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A Piece of the Earth’s Original Crust Still Exists in Canada

Mar 17, 2017 03:05 PM EDT
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Granite
This piece of granite from Canada contains chemical traces of the Earth's first crust.
(Photo : Dave Weatherall, University of Ottawa/Eurekalert)

Humans can still find traces of the ancient Earth lingering in the modern world, if only they know where to look. Recently, a team of geologists found remnants of the Earth's original crust in rocks from the eastern shore of Hudson Bay in Canada.

According to a report from Live Science, the rocks found by the bay are granites known to be 2.7 billion years old. A team of scientists led by Jonathan O'Neil of the University of Ottawa discovered that these granites still contain chemical traces of its precurser rocks -- rocks formed 4.3 billion years ago.

With the Earth only 4.6 billion years old and the moon about 4.5 billion years old, these precurser rocks are likely to be part of the earliest Earth's crust ever formed in the planet.

"Rocks that are 3.6 [billion] to 3.8 billion years old or older, we can count them on the fingers of our hand, basically," O'Neil explained in the Live Science report. "We have a very limited amount of rock sample to understand the first billion years of Earth history."

O'neil, along with co-author Richard Carlson of the Carnegie Institution for Science, targeted the 2.7-billion-year-old granites because the pair were aware these rocks were formed by a precurser rocks that were buried and melted to be recycled into "new" rocks.

The team used a method called samarium-neodymium dating to figure out the age of the granite's parent rock. Samarium-146, a molecular variation of samarium, is now non-existent, having gone through radioactive decay in the first 500 million years of the planet. It decays into neodymium-142.

Thus, any rock that formed after the first 500 million years of Earth will have the same ratio of neomydium-142 to other neomydium isotopes. When the granite displayed a deficit in the neodymium-142 to neodymium-144 ratio, the scientists knew the parent rock had to have formed in the early years of the planet.

"I think that it's a piece of the original crust," O'Neil said in a report from Popular Mechanics. "It was cooked, but I think it's still very close to what it used to be."

It's also likely that the parent rock was basaltic oceanic crust, not dry land.

The research team published their findings in the journal Science.

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