A Fragment of Earth's Original Crust Still Exists—and It's Buried in Canada
Here's what you'll learn in this story:
What are now thought to be the oldest rocks on Earth have been confirmed to have an age of almost 4.2 billion years, almost as old as the planet itself.
Researchers were met with controversy for their initial claims, but dating isotopes of one metal that decayed into another showed that the igneous rock from northeastern Canada really was that old.
This ancient piece of our planet could tell us more about its turbulent past.
Earth is about 4.5 billion years old, and as the eons passed, the crust of the young planet experienced turbulence. Asteroid collisions shattered some parts, which melted and recrystallized, while tectonic plates constantly shifted and triggered volcanic eruptions that oozed magma over the surface. Erosion further erased evidence of our planet's early scars. The most ancient layers of crust were all but lost—until now.
The oldest crust on our planet formed during what is known as the Hadean epoch. Reaching back to the period between 4.6 to 4 billion ago, this was when the Solar System was still forming in a thick haze of gas and dust (possibly the refuse from a supernova) that surrounded the nascent Sun. It is an epoch not even considered part of geologic time because, for years, the only rocks found dating back from this period were meteorites that fell from space.
Hadean meteorites and lunar rocks up to 4.5 billion years old have been found before, but nothing directly from Earth even came close. As Earth became covered in swaths of ocean, layers of soil and landscapes as diverse as forests, deserts, mountains, volcanic plains, glaciers, grasslands and cities built by humans, primordial relics were buried even deeper.
Anything found to have been part of our planet's crust in the distant past was 3.8 billion years old or younger. That puts even our latest findings in the Archean period, which followed the Hadean.
Geologist Jonathan O'Neil of Ottawa University in Canada refused to believe there were no Hadean fragments of crust remaining. While zircons found embedded in Australian rocks were successfully dated back to that period, an actual piece of crust that old had never surfaced. In a controversial 2008 study, O'Neil and his research team claimed that they had discovered a part of the original crust in northeast Canada's remote Nuvvuagittuq Greenstone Belt. This formation has stayed intact almost since Earth was born. It could be a portal into Earth's earliest growing pains.
There was just one problem. Another group of researchers steadfastly argued that the rocks of the Nuvvuagittuq Greenstone Belt were no older than 3.8 billion years. While the 4-billion-year-old rocks of the Acasta gneiss in the northwest of Canada were slightly older, having just barely formed at the end of the Hadean, they were still not old enough. O'Neil was determined to prove that the Nuvvuagittuq rock, originally a flood plain of magma that hardened into volcanic basalt, predated the other pieces of crust.
It turned out that the evidence was hiding in the rock itself, and not in the form of zircons. When they first formed, they had contained samarium, a metal which oxidizes when exposed to air. Any samarium in the rocks was long gone. However, samarium isotopes had left behind chemical signatures of their decay into isotopes of neodymium. Two different isotopes of neodymium which had come from two samarium isotopes were both dated to 4.16 billion years.
'The age agreement between both extant and extinct radiogenic systems, in rocks related through igneous fractionation, is compelling evidence for preservation of Hadean rocks in the Nuvvuagittuq Greenstone Belt, opening a rare window into Earth's earliest times,' O'Neil and his colleagues said in a study recently published in Science.
There could be more crust that ancient which has not been unearthed yet. It is even possible that some may have landed on the Moon. 4.4 billion years ago, not long after Earth formed, an extreme collision shattered part of the Earth and formed our only satellite, which has not been explored by humans since the Apollo Era. What future Artemis astronauts find once we return to the Moon might give us more insight about how our planet grew up.
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