The technique allowed the researchers to determine with nanometer precision where the various building blocks of life were distributed within the Isua Greenstone Belt. These included carbon, oxygen, nitrogen, and a form of phosphate. They were lacking one important building block, however: hydrogen.
The researchers later determined that hydrogen is so small — it is the lightest chemical element — that it must have seeped through the rocks. Its absence actually provides evidence that the samples were not contaminated by more recent biological material.
What they did find, by way of the other elements, were “remains of early life trapped inside inclusions inside garnet crystals that grew in a sedimentary rock, and included parts of the sediment as inclusions,” Rosing said. “The materials inside the inclusions were part of the sediment, which formed more than 3.7 billion years ago.”
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That age has previously been confirmed by a barrage of dating methods, with measurements of the decay of uranium-to-lead providing the most definitive, precise information.
The researchers believe that the identified life-associated chemical elements within the rock are the remains of single-celled organisms, possibly bacteria. These elements are “still tightly bound to each other within the scale of single-celled organisms inside the garnets,” Rosing said.
Earlier studies speculated that remains of early life could be found in the Isua Greenstone Belt. The new research not only confirms such prior speculations, but also pinpoints what these remains consist of with greater clarity.