text: Evidence for carbon cycling or biologic activity can be derived from carbon isotopes, because a high 12 C/ 13 C ratio is characteristic of biogenic carbon due to the large isotopic fractionation associated with enzymatic carbon fixation. The earliest materials measured for carbon isotopes at 3.8 Ga are isotopically light, and thus potentially biogenic. Because Earth’s known rock record extends only to ∼4 Ga, earlier periods of history are accessible only through mineral grains deposited in later sediments. We report 12 C/ 13 C of graphite preserved in 4.1-Ga zircon. Its complete encasement in crack-free, undisturbed zircon demonstrates that it is not contamination from more recent geologic processes. Its 12 C-rich isotopic signature may be evidence for the origin of life on Earth by 4.1 Ga. 
   
   Abstract ||||| Oct 19 An ancient zircon crystal unearthed in Western Australia may hold evidence that life appeared on the planet 4.1 billion years ago, or about 300 million years earlier than previously thought, according to a team of U.S. researchers. 
   
   Scientists from Stanford University and the University of California, Los Angeles said they recently collected some 10,000 multibillion year-old zircons in Jack Hills, Australia, including one believed to contain a carbon deposit that is 4.1 billion years old, give or take 10 million years. 
   
   "Its complete encasement in crack-free, undisturbed zircon demonstrates that it is not contamination from more recent geologic processes ... (and) may be evidence for the origin of life on Earth by 4.1 (billion years ago)," according to a paper published by the team in the Proceedings of the National Academy of Sciences on Monday. 
   
   Scientists have used the fossil record to assert that the history of life on Earth began about 3.8 billion years ago, in the form of single-celled creatures. Humans are believed to have first appeared on Earth only about 200,000 years ago. 
   
   The study was authored by Elizabeth Bell, Patrick Boehnke, and T. Mark Harrison of the University of California, Los Angeles along with Wendy Lao of Stanford. (Reporting by Richard Valdmanis in Boston; Editing by Eric Beech) ||||| UCLA geochemists have found evidence that life likely existed on Earth at least 4.1 billion years ago — 300 million years earlier than previous research suggested. The discovery indicates that life may have begun shortly after the planet formed 4.54 billion years ago. 
   
   The research is published today in the online early edition of the journal Proceedings of the National Academy of Sciences. 
   
   “Twenty years ago, this would have been heretical; finding evidence of life 3.8 billion years ago was shocking,” said Mark Harrison, co-author of the research and a professor of geochemistry at UCLA. 
   
   Reed Hutchinson/UCLA. Mark Harrison at UCLA. 
   
   “Life on Earth may have started almost instantaneously,” added Harrison, a member of the National Academy of Sciences. “With the right ingredients, life seems to form very quickly.” 
   
   The new research suggests 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. 
   
   Scientists had long believed the Earth was dry and desolate during that time period. Harrison’s research — including a 2008 study in Nature he co-authored with Craig Manning, a professor of geology and geochemistry at UCLA, and former UCLA graduate student Michelle Hopkins — is proving otherwise. 
   
   “The early Earth certainly wasn’t a hellish, dry, boiling planet; we see absolutely no evidence for that,” Harrison said. “The planet was probably much more like it is today than previously thought.” 
   
   The researchers, led by Elizabeth Bell — a postdoctoral scholar in Harrison’s laboratory — studied more than 10,000 zircons originally formed from molten rocks, or magmas, from Western Australia. Zircons are heavy, durable minerals related to the synthetic cubic zirconium used for imitation diamonds. They capture and preserve their immediate environment, meaning they can serve as time capsules. 
   
   The scientists 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. 
   
   Bell and Boehnke, who have pioneered chemical and mineralogical tests to determine the condition of ancient zircons, were searching for carbon, the key component for life. 
   
   One of the 79 zircons contained graphite — pure carbon — in two locations. 
   
   “The first time that the graphite ever got exposed in the last 4.1 billion years is when Beth Ann and Patrick made the measurements this year,” Harrison said. 
   
   How confident are they that their zircon represents 4.1 billion-year-old graphite? 
   
   “Very confident,” Harrison said. “There is no better case of a primary inclusion in a mineral ever documented, and nobody has offered a plausible alternative explanation for graphite of non-biological origin into a zircon.” 
   
   The graphite is older than the zircon containing it, the researchers said. They know the zircon is 4.1 billion years old, based on its ratio of uranium to lead; they don’t know how much older the graphite is. 
   
   The research suggests life in the universe could be abundant, Harrison said. On Earth, simple life appears to have formed quickly, but it likely took many millions of years for very simple life to evolve the ability to photosynthesize. 
   
   The carbon contained in the zircon has a characteristic signature — a specific ratio of carbon-12 to carbon-13 — that indicates the presence of photosynthetic life. 
   
   “We need to think differently about the early Earth,” Bell said. 
   
   Wendy Mao, an associate professor of geological sciences and photon science at Stanford University, is the other co-author of the research. 
   
   The research was funded by the National Science Foundation and a Simons Collaboration on the Origin of Life Postdoctoral Fellowship granted to Bell. ||||| Did life have hellish origins? Carbon with an organic-like signature has been discovered sealed within a crystal that formed during an interval of Earth’s history named after Hades, the underworld of Greek mythology. The find predates other evidence of life by 300 million years. 
   
   Our planet formed roughly 4.5 billion years ago, but it’s anyone’s guess exactly when life first appeared. The oldest reliable fossils are about 3.43 billion years old. Chemical signatures in even older rocks suggest life might have been present 3.8 billion years ago. 
   
   All of these early fossil signatures belong to the Archaean, which began 4 billion years ago. It is generally thought that conditions on Earth before then were so extreme that life wouldn’t have stood a chance of survival – which is why the pre-Archaean stage of Earth’s history has been dubbed the Hadean. 
   
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   Signs of life 
   
   But Elizabeth Bell and Mark Harrison at the University of California, Los Angeles, and their colleagues think life might have existed in the Hadean after all. 
   
   They analysed more than 10,000 zircon crystals smaller than a millimetre in length that date from the Archaean and Hadean. In one Hadean crystal they found tiny flecks, or inclusions, of graphite, which must have been incorporated into the zircon crystal when it formed some 4.1 billion years ago. 
   
   The researchers analysed the carbon isotopes in two of the graphite flecks, and found both graphite flecks had a high carbon-12 to carbon-13 isotope ratio, a characteristic feature of organic origins as life preferentially absorbs carbon-12. 
   
   It’s not the first time that people have claimed the discovery of potentially organic carbon in Hadean zircons – but the carbon in those earlier claims turned out to be an artefact of the preparation techniques used to study the zircons, says Harrison. “I think there will be little dispute regarding the primary nature of the inclusions,” he says. 
   
   What will be up for discussion is whether the isotopic signature is evidence for the presence of life, says Bell. The general chemical make-up of the zircon crystals suggests that the magma they cooled from was generated by the melting of a mud-rich sediment, which is the sort of environment in which organic remains might accumulate. 
   
   Lifeless reactions 
   
   But the team points out there are also inorganic ways that isotopically light carbon could have accumulated in Hadean environments, for instance, through some of the Fischer-Tropsch chemical reactions that can turn carbon monoxide and hydrogen into liquid hydrocarbons. 
   
   Ultimately, carbon isotope data on its own is too ambiguous to decide whether Hadean carbon is evidence of Hadean life, says Thomas McCollom at the University of Colorado, Boulder. “I know a lot of people want to use such data as evidence of life, but this is governed more by what they want the outcome to be rather than scientific principles,” he says. 
   
   It’s always going to be tough to convince everyone to accept that Hadean zircons carry proof of life. “Proof is a realm better suited to mathematics than the natural sciences,” says Steve Mojzsis also at the University of Colorado, Boulder. 
   
   Even so, he thinks the new study is important. “Harrison and his team have challenged us now to think deeply about just how ancient the biosphere could be and to find new ways to explore for a cryptic record of it.” 
   
   Journal reference: PNAS, DOI: 10.1073/pnas.1517557112 
   
   Read more: “First life: The search for the first replicator” 
   
   Image credit: Richard Bizley/SPL 
   
   Correction: This article has been updated to clarify that it is the ratio of different carbon isotopes, not just the presence of those isotopes, that is characteristic of organic origin.
target: – Life of one kind or another has been around on this planet for 300 million years longer than thought, according to US researchers who took a close look at some incredibly ancient crystals unearthed in Australia. The scientists say that the zircon crystals from 4.1 billion years ago contain a telltale carbon deposit that appears to have come from something organic, Reuters reports. That's getting closer to the origin of the planet itself, roughly 4.5 billion years ago. Before now, the earliest hint of life was found in rocks 3.8 billion years old. There's no chance the carbon deposit could be any younger than the zircon because the crystal is crack-free and undisturbed, the researchers write in the Proceedings of the National Academy of Sciences. The zircon crystals were formed during a geological era known as the Hadean, after Hades, because conditions were thought to be so hellish that no life could have existed, the New Scientist notes. The UCLA and Stanford researchers now dispute that, saying life on Earth may have formed "almost instantaneously"—and restarted quickly if it were wiped out at some point. "The early Earth certainly wasn't a hellish, dry, boiling planet; we see absolutely no evidence for that," study co-author Mark Harrison says in a UCLA press release. "The planet was probably much more like it is today than previously thought.” (Earth's first big predator may have been an enormous sea scorpion.)