We’ve found the oldest meteorite impact crater on Earth in the Pilbara region of Western Australia. This crater is over 3.5 billion years old, making it the most ancient one known, predating others by more than a billion years. Our findings are shared in Nature Communications.
The crater appeared exactly where we expected, lending support to a theory about how the Earth’s first continents were formed.
The planet’s oldest rocks emerged over 3 billion years ago and primarily exist in the cores of today’s continents. Although experts are divided on how these rocks formed, they are widely recognized as important for various chemical and biological processes on Earth.
Some geologists believe these ancient rocks came from hot plumes rising from Earth’s molten core, similar to how wax rises in a lava lamp. Others suggest that they formed through plate tectonic processes, where rocks push against and slide underneath each other.
Both ideas differ, but they share a common theme: the loss of heat from within the Earth.
We think differently. A few years ago, we proposed that the energy needed to create the continents in Pilbara came from large meteorite impacts. These impacts would have sent massive volumes of material flying and melted the surrounding rocks, leading to the formation of thick volcanic blobs that became part of the continental crust.
Our earlier evidence relied on the chemical makeup of tiny zircon crystals, but we needed more visible proof to convince fellow geologists. Thus, in May 2021, we traveled from Perth for two weeks of fieldwork with the Geological Survey of Western Australia (GSWA) to search for the crater.
We started by looking at a unique rock layer called the Antarctic Creek Member, which forms the sides of a large dome about 20 kilometers wide. This layer is around 20 meters thick and mainly consists of sedimentary rocks amid basaltic lava. It also contains small spherules—tiny droplets created during impacts—that can come from anywhere on Earth.
After studying GSWA maps and aerial photos, we identified promising sites in the Pilbara and split up to explore the area, hoping to find evidence of the crater.
When we reconvened, we were thrilled to discover that each of us had found shatter cones.
Shatter cones are unique, branching structures formed only by meteorite impacts. They visually reveal the shock from these collisions, standing out like natural sculptures in the landscape.
Remarkably, it turned out that we were indeed on the floor of a colossal, ancient impact crater. Though we took some photographs and collected samples, we had to move on. Our main concern was determining the age of these shatter cones to confirm if we had truly found Earth’s oldest crater.
After further studies, we returned to the site in May 2024 for an extended examination. Shatter cones were plentiful, and we traced them across the Antarctic Creek Member for hundreds of meters. Our research indicated that a thick layer of basalt above them showed no signs of impact shock, confirming that the impact must align with the age of the Antarctic Member, which is 3.5 billion years old.
With this information, we confirmed that our discovery was indeed the oldest impact crater on Earth. This bolstered our theories about the formation of the continents.
Serendipity plays a key role in science. Other than the Traditional Owners, the Nyamal people, it’s likely that no geologist had seen these remarkable features since their formation. Like others before us, we argue that meteorite impacts are crucial to understanding our planet’s geological history, just as they are on our moon and other celestial bodies.
There may still be many ancient craters hidden within the cores of other continents. Discovering and studying them could revolutionize our understanding of early Earth and how giant impacts influenced both the land we inhabit and possibly the origins of life itself.
Check out this related article: Unveiling Secrets: How a Dusty Old Moth from a London Museum Sparked an Astonishing Taxonomic Discovery
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