4.1-billion-year-old crystal may hold early signs of life
Evidence that suggests there is life on Earth 4.1 billion years ago has been found. The clues lie hidden in microscopic flecks of graphite trapped inside a single large crystal of zircon. Zircons grow in magmas, often incorporating other minerals into their crystal structures of silicon, oxygen, and zirconium. Zircons are nearly indestructible. It can outlast the rocks in which they initially formed, enduring multiple cycles of erosion and deposition.
Scientists from Stanford University and the University of California found they collected some 10,000 multibillion year-old zircons in Jack Hills, Australia. One is even believed to contain a carbon deposit that is 4.1 billion years old, give or take 10 million years.
The presence of these minerals does not prove biology existed when the zircons formed, but it does provide the opportunity to look for chemical signs of life. The graphite has a low ratio of heavy to light carbon atoms called isotopes, consistent with the isotopic signature of organic matter. "On Earth today, if you were looking at this carbon, you would say it was biogenic," Elizabeth Bell, a geochemist at the University of California, Los Angeles (UCLA), and lead author of the new study says. "Of course, that's more controversial for the Hadean."
"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 October 19, 2015.
If this study is proven to be true, and life existed 4.1 billion years ago, Bell says that the new results would support growing evidence of a more hospitable early Earth than scientists once imagined. "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 says.
