Meteroite May Have Seede Earth Life
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Carbon globules in meteorite may have seeded Earth life
Slices through the Tagish Lake meteorite show hollow globules of organic matter, labelled G in these electron microscope images (K Nakamura-Messenger/NASA/JSC)
Life on Earth may have started with the help of tiny hollow spheres that formed in the cold depths of space, a new study suggests. The analysis of carbon bubbles found in a meteorite shows they are not Earth contaminants and must have formed in temperatures near absolute zero.
The bubbles, called globules, were discovered in 2002 in pieces of a meteorite that had landed on the frozen surface of Tagish Lake in British Columbia, Canada, in 2000 (see Hydrocarbon bubbles discovered in meteorite).
Although the meteorite is a fragile type called a carbonaceous chondrite, many pieces of it have been remarkably well preserved because they were collected as early as a week after landing on Earth, so did not have much time to weather.
Researchers were excited to find the globules because they could have provided the raw organic chemicals needed for life as well as protective pockets to foster early organisms.
But despite the relatively pristine nature of the meteorite fragments, there was no proof that the globules were originally present in the meteorite, and were not the result of Earthly contamination.
Now, analysis of atomic isotopes shows that the globules could not have come from Earth and must have formed in very cold conditions, possibly before the Sun was born. The research was led by Keiko Nakamura-Messenger of NASA's Johnson Space Center in Houston, Texas, US.
Cold gas cloud The globules are enriched in heavy forms of hydrogen and nitrogen, called deuterium and nitrogen-15, respectively, ruling out their formation on Earth. The relative amounts of these isotopes is characteristic of formation in a very cold environment: between 10 and 20 Kelvin above absolute zero.
This means that the globules may predate our Sun, since temperatures like these would have prevailed in the cold cloud of gas from which our Sun formed and ignited. Alternatively, the globules might have formed after the Sun but while the planets were still developing.
The right temperatures would also have existed in the outer reaches of the developing solar system where the comets are thought to have formed. Intriguingly, comets are known to contain particles of organic material of roughly the same size, although the shape of these particles is not known.
Membrane-like structures Either way, the globules are extremely old, says team member Scott Messenger, also of the Johnson Space Center. "We're looking at the original structures of organic objects that formed long before the Earth formed," he told New Scientist.
Nakamura-Messenger's team says the globules could have been important for the origin of life by providing the raw materials and membrane-like structures needed. Some scientists think that the presence of some sort of container that could separate an organism's internal chemistry from its environment was a crucial stage in the evolution of life.
"It's sort of reminiscent of membrane type structures," agrees Larry Nittler, at the Carnegie Institution of Washington in Washington DC, US. But as for whether the structures could have kick-started life on Earth, "I think thats highly speculative at this point," he says.
Journal reference: Science (vol 314, p 1439)
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