Ever misread a clock and found yourself rushing? Just like that, geologists sometimes misinterpret the ancient clocks hidden in rocks. An exciting discovery in the Pilbara region of Western Australia has brought this to light.
Researchers recently identified a meteorite impact crater that could potentially be 3.5 billion years old. If confirmed, it would be the oldest known impact site on Earth. However, a separate study suggests the crater formed later—after 2.7 billion years ago—making it much younger than initially thought. This reveals just how tricky dating geological events can be, as both studies relied on different methods and interpretations.
Planetary scientists are keen on finding ancient craters to unlock Earth’s early history. So far, the oldest recognized impact structure is the 2.23-billion-year-old Yarrabubba crater, also in Australia. The new crater, located in a barren area known as North Pole Dome, is unlike any other.
The earlier report claimed it was massive—over 100 kilometers in diameter. Our study, however, suggests it’s smaller, around 16 kilometers across. This size matters: a larger crater might have influenced continental crust formation or even early life. Our findings indicate this impact didn’t play such a significant role due to its later age and smaller size.
How can two studies reach such different conclusions? The answer lies in subtle clues left in the rock formations. Both teams found shatter cones, which are unique imprints formed by the shock of a meteorite impact. These telltale signs confirm an ancient collision but do not solve the age puzzle.
Interestingly, shatter cones are fossilized signatures of massive pressures. Both teams found them, agreeing on the crater’s impact origin but diverging on the timeline. We collaborated with local Aboriginal people, the Nyamal, to honor their heritage in naming it the “Miralga impact structure.”
To date the impact, we couldn’t rely on conventional radiometric dating, which is often used for rocks. Instead, we turned to the law of superposition, which tells us that younger rocks sit atop older ones. While the first study pinned the impact at 3.47 billion years based on older rock layers, we found shatter cones in younger layers, indicating the impact had to have occurred more recently.
Our mapping revealed numerous shatter cones within a 6-kilometer area, helping us conclude the crater’s diameter is 16 kilometers—significantly smaller than thought. This diminutive size lessens the crater’s potential impact on Earth’s geological or biological history.
While the Miralga crater may not be the oldest, it still offers valuable insights. Impact craters in basalt are rare, making Miralga a fascinating site for scientists, especially those interested in Mars exploration. The chemical alterations of these ancient basalts could mirror early conditions on Mars, making it a significant comparison for future studies on the Red Planet.
In science, new evidence often reshapes old narratives. The findings from the Miralga impact structure add depth to our understanding of Earth’s geological past and highlight the complexity inherent in studying ancient impacts.
