Scientists in Australia have discovered the world's oldest known meteorite impact crater, a 3-billion-year-old structure in Western Australia's remote Pilbara region. The finding, published in the journal Geology, provides a 'smoking gun' for an ancient collision that occurred during the Archean eon, when Earth was a water world with early life forms like stromatolites.
Research methodology and key findings
Researchers from Curtin University used two innovative dating techniques to pinpoint the age of the North Pole Dome crater. First, they analyzed tiny zircon crystals that recrystallized into skeletal patterns under the intense heat of the impact, using the Sensitive High-Resolution Ion MicroProbe (SHRIMP) to date them to approximately 3 billion years ago. Second, they dated apatite minerals that grew in fractures after the impact, yielding a similar age.
Prof Chris Kirkland, lead author and geologist from Curtin's Timescales of Minerals Systems Group, said the well-preserved rock formations offer 'a rare glimpse of the violent processes that shaped the early Earth.' He noted that such deep time capsules are extremely rare globally.
Significance and comparison to other craters
The North Pole Dome crater is now recognized as the oldest known impact structure on Earth, surpassing the Yarrabubba crater in Western Australia, previously dated at 2.2 billion years old. The discovery highlights the violent history of the early Earth, which was continuously pummeled by meteorites during the Archean eon, as evidenced by craters on the moon.
Associate professor Bruce Schaefer, a geochemist at Macquarie University not involved in the study, described the research as 'a real detective story.' He emphasized that the simultaneous resetting of zircon and apatite provides powerful evidence for the impact age, calling the combination 'the smoking gun.'
Broader implications
The findings offer insights into Earth's formative processes and the conditions that existed when tectonic plates were beginning to form. According to Kirkland, the sun was dimmer, the moon closer, and early life existed as stromatolites. The impact may have also triggered global environmental changes, such as a thaw.
Schaefer added that finding evidence of these ancient impacts on Earth is exciting because most have been erased by erosion, subduction, and plate tectonics. 'To actually see it, and put your hands on it, is very significant,' he said.
