Whitehouse has introduced an additional argument to challenge the assertion of a 3.95-billion-year-old date, focusing on hafnium isotopes found within the same zircon crystals.
This method leverages the radioactive decay of lutetium-176 to hafnium-176. If the age of 2.8 billion years were the result of later thermal alterations, it would have originated from materials exhibiting a hafnium isotope ratio incompatible with that of early Earth.
“They yield impossible values,” Whitehouse stated.
According to Whitehouse, the only way the uranium-lead ratio can mesh with the hafnium present in the zircons is if these zircon crystals formed from sediment about 2.8 billion years ago, thereby limiting the organic carbon to that age or younger.
The Newest Ancient Evidence of Life on Earth
If the carbon from Labrador is no longer deemed the oldest indicator of life on Earth, the inquiry becomes: where might the earliest remnants of life now lie?
Whitehouse points to the 3.77-billion-year-old Isua Greenstone Belt in Greenland as the current candidate. “I believe that this age is well-documented… it’s what I consider the strongest evidence for the oldest signs of life we possess,” Whitehouse asserted.
O’Neil, who recently co-authored a paper on Earth’s oldest surviving crustal rocks near Hudson Bay in Canada, suggests another perspective. “In my view, the evidence lies within the Nuvvuagittuq Greenstone Belt,” O’Neil remarked, citing these rocks as potentially 4.3 billion years old. “Of course, this view is not universally accepted!” Notably, these rocks are thought to contain carbon that may have a biological origin and could represent the type of underwater vents where life might have initially developed.
However, the overarching takeaway is the existence of credible traces of life that date back several billion years—whether 3.8, 3.9, or even 4.3 billion years.
Any of these dates highlight a significantly early point in Earth’s 4.6-billion-year timeline. These findings predate the formation of an oxygenated atmosphere, the emergence of continents above sea level, and the initiation of plate tectonics. Additionally, these findings are far older than the most ancient microbial “stromatolite” fossils, estimated to be around 3.48 billion years old.
O’Neil suggests that once the Earth became habitable, life may have arisen relatively swiftly: “It doesn’t surprise me because the conditions were similar,” he stated. “The Earth benefits from a long timeframe… but biology can be quite rapid. So if all favorable conditions existed by 4.3 billion years, why would life wait another 500 million years to emerge?”
