Researchers have found evidence in Western Australia that Earth may be 300 million years older than we thought.
That is the conclusion from a team of geochemists at UCLA and Stanford University who found evidence that life likely existed on Earth at least 4.1 billion years ago and may have begun shortly after the planet formed 4.54 billion years ago.
“Twenty years ago, this would have been heretical; finding evidence of life 3.8 billion years ago was shocking,” said Mark Harrison, professor of geochemistry at UCLA and the co-author of the research published this week in the journal Proceedings of the National Academy of Sciences.
“Life on Earth may have started almost instantaneously,” he said in a statement. “With the right ingredients, life seems to form very quickly.”
Because Earth’s rock record only extends to 4 billion years, earlier periods of history are accessible only through mineral grains deposited in sediments, the researchers wrote.
In this case, researchers led by UCLA’s Elizabeth Bell studied more than 10,000 zircons originally formed from molten rocks, or magmas, from Western Australia. The scientists then identified 656 zircons containing dark specks that could be revealing and closely analyzed 79 of them with Raman spectroscopy, a technique that shows the molecular and chemical structure of ancient microorganisms in three dimensions.
They were searching for carbon, the key component for life. One of the 79 zircons contained graphite – pure carbon – in two locations. The carbon contained in the zircon also has a characteristic signature – a specific ratio of carbon-12 to carbon-13 – that indicates the presence of photosynthetic life.
From that, the researchers concluded that life existed prior to the massive bombardment of the inner solar system that formed the moon’s large craters 3.9 billion years ago.
“If all life on Earth died during this bombardment, which some scientists have argued, then life must have restarted quickly,” said Patrick Boehnke, a co-author of the research and a graduate student in Harrison’s laboratory.
The researchers know the zircon is 4.1 billion years old, based on its ratio of uranium to lead. They can’t say how much older the graphite is.