The northeastern Canadian province of Quebec is home to the oldest known rocks on Earth and likely the last remnants of our planet’s early crust.
A new study has dated the rocks to at least 4.16 billion years ago (bya) during Earth’s first geologic eon – the Hadean. The Earth is about 4.54 billion years old, placing them within the first 500 million years of the planet’s history.
The findings are presented in the journal Science.
“Earth has a habit of renewing its crust through melting and recrystallisation, thus erasing much of its early history,” Editor of Science, Angela Hessler, writes in a summary of the research.
“There are mineral fragments from the oldest eon, the Hadean, but there is little consensus on whether any intact, primordial crust still exists.”
Samples of the exceptionally old rocks were collected in 2017 from the Nuvvuagittuq Greenstone Belt (NGB) – an area of about 10 km2 near the municipality of Inukjuak, Nunavik.
“For over 15 years, the scientific community has debated the age of volcanic rocks from northern Quebec,” says Jonathan O’Neil, an associate professor in the Department of Earth and Environmental Sciences at the University of Ottawa and co-author of the paper.
“Our previous research suggested that they could date back 4.3 billion years, but this wasn’t the consensus.”
Radiometric dating is used to determine the age of a material based on the presence of radioactive isotopes within it. New analysis of the elements samarium and neodymium within the samples reveals that rocks which “intruded” into the NGB first crystallised 4.16 bya.
This means the surrounding volcanic rocks must be even older.
“This confirmation positions the Nuvvuagittuq Belt as the only place on Earth where we find rocks formed during the Hadean eon,” says O’Neil.
“Understanding these rocks is going back to the very origins of our planet. This allows us to better understand how the first continents were formed and to reconstruct the environment from which life could have emerged.”