

The meteor probably passed through primordial clouds in the early Solar System, accumulating organic molecules in a snowball affect along the way.

By tracing the sequence of organic molecules in the meteorite, researchers believe they may also be able to create a timeline for their formation and alteration since the early days of our Solar System.

Complex primordial soup

“This is a really interesting result,” said Geraint Lewis, a cosmologist from the University of Sydney in Australia.

“Older studies looked for the simple molecules that would be required for life to form, but this study did a general search for chemistry and found a lot more complex chemical elements. So the soup which was present on the Earth just after it formed was much more complex than earlier thought,” he said.

“This will probably have significant implications for our understanding of how life on Earth began.”

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