Parts Of Earth’s Original Crust Discovered In Canada

Posted: Mar 21 2017, 2:22pm CDT | by , Updated: Mar 21 2017, 2:30pm CDT, in News | Latest Science News

 
Parts of Earth’s Original Crust Discovered in Canada
Ancient crust was found along the eastern shores of the Hudson Bay. Credit: Rick Carlson.

4.2-billion-year-old remnants of Earth's crust were recovered from rocks in northeastern Canada

Rocks from Canada’s Hudson Bay have yielded some of the earliest pieces of Earth’s crust that existed around 4.2 billion years ago. Earth itself is a bit more than 4.5 billion years old and researchers believe the new finding can provide more insight into the origin and geological evolution of our planet.

Finding remnants of Earth’s ancient crust has proven extremely difficult over the years because this crust has been either moved inside the Earth’s interior due to the action of tectonic plates or recycled to create the new one. In any case, Earth’s original crust is no longer exists to be studied directly. That makes the discovery of Earth’s original crust a monumental achievement.

The chunks of ancient crust were found embedded in the rocks of Superior Province - a region in Canada just north of the Great Lakes. These rocks are mostly made up of granite and are themselves no more than 2.7 years old but analysis of isotope ratios of samarium and neodymium collected from the rocks suggests that they contain some pieces of 4.3 billion year old basaltic crust. The analysis suggests that our 4.2 billion years old crust was reworked and mixed into the 2.7-billion-year-old rocks of the Superior Province.

Samarium-146 is a radioactive isotope that went extinct very early in Earth's history. Researchers are aware of its existence due to the study of very ancient rocks, especially meteorites and samples from Mars and the Moon.

Samarium-146 decays into neodymium-142, so any rock that formed late in the history of Earth or after its first 500 million years holds the same ratio of neodymium-142 as the other neodymium isotopes. If any rock shows variation in the relative abundance of neodymium-142 compared to other neodymium, it must have formed in the first 500 million years of Earth history or when samarium-146 was still present – more than 4 billion years ago.

The abundances of neodymium-142 in these granite rocks indicate that they came from the re-melting of much older rocks. The composition of these ancient rocks is much similar to the abundant magnesium-rich rock type known as basalt, which makes up all of the present day oceanic crust as well as most of large volcanoes.

Some of that ancient basaltic crust, which may have formed almost after Earth's formation, remained intact from Earth's surface for at least 1.5 billion years before later being re-melted into rocks that formed most of the ancient part of Canada’s northernmost Superior.

The study was published in Science Magazine.

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