Scientists have uncovered definitive evidence of the world's oldest known meteorite strike, a three-billion-year-old impact preserved in ancient rocks in Western Australia's Pilbara region. The discovery, made by researchers at Curtin University, confirms a cataclysmic event that occurred during the Archean eon, a pivotal time when tectonic plates were beginning to form and early life was emerging.
Rare Geological Features Confirm Impact
The findings, published in the journal Geology, focus on an area known as the North Pole Dome crater. Researchers analyzed rare geological features called shatter cones, which are distinctive fracture patterns formed only under the extreme pressure of a meteorite impact. These well-preserved formations offer what lead author Prof Chris Kirkland describes as “a rare glimpse of the violent processes that shaped the early Earth.”
“There’s very few places that are these deep time capsules that let us peer into the formative processes on our planet. That’s why they’re quite special,” said Kirkland, a geologist from Curtin’s Timescales of Minerals Systems Group.
Dating the Crater: Two Independent Methods
The researchers employed two separate dating techniques to pinpoint the age of the impact. First, they analyzed tiny zircon grains embedded in basalt rock. These grains were recrystallized by the intense heat of the meteorite strike, forming unusual skeletal patterns typically found only in impact craters on the moon. Using an Australian-designed instrument called the Sensitive High-Resolution Ion MicroProbe, the team determined that the shock event occurred approximately three billion years ago.
Separately, the scientists examined apatite, a calcium phosphate mineral that grew in rock fractures created by heat and hot fluids after the impact. The age of the apatite yielded similar conclusions, reinforcing the timeline.
Implications for Understanding Early Earth
At the time of the impact, Earth was vastly different from today. Kirkland described it as mostly a “water world” with few pieces of continental crust. The sun was dimmer, the moon closer, and early life existed in the form of stromatolites, a type of cyanobacteria similar to algae.
Associate professor Bruce Schaefer, a geochemist at Macquarie University who was not involved in the paper, said the combination of zircon and apatite dating provided a powerful “smoking gun.” “The fact those two were reset at the same time is the really powerful evidence that this is the age of that event,” he said. “The apatite and the zircon together is what’s, if you like, the smoking gun.”
Significance in the Context of Earth's History
The North Pole Dome crater now surpasses the Yarrabubba crater, also in Western Australia, which was previously considered the oldest at 2.2 billion years old. During the Archean eon, Earth was continuously “pummelled” by meteorites, Schaefer noted, with impacts still visible on the moon’s surface but largely erased on Earth by erosion, subduction, and plate tectonics.
“To be able to find evidence of those same impact events on Earth is really exciting. We know it must have happened, but to actually see it, and put your hands on it, is very significant,” Schaefer said.
