World’s oldest rocks, in NWT, ‘show early Earth barrage’

An example of rock from the Acasta River region of the NWT
An example of rock from the Acasta River region of the NWT. Pedroalexandrade/Wikimedia

The world’s oldest rocks, which come from a river in the Northwest Territories, are the subject of a new paper looking into the Earth’s earliest moments.

Rocks at the Acasta River, north of Wekweètì, are four billion years old – the oldest known rock formation on the planet.

The composition of the rocks is different to that of the Earth’s early crust, which prompted researchers to explore why that should be.

A study looking at how the Acasta rocks were formed was published in the journal Nature Geoscience and scientists presented their results in Boston on Tuesday.



The study concludes the high temperatures needed to create the rocks “were likely caused by a meteorite bombardment around half a billion years after the planet formed,” stated a news release summarizing its findings.

“It would have needed something special to produce the 900°C temperatures needed,” said Tim Johnson, of Perth’s Curtin University, who led the research team. “That probably means a drastic event, most likely the intense heating caused by meteorite bombardment.

“We think that these ancient … rocks would have been very common, but the passage of four billion years, and the development of plate tectonics, means that almost nothing remains.

“We believe that these rocks may be the only surviving remnants of a barrage of extraterrestial impacts which characterized the first 600 million years of Earth history.”

As a nod to the Tłı̨chǫ people, the geologists who discovered the Acasta rocks gave them the name ‘Idiwhaa,’ which the news release states is the Tłı̨chǫ word for ‘ancient.’