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About 4.03 billion years agoReputable sourceWell documented

The oldest intact rock on Earth: the Acasta Gneiss

On the timeline · around About 4.03 billion years ago · Toward the First RocksThe Hadean EarthToward the First RocksThe oldest intact rock on Earth: the Acasta Gneiss4.2 Ga4.1 Ga4.1 Ga4.1 Ga4.1 Ga4 Ga4 Ga4 Ga

What happened

The zircons are single crystals, but the oldest whole rock still in place is the Acasta Gneiss, exposed along the Acasta River in Canada's Northwest Territories. Uranium-lead dating of zircons inside it gives an age of about 4.03 billion years, which the Geological Survey of Canada records as the oldest known rock on Earth. It began as igneous rock and was later cooked and squeezed into the banded gneiss seen today, part of the ancient core of the North American continent.

Why it matters

The Acasta Gneiss is where Earth's crust stops being a story told only by loose crystals and becomes rock we can hold and map. It is the oldest surviving piece of a continent, the start of the continuous geological record.

How we know

As with the Jack Hills grains, the age comes from uranium-lead dating of zircons, which lock in the date they crystallized and resist later disturbance. The rock's place in the Slave craton ties it to the oldest stable block of continental crust in North America.

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Part of a timelineThe Formation of the Solar System11 events · The 800 million years that turned a collapsing cloud of gas into the Sun, the planets, and a habitable Earth, from the oldest solids we can date to the first oceans.View all →