A team of scientists led by the University of Alberta uncovered the secret of early Earth’s crust, thanks to the oldest rock discovered in Canada’s Northwest Territories dating back at 4.02 billion years. Their findings show that Earth was mainly covered with an oceanic crust-like surface.

“It gives us important information about how the early continents formed,” says the study’s lead author Jesse Reimink. “Because it’s so far back in time, we have to grasp at every piece of evidence we can. We have very few data points with which to evaluate what was happening on Earth at this time.”

The rock was found 300 kilometers north of Yellowknife in Northwest Territories, Canada. There are only three areas in the world that contain some of the oldest rocks on Earth. Apart from this Canadian site, the only areas that other rocks older than 4 billion years can be found are Northern Quebec and Western Australia.

However, unlike the other oldest rocks unearthed by experts, the Yellowknife rock contained well-preserved grains of the mineral zircon. Apparently, the mineral contains chemical signatures and other valuable information that did not get altered by any geological events as what the rock itself has undergone.

Analysis reveal that the oldest rock is similar to the ones currently forming in modern Iceland. They also studied the rock’s chemical signatures to determine how magma intruded into the surrounding rock at the time.

It turns out that the rock contains signatures that recorded the assimilation of magma from Earth’s crust. Reimink explains that “While the magma cooled, it simultaneously heated up and melted the rock around it, and we have evidence for that.”

Still, Reimink admits that more evidence is needed to provide further understanding of the subject. The findings can be found in the October issue of the journal Nature Geoscience.