Scientists say they have found evidence of life on Earth at least 4.1 billion years ago—300 million years earlier than previous research indicated. That would suggest life began shortly after the planet formed 4.54 billion years ago, and the early planet wasn’t necessarily as hellish a place as traditional books depict.
“Twenty years ago, this would have been heretical; finding evidence of life 3.8 billion years ago was shocking,” said Mark Harrison, a co-author of the research, and a geochemist at the University of California Los Angeles.
“Life on Earth may have started almost instantaneously,” added Harrison. “With the right ingredients, life seems to form very quickly.”
The research, published in the online early edition of the journal Proceedings of the National Academy of Sciences, suggests life existed before a 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 dead in that era.
“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, tough 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 analyzed 79 zircons 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 zircons contained two bits of graphite—pure carbon. That carbon must have been there ever since the zircon formed, Harrison said—that is, 4.1 billion years ago, based on its ratio of uranium to lead.
“There is no better case of a primary inclusion in a mineral ever documented,” Harrison said. “Nobody has offered a plausible alternative explanation for graphite of non-biological origin into a zircon.”
The research suggests life in the universe could be abundant, Harrison said. On Earth, simple life seems to have formed quickly, but it likely took many millions of years for it to evolve the ability to photosynthesize, or convert sunlight into energy.
The carbon contained in the zircon also has a characteristic signature that indicates the presence of photosynthetic life, the scientists said. That signature consists of a specific ratio between two forms of carbon, carbon-12 to carbon-13.
“We need to think differently about the early Earth,” Bell said.