This diamond and the zircon surrounding it, as seen by an electron microscope, are both 4 billion years old.
Credit: Thorsten Geisler & Alexander Nemchin
SYDNEY: Some intriguing diamonds discovered in Western Australia suggest that life on Earth could be 700 million years older than we thought. If proved correct, the find would raise new questions about the basic conditions required for the genesis of life.
Experts led by Alexander Nemchin, a geochronologist and tectonics expert at Curtin University in Perth, have found diamonds embedded in zircon crystals containing high concentrations of carbon 12 or "light carbon," an isotope of carbon often linked with living organisms.
Carbon 12 is thought to accumulate in living organisms because the process of photosynthesis favours it over carbon 13, the other common isotope of the element.
Oldest known carbon
In the Jack Hills of WA the Curtin University team found 22 diamond and graphite grains that are likely older than 18 zircon crystals that they were found in. These zircon crystals were dated to 4.2 billion years old – just a couple of hundred million years younger than the Earth itself.
The diamonds are the oldest known sample of carbon on Earth, say the researchers who described their findings last week in the U.K. journal Nature.
Well established evidence for life on Earth dates back to at least 3.5 billion years ago in the shape of fossilised remains of simple bacterial organisms that did not require oxygen, so if the carbon 12 is linked to life it pushes back the history of life by a further 700 million years.
This find would be significant because established theory suggest that life was unable to get a foothold on the nascent Earth until after a period of intense meteorite bombardment, known as the Late Heavy Bombardment, which occurred between 3.8 and 4.1 billion years ago.
"We interpret the range of light carbon values observed in these inclusions as a unique chemical marker that opens up the possibility of biological activity during the period not long after the Earth's formation," said Nemchin.
