A recent discovery of zircon deposits in the Jack Hills region of Western Australia proves to be the oldest known fragments of Earth, and provides ground-breaking evidence that life on Earth could have formed earlier than previously thought.
Zircons are the gold standard for accurately determining the age of surrounding rocks; due to the fact that they are plentiful in the Earth’s crust, are exceptionally resistant to chemical changes, and have a uranium content sufficient for testing.
Dr. John Valley and his team of geoscientists chose one very small fragment to test in order to determine its age. The widely accepted uranium-lead dating technique was used first; by determining how much uranium in the zircon had decayed, Valley and his team pinpointed the zircon to be around 4.4 billion years old.
Since this technique can yield false results due to the lead’s ability of movement within and outside of the mineral, a second process was used to verify accuracy. The atom-probe technique found the lead atoms had not moved significantly, confirming the age of the zircon to be 4.4 billion years old. The significance lies in the fact that Earth itself was formed only 4.5 billion years ago, from a collision that turned it into a fiery, uninhabitable mass. By pinpointing the age of the zircon material, we can conclude that the formation of Earth’s crust was also at least 4.4 billion years ago.
This finding supports the hypothesis of a ‘cool early Earth’, where temperatures were stabilized and low enough to create a hydrosphere to support microbial life. Scientists have estimated the timeframe to be 100 million years after the formation of the crust.
“The discovery that the zircon crystal, and thereby the formation of the crust, dates from 4.4 billion years ago suggests that the planet was perhaps capable of sustaining microbial life 4.3 billion years ago,” Valley said. “We have no evidence that life existed then. We have no evidence that it didn’t. But there is no reason why life could not have existed on Earth 4.3 billion years ago,” he added.