Two geologists studying North America’s oldest rocks have uncovered ancient minerals that are remnants of the Earth’s original crust which first formed more than 4.2 billion years ago.

These rocks appear to preserve the signature of an early Earth that presumably took shape within the first few hundred million years of Earth’s history.

Jonathan O’Neil and Richard Carlson uncovered the samples on a trek to the northeastern part of Canada to study the Canadian Shield formation, a large area of exposed continental crust underlying, centered on Hudson Bay, which was already known to contain some of the oldest parts of North America. O’Neil calls it the core or nucleus of the North American continent. “That spot on the shore of Hudson Bay has this older flavor to it, this older chemical signature.”

To O’Neil, an assistant professor of geology at the University of Ottawa, rocks are like books that allow geologists to study their compositions and to learn about the conditions in which they form. But as far as rock records go, the first billion years of the Earth’s history is almost completely unrepresented.

“We’re missing basically all the crust that was present about 4.4 billion years ago. The question we’re after with our study is: what happened to it?” said Carlson, director of the Carnegie Institution of Washington. “Part of the goal of this was simply to see how much crust was present before and see what that material was.”