Scientists found isotopic evidence of the ‘parent rocks’ of 2.7 billion-year-old samples from the Canadian Shield, suggesting Earth’s oldest crust survived the formation of this continental feature.
In a new study, researchers from the University of Ottawa and Carnegie Science analyzed the isotope ratios of samarium and neodymium rocks from the Superior Province, which sits just north of the Great Lakes.
These samples are composed primarily of a type of granite that’s 2.7 billion years old, and formed through the ‘recycling’ of older, magnesium-rich rocks.
‘This area of northern Quebec is the nucleus of the Canadian shield,’ explained Professor Jonathan O’Neil, of the university’s Department of Earth and Environmental Sciences.
‘Previous work had shown that if we had a flavour of something older, of this ancestor, it would be there.’
Earth’s first crust has largely been driven back into the interior through geologic activity, making it difficult to pinpoint its nature.
But, using these specific isotopes, the researchers were able to study ‘the earliest time of the Earth.’
This, in turn, revealed the signature of the precursor rock.
Samarium-146 has a half-life of just 103 million years, which is short on a geological time scale.
And, while it existed at the time of Earth’s formation, it became extinct early on.
The researchers determined that the samples contained reworked crust from more than 4.2 billion years ago.
‘Now we can better understand how these nucleus of continents tabulated in time,’ O’Neil explained.
‘There’s a complex history of crustal recycling and re-melting, so the rocks are always constantly recycling and re-melting that way – and erasing lot of information about their earliest life, or where they’re coming from.’
'Whether this result implies that plate tectonics was not at work during the earliest part of Earth history can now be investigated using our tool of studying neodymium-142 variation to track the role of truly ancient crust in building up younger, but still old, sections of Earth’s continental crust,' said Carnegie’s Richard Carlson.
According to O’Neil, the results allow scientists to better pinpoint the age of the parent rock.
‘It has to be older than 4.2 billion years old, almost as old as 4.3 billion years old,’ O’Neil said.
‘So, we can piece the puzzle together to try to understand how the first continents, and the nucleus of our oldest continents were formed.’
According to dailymail.co.uk