Space & Innovation

Earth’s Oldest Rocks Were Likely Formed in the Crucible of a Meteorite Impact

The 4-billion-year-old rocks of Canada’s Acasta River were formed in temperatures much hotter than Earth’s core.

This Acasta gneiss is a sample of the oldest known rock in the world. It was found in northwest Canada and is approximately 4 billion years old, just 500 million years younger than the estimated age of the Earth. | SSPL/Getty Images
This Acasta gneiss is a sample of the oldest known rock in the world. It was found in northwest Canada and is approximately 4 billion years old, just 500 million years younger than the estimated age of the Earth. | SSPL/Getty Images

The oldest rocks on Earth were likely formed by meteorites — the space rocks that occasionally survive the extraordinary heat and force of traveling through our planet’s atmosphere.

Researchers studied the roughly 4-billion-year-old silica-rich rocks of the Acasta River, which lies in Canada’s remote Northwest Territory, and found that they were formed at very high temperatures — an indication, they say, that the rocks were formed by a meteorite impact.

The rocks formed at a temperature of roughly 800 to 900 degrees Celsius (1,470 to 1,650 degrees Fahrenheit), which is much higher than temperatures in Earth’s mantle.

The research was published in the journal Nature Geoscience.

“To get rocks this hot at such shallow levels can only really be explained by meteorite impacts,” principal author Tim Johnson, a geologist at Curtin University in Australia, told Seeker.

When a space rock crashes into Earth, it creates shock waves. At the impact site, there is so much energy from the impact, it vaporizes anything nearby due to high pressures and temperatures. Rocks that are further away melt only partially, while those closer to the impact are pulverized.

"The precise scale of the effects is mainly a function of the size of the impactor," Johnson said.

"Our modeling," he added, "suggests that the [rocks] were the result of partial melting, and that the impactor must have been at least several kilometers across, but potentially much larger."

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Impacts, of course, aren't unique to Earth, so perhaps there are rocks on other worlds that also were formed by meteorite impacts. Possible locations could include Mars, Venus, and Mercury, Johnson said.

While we have pictures of these planets’ craters, a surface mission is necessary, according to Johnson to really see what the composition of the underlying rocks.

"I suspect it won't be me doing that study," Johnson joked, as surface missions often take years or decades to plan — and humans, of course, haven't ventured out past low Earth orbit since the early 1970s.