Earth's oldest known impact structure, the North Pole Dome in Western Australia's Pilbara region, has been precisely dated to 3.024 billion years ago, according to a new study published in Geology. The research used tiny crystals within shocked rocks to confirm the age, making it the only recognized impact crater from the Archean eon (4 to 2.5 billion years ago).
Ancient rocks preserve impact evidence
The Pilbara contains some of Earth's oldest rocks, close to 3.5 billion years old. These dark, weathered volcanic rocks include pillow basalts—lava that erupted underwater and cooled on an ancient seafloor. On some surfaces, fine lines fan through the rock, forming shatter cones: the frozen signature of a meteorite shock wave and the clearest indicator of an ancient impact.
When the team first reported these rocks in 2025, they suggested they were part of an ancient impact crater at the ironically named North Pole Dome. However, the exact age of the impact remained uncertain. The new study, led by Chris Kirkland of Curtin University, used mineral dating to pinpoint the event.
Mineral clocks solve the age puzzle
The key mineral was zircon, which contains uranium that decays into lead at a known rate. By measuring uranium and lead ratios, researchers can estimate when a crystal formed or was strongly altered. In one shatter cone, the team found skeletal zircons—tiny, lightning-bolt-shaped crystals that can form under rapid conditions like an impact. The best-preserved of these gave an age of 3 billion years.
To confirm, the team also dated apatite, a phosphate mineral that grows when hot fluids move through broken rock—exactly the kind of system an impact creates. The apatite yielded the same age: about 3.02 billion years. "Two clocks, in different minerals and different rocks, pointed to the same event," said lead author Chris Kirkland.
Challenges in dating ancient impacts
Previous estimates for the North Pole Dome impact ranged from extremely ancient to as young as 400 million years ago, based on correlation of rock layers across a complex landscape. "Linking one fine-grained black rock to another across the outback can be surprisingly hard," Kirkland explained. The new mineral dating bypasses these stratigraphic challenges by looking inside the rocks themselves.
Other minerals, such as muscovite in a vein cutting across the shatter cone, gave younger ages (about 1.66 billion years), but these reflect later geological events, not the impact itself.
Significance for Earth's early history
Earth constantly destroys its ancient surface through erosion, burial, and plate tectonics, unlike the Moon. Most craters from the early Earth have vanished. The survival of the North Pole Dome crater offers a rare glimpse into the violent youth of our planet. "Its rocks preserve the trace of a space impact from 3.024 billion years ago—a rare page from the violent youth of our planet, with the date still written in the stone," Kirkland said.
The study confirms the North Pole Dome as the oldest known impact structure on Earth, providing a critical benchmark for understanding impact rates and conditions in the Archean eon.
