New evidence for life on earth 4.1 billion years ago
In a report released 19 Oct 2015 (see also this New Scientist report and the original technical article), geochemists at UCLA announced evidence that life very likely existed 4.1 billion years ago, which is at least 300 million years earlier than the previous research consensus.
According to co-author Mark Harrison of UCLA, “life on Earth may have started almost instantaneously.” Indeed, 4.1 billion years ago was near the end of the massive bombardment of the inner solar system that is still evident on the moon’s surface today.
The research consisted of studying a large number (10,000) zircon crystals from Western Australia. Zircons, which are composed of a material related to the synthetic cubic zirconium used for imitation diamonds, are extremely durable and virtually impermeable, so that material trapped inside them constitutes a very reliable picture of the environment when they formed.
656 of these zircons contained dark specks that could be studied with Raman spectroscopy, which reveals the molecular and chemical structure. One of these zircons contained graphite (carbon) in two locations. These carbon dots had a ratio of carbon-12 to carbon-13 that is a characteristic signature of photosynthetic life.
Researchers are very confident that this carbon is at least 4.1 billion years old, because the zircon that contains them is that old, based on careful measurements of its uranium-to-lead ratio.
Elizabeth Bell, a postdoctoral researcher in Harrison’s UCLA lab who worked on the project, concluded “We need to think differently about the early Earth.”
Implications for Fermi’s paradox
These findings have significant implication both for biologists, who are trying to understand the origin of life on earth, and also to scientists who puzzle over “Fermi’s paradox.”
Fermi’s paradox is the conundrum, first voiced by famed Italian-American physicist Enrico Fermi to a group of colleagues in 1950, that whereas life appears to have arisen very early on earth, and whereas there are likely billions of planets in the Milky Way that are in the habitable zone around their respective stars, yet to this date we see no evidence of any other intelligent civilization.
Researchers have studied every aspect of Fermi’s paradox, and have explored and critiqued numerous possible explanations, but none of these explanations seem very convincing. One possibility is that the appearance of life on the early earth was a freakishly unlikely development.
But this latest discovery casts serous doubt on that assumption — instead, full-fledged photosynthesis appears to have been already going on here 4.1 billion years ago, very shortly after the cease of heavy bombardment that would have sterilized life. Given that life appeared so fast, this suggests that the origin of life is not freakishly unlikely, but instead is inevitable on any suitably habitable planet.
So where is everybody? Given findings like the UCLA report above, Fermi’s paradox is more puzzling than ever.