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Living organisms may have existed on Earth as long as 4.1bn years ago – 300m years earlier than was previously thought, new research has shown.
If confirmed, the discovery means life emerged a remarkably short time after the Earth was formed from a primordial disc of dust and gas surrounding the sun 4.6bn years ago.
Researchers discovered the evidence in specks of graphite trapped within immensely old zircon crystals from Jack Hills, Western Australia.
Atoms in the graphite, a crystalline form of carbon, bore the hallmark of biological origin. They were enriched with 12C, a "light" carbon isotope, or atomic strain, normally associated with living things.
It suggests that a terrestrial biosphere had emerged on Earth as early as 4.1bn years ago, said the scientists writing in the journal Proceedings of the National Academy of Sciences.
(Score: 3, Informative) by RedBear on Friday October 23 2015, @07:43PM
Isn't the only way to date things older than a few hundred years to look at ratios of unstable isotopes vs. stable isotopes, or ratios of elements with known half-lives vs. their decay products? Perhaps that's even restating the same thing using different words. Carbon-14 has a relatively short half-life and can only be used to date things up to about 60,000 years old. But many other isotopes have known half-lives in the millions or billions of years, and looking at how much of a radioactive element present in a sample has already decayed into its known decay products can provide relatively accurate readings of how old something is, within the bounds determined by each isotope's half-life.
There may be other methods I'm not familiar with.
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(Score: 2) by frojack on Friday October 23 2015, @08:02PM
True, but that assumes no remelt occurred over the interval.
One out of 10,000 seems pretty suspect to me. I'd be looking for later inclusion events, perhaps associated with eruptions or impacts.
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(Score: 2) by HiThere on Saturday October 24 2015, @12:07AM
I think that zircons are pretty resistant to remelts. Not that they couldn't if they went into a subduction zone, but then it's hardly the same stone afterwards.
OTOH, I believe that zircons are generally dated by the rocks that they are embedded within, so if you want to argue that the stone is older than they think, that would be reasonable.
IOW, they think the stone is 4.1 billion years old, but it could be older.
FWIW, I tend to believe in Panspermia, so older wouldn't bother me. In fact older than 5 billion years wouldn't bother me, as I believe that proto-life evolved out in space. Nothing so sophisticated as a virus, however, but sharing some characteristics in common. (No cell wall, depending on the environment to build the energetic molecules that it depends on, often crystaline in form, etc.)
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(Score: 3, Informative) by Anonymous Coward on Friday October 23 2015, @10:57PM
-- https://en.wikipedia.org/wiki/Zircon#Radiometric_dating [wikipedia.org]