John P. Millis, Ph.D. for redOrbit.com – Your Universe Online
Dating the formation of the Earth is a difficult process, because usually geological dating methods do not work as well. Early in its existence the Earth was more fluid, with materials all mixing together in a super-heated mix. It took millions of years for differentiation and cooling to achieve the layered Earth we live on today.
So traditional geological dating gives us more of a lower bound for the age of the Earth, while using radio-dating of solar system rocks yields an upper-limit. This is why we usually quote the Earth’s age as “less than 4.568 billion years old”. Our best estimate previously was that the Earth formed about 100 million years less than that – about 4.468 billion years – based on the geologic data and estimates for how long the formation process took.
However, geochemists Guillaume Avice and Bernard Marty from University of Lorraine in Nancy, France, have found the Earth may be even older.
According to Avice, “It is not possible to give an exact date for the formation of the Earth. What this work does is to show that the Earth is older than we thought, by around 60 [million years],” with an error of about 20 million years.
Their conclusions came by studying xenon gas found in South African and Australian quartz, which had been dated to 3.4 and 2.7 billion years respectively. By comparing the relative isotopic concentrations with those of today, the team could refine estimates of when the Earth began to form.
As Avice explains, “The composition of the gases we are looking at changes according the conditions they are found in, which of course depend on the major events in Earth’s history. The gas sealed in these quartz samples has been handed down to us in a sort of ‘time capsule’. We are using standard methods to compute the age of the Earth, but having access to these ancient samples gives us new data, and allows us to refine the measurement. The xenon gas signals allow us to calculate when the atmosphere was being formed, which was probably at the time the Earth collided with a planet-sized body, leading to the formation of the Moon. Our results mean that both the Earth and the Moon are older than we had thought”.
Of course, refining the estimate of Earth’s formation from 4.468 billion years to 4.408 billion years may not seem significant, but there are implications in various areas of planetary formation theory.
“This might seem a small difference, but it is important. These differences set time boundaries on how the planets evolved, especially through the major collisions in deep time which shaped the solar system,” added Marty.
Results of this research were presented on June 10 at the Goldschmidt Geochemistry Conference in Sacramento, California.
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