A collaboration of French and Italian researchers have discovered the first evidence of extraterrestrial carbon in Earth’s own rocks. The samples come from rocks located in modern-day South Africa that formed 3.3 billion years ago.
As reported in Geochimica et Cosmochimica Acta, the team used a technique known as electron paramagnetic resonance to study the chemical composition of the sediment. In one sample, they found two layers of insoluble organic matter. One layer was similar in composition to many other samples collected from rocks around the world, meaning its origin is certainly terrestrial. However, the same could not be said for the other sample.
The composition of the second layer doesn’t resemble any earthly rock, but it does match well with the hydrogen-rich organic material often found in carbonaceous chondrites, a specific class of meteorites. The layer is only 2 millimeters thick, possibly formed in the aftermath of one or potentially multiple impacts. Researchers have also discovered ferrite spinel nanoparticles enriched with nickel and chromium – minerals commonly formed when meteorites enter the atmosphere.
Earth was very different 3.3 billion years ago. Microbes had existed for only a few hundred million years and the atmosphere was still lacking the layer of oxygen that exists today. The researchers suggest that when the ancient meteor came down to our planet, it threw into the air a carbon-based material that settled into a layer before getting covered in volcanic ash. If so, it's possible this sample is just one of many.
“The organic matter from the carbon-rich meteorites must have been raining down at quite a high rate,” senior author Frances Westall of the CNRS Centre for Molecular Biophysics in Orléans, France, told New Scientist.
Similar layers may be hiding elsewhere in the world, but finding them is not easy. Not only do rocks change over time, but organic material, even from meteorites, may get incorporated into the carbon cycle taken in by living organisms.
The findings could also make it difficult to find simple signatures of life elsewhere in the solar system, especially Mars. Organics produced by local living organisms might be mixed with organics created in space, requiring sophisticated techniques to distinguish between the two.
[H/T: New Scientist]