Australia’s Giant Crater: Unveiling the Oldest Impact Structure on Earth

The Arctic Dome Crater, located in Western Australia, is believed to have formed from an asteroid impact approximately 3 billion years ago. This makes it the oldest known impact crater on Earth, although its age is currently under scrutiny by some researchers.

First identified by Chris Kirkland of Curtin University in Perth, studies suggest that the crater may reach up to 100 kilometers in diameter. Kirkland’s team discovered a layer of rock featuring unique cone-shaped structures known as shatter cones, which are indicative of high-energy impacts.

While their initial research did not provide a direct age, they correlated the rock with other dated layers, estimating the age to be around 3.47 billion years. This estimation makes it significantly older than Yarrababa Crater, which is also an asteroid impact site.

This crater represents a rare occurrence from the Archean Era, when Earth’s surface was largely submerged beneath water.

However, another team, led by Aaron Cavosie, disputes the 3.47 billion-year age, asserting that the impact occurred 2.77 billion years ago. Kirkland and his researchers contend that they have now successfully dated minerals at the site, including detrital cones. Intrigued by the crater’s formation, Kirkland stated, “We’ve analyzed the rock to find minerals that directly respond to the impact’s force.”

Utilizing uranium decay rates, the researchers dated zircon found within the shatter cones and also examined apatite, believed to have formed in the heated conditions post-impact. Both minerals yielded an age of approximately 3.02 billion years, providing compelling evidence of hydrothermal activity linked to the impact.

Kirkland emphasizes that other geological processes, such as mountain-building or localized metamorphism, cannot easily account for the observed mineralogical changes in the shocked rocks. “The only plausible explanation for these changes is a shock event,” he states. “This provides strong evidence for an impact 3 billion years ago, solidifying its status as the oldest impact crater on Earth.”

While Kavosie appreciates the revised age estimates, he still believes that Kirkland’s group may be overstating the age of the crater. “We are relieved that the ‘3.5 billion year impact’ hypothesis has been withdrawn; however, we are not convinced by the arguments for an impact occurring 3.02 billion years ago,” he notes. “Science is a slow journey toward the truth.”

Kavosie pointed out that younger rocks, which are dated at 2.77 billion years, also exhibit shatter cones, indicating that any impact must have occurred after this date. Alec Brenner, a Yale University professor who criticized the original study, agrees that the rocks are the most likely younger than 2.77 billion years.

“Kirkland’s group dismisses the correlation with dated rocks on the grounds that these rocks haven’t been dated themselves. However, they are directly associated with nearby rocks that have been,” Brenner asserts.

Citing significant advancements, Kirkland asserts that his team has directly established the age of the minerals within the impact rock itself. “The young age argument continues to rely on correlations of undated rocks, primarily through satellite-based mapping. We now have two mineral clocks of the same age derived from the impacted rock itself, showcasing the importance of direct dating,” he states.