The timeline for the origins of life on Earth keeps getting pushed further back. Back when I was in school nearly four decades ago, the thought was the first life on Earth formed some three billion years ago. New studies continued to push that figure back further, and today, the generally accepted theory is the first one-celled life formed on Earth around 3.8 billion years ago.
A new study, however, is challenging the conventional assumption that the “Hadean era” of more than four billion years ago was simply too hot and inhospitable to support any kind of life.
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The study, published this fall in the Proceedings of the National Academy of Sciences (PNAS), offers proof of early life trapped in zircon crystals. A naturally occurring mineral, zircon crystals preserve materials from their environment as they form. Moreover, these tiny crystals are very tough, so they are kind of like miniature “time capsules” of sorts as most other minerals that may have incorporated contemporaneous matter break down over time.
The new study analyzed more than 10,000 zircons from the Jack Hills of Western Australia, and found a single crystal with a nugget of pure carbon in the form of graphite. This zircon was dated at 4.1 billion years old, and, most importantly, an analysis of the carbon proves it is likely, but not definitively, formed by organic processes (such as photosynthetic bacteria, for example).
More on zircon crystals suggesting first life on Earth at 4.1 billion years ago
“We know there was liquid water,” explains Mark van Zuilen, a researcher from the Paris Institute of Earth Physics. “There’s nothing that holds us back from assuming life was there.” However, van Zuilen and others say they’re not sure the new study provides compelling evidence that it was.
The study authors argue the early Earth was apparently more hospitable than thought. Other more recent studies have confirmed this, suggesting here was liquid water even as far back four billion years ago in the Hadean. The researchers also point out if simple life arose very quickly in the early days of Earth, that could mean that simple life is relatively common.
However, keep in mind it’s possible that something besides a photosynthesizing organism created this bit of carbon. While certainly a fascinating find, it is far from definite proof that life existed 4.1 billion years ago.
Statement from lead researcher Elizabeth Bell
Commenting on the graphitic carbon found included in the zircon crystal, “On Earth today, if you were looking at this carbon, you would say it was biogenic,” lead author Elizabeth Bell, a geochemist at the University of California, noted in a recent interview. “Of course, that’s more controversial for the Hadean.”
Bell went on to say that her research added to the growing amount of evidence that the very early Earth was more hospitable than scientists thought. “The traditional view of the Earth’s first few hundred million years was that this was a sterile, lifeless, hot planet that was constantly being bombarded by meteorites,” she commented. But at least partly due to the new data from Jack Hills zircons in recent years, most geo-paleologists now believe conditions on Earth during the Hadean were mild enough that life is a real possibility.