Meteorites baked in Earth's hydrothermal vents might have released molecules crucial to forming cell-like membranes in early life forms. So suggest tests run on pieces of a van-sized meteor that broke up over California.
The meteor made headlines in April 2012 when it was spotted as a bright fireball over the US west. By tracking its trajectory, scientists were able to figure out where fragments should have landed and quickly collect relatively fresh pieces.
Initial tests on the pieces showed that the meteorite is a carbonaceous chondrite, a class that is usually rich in amino acids and other soluble, carbon-containing compounds. Scientists have theorised that these organics – key ingredients for life – dissolved from meteorites into Earth's seas.
But it turns out that Sutter's Mill was heated by collisions with other space rocks before it fell to Earth, which changed its composition. Other work found that the meteorite fragments seem to be oddly low in organic materials.
Hardly any soluble organics were found after boiling two more of the fragments, says Sandra Pizzarello of Arizona State University in Tempe. But her team also wanted to know how the insoluble material – the hardier and often ignored stuff in the meteorite – would withstand a six-day bake in extreme heat and pressures akin to those around hydrothermal vents, possible sites for the origin of life.
"And lo and behold, this meteorite left behind something we have never seen," says Pizzarello. The unexpected riches were polyether- and ester-containing compounds. These long molecular chains, which contain carbon and oxygen, are insoluble but float in water, much like soaps or oils. They can form scaffold-like structures and may have trapped other, soluble organics within the cell-like enclosures of early life forms, she says.
Biochemistry bubbles
The long molecular chains probably formed during the extraterrestrial heating process and so would be unique to meteorites that endured lots of collisions, like Sutter's Mill, says Pizzarello. Insoluble material from samples of other meteorites did not produce polyethers and esters when subjected to the same experimental heating. But the new result hints that some meteorites may have somehow wound up in hydrothermal vents and acted as time-release capsules, slowly letting go of vital insoluble compounds on early Earth.
"We can only speculate, but you can never say never," says Pizzarello. "A meteorite that didn't seem to be much may still have had the capability to form life. It's important to think about what could have happened to the meteorite in the process of it being on Earth."
Peter Jenniskens of the SETI Institute in Mountain View, California, led the search effort and several subsequent studies of the Sutter's Mill meteorite.
"This paper describes some compounds that can create bubbles or small spaces that biochemistry can happen in, and that in itself makes the molecules interesting," he says. "I'm excited to see that this meteorite produced some really unusual compounds. It makes the variety of compounds available for the origin of life more rich."
Journal Reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1309113110
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