Researchers have found traces of Earth's crust in the Canadian Shield dating back 4.2 billion years, when our planet was in its infancy.

Earth's composition is unlike any other known planet or moon, with rocky crusts forming and moving over the surface. Over time, this has forced older evidence of such crusts — both oceanic and continental — deep below the surface.

The oldest crust that exists today is about 2.7 billion years old, and remnants have long been known to be in the Canadian Shield.

But older crust, to roughly 4.6 billion years ago when the Earth formed, has remained elusive.

Hoping to find evidence of that original crust, Jonathan O'Neil, assistant professor at the University of Ottawa's Department of Earth and Environmental Sciences, and his team of researchers made the trip to a portion of the Shield in northern Quebec to collect samples.

Rock lineage

Rocks have a parentage but that parentage remains hidden. And trying to uncover how they first formed, and what they were compsed of, is an onerous task.

"Most granite, we believe, comes from the melting of an older crust," said O'Neil, the lead author in the resulting study, published Thursday in the journal Science.

"We knew that these rocks had an older precursor or an older parent. But how old, we didn't know."

Rocks are notoriously difficult to date. But one way to do it is by measuring an isotope that was only produced within the Earth's first 500 million years, neodymium-142; which the team found in the Quebec samples.

Close-up of 2.7 billion-year-old continental crust from Nunavik, northern Quebec showing a complex history of re-melting of oceanic-type rocks that were older than 4.2 billion years. (Véronique Villeneuve)

That means that the samples formed between 4.2 billion and 4.3 billion years ago.

Though the findings don't answer every question about Earth's early history, they do shed some light on its development.

"At least it gives us more tools to understand the early geodynamics," O'Neil said. "Was [the process] the same everywhere on Earth? Or was it local? These are all questions we'll have to answer."

O'Neil now hopes that more of these ancient cratons around the world will be studied leading to a better understanding not just about our world, but others.

"If we understand early processes that shape our planet, we can maybe understand other planets: Why are they different? Or are they similar and where in their life they drift apart in terms of geology?"