The potentially 4.3-billion-year-old rock that is believed to be a part of Earth’s original crust was just discovered in Canada.
By William Herkewitz
Around 4.3 billion years ago, a planetary blob of hot molten rock named Earth cooled just enough to start forming a crust. Billions of years later, humans evolved. And now, two of those humans have discovered that a chunk of that original crust is actually still around on the surface today.
A duo of geologists led by Jonathan O’Neil at the University of Ottawa have just announced the discovery of an ancient chunk of Earth’s original crust. It was found near the eastern shore of the Hudson Bay in Northwestern Quebec, in Canada. The rock is a basalt, which O’Neil’s team believes was, at one point, underneath the Earth’s first oceans. It is surrounded by a cocoon of granite rock that O’Neil and his fellow researcher, Richard Carlson of the Carnegie Institute for Science in Washington D.C., say is also just one geological step away from Earth’s original crust. The geologic findings were published today in the journal Science.
“I think that it’s a piece of the original crust. It was cooked, but I think it’s still very close to what it used to be,” O’Neil tells Popular Mechanics.
This fascinating research is based on a “scientific technique that’s relatively new, only about 10 years old,” says O’Neil. Only a handful of geology labs across the globe are using it.
The technique is basically a method of aging rocks by tracking the decay of an isotope called samarium-146. This isotope is interesting because it existed on Earth only for a short period of time after the planet formed—up until around 4 billion years ago. By then all of Earth’s samarium-146 had decayed into another isotope of the element neodymium, and it’s now functionally extinct on our planet.
By studying the ratio of different flavors of neodymium in a given rock, you can gauge how far removed that rock is from rocks that formed during Earth’s early cooling. Newer rocks that have melted and reformed a dozen times since the dawn of Earth will have a slightly different ratio of neodymium isotopes.
Near the shores of the Hudson Bay way up in Canada, O’Neil’s team analyzed a collection of granite rocks that we know (through other dating methods) are only 2.7 billion years old. Now, granite cannot have be part of Earth’s original crust because you have to form granite by melting and reforming other rocks. But the samarium-146 decay of the granite they discovered strongly suggests it is only one step removed from Earth’s original crust. What we the researchers think happened, O’Neil says, is that after 1.3 billion years of existing on the surface, part of Earth’s original crust was forced underground, where the intense heat and pressure forged it into the granite we see today.
The Original Crust
This discovery alone would be an impressive find. If you know a sample of rock is only one step removed from Earth’s first crust, terra primum, then “by studying the makeup of these rocks, you almost piece together the DNA, so to speak, of these old continents,” says O’Neil.
But alongside these firstborn granite rocks, O’Neil’s team also found a basalt that they believe actually is the original crust—which somehow survived its multi-billion-year trip underground relatively unscathed. It’s a basalt rock, and it perfectly “fits the composition of the precursor rock we believe formed everything around it,” he says. That is, the ratio of neodymium isotopes exactly fits what the geologists would expect to find in Earth’s original crust.
Don Francis, a geologist at McGill University who was not involved in the research, agrees that the find really does look likely to be part of Earth’s original crust. “It may indeed represent very early [4.3 billion year old] basaltic crust,” he says.
That’s music to O’Neil’s ears. “Its an original piece is basaltic crust, I’m convinced it is,” he says.
This article was originally written for and published by Popular Mechanics USA.