Earth’s Oldest Asteroid Crater Found in Western Australia

The Oldest Impact Crater on Earth

Australia has taken first place, yet again, for the oldest known asteroid impact. A recent paper published in Nature has found an asteroid impact that occurred 3.47 billion years ago. 

Discovery in Western Australia’s Pilbara Craton

In the rugged outback of Western Australia, geologists have uncovered the world’s oldest known meteorite impact crater. The site lies in the Pilbara Craton, an ancient piece of Earth’s crust famous for harbouring some of the planet’s oldest rocks. Specifically, the crater evidence was found in an area called the North Pole Dome, about 40 km west of the town of Marble Bar in the East Pilbara Terrane. This region of iron-red hills and greenstone belts has long been studied for clues to early Earth, but only recently did scientists realize it held a colossal secret from 3.47 billion years ago.

The discovery came when a team from Curtin University, led by Professors Chris Kirkland and Tim Johnson, was investigating Archean rock layers in the Pilbara. In May 2021, within just an hour of fieldwork at North Pole Dome, they spotted something extraordinary: peculiar cone-shaped formations jutting from the ancient metasedimentary rocks. These features, known as shatter cones, immediately raised eyebrows. Shatter cones are a tell-tale fingerprint of a meteorite impact – they are only known to form under the extreme shock pressures of a cosmic collision. Finding such structures in rocks that were already known to be ~3.5 billion years old was a eureka moment for the geologists. It suggested that a major meteorite strike had scarred the Pilbara ground way back in the Paleoarchean era, making this the oldest impact structure ever identified on Earth.

Shatter Cones: Proof of a Cosmic Collision

Shatter cones are literally rocks shattered into a conical pattern. Imagine the unbelievable pressure wave of an asteroid slamming into Earth – it travels downward and outward through the bedrock, splintering it in a distinctive way. The result is chunks of rock that have striations radiating from a point, often looking like jagged stone ice-cream cones or “inverted badminton shuttlecocks,” as one researcher described. The tips of these cones all point toward the impact site, effectively tracing back to ground zero of the blast.

At the Pilbara site, the shatter cones were exceptionally well-preserved, despite being 3.47 billion years old. They were found in a geologic layer called the Antarctic Creek Member, a part of the greenstone succession in the East Pilbara. Geologically, this layer sits beneath unshocked carbonate breccias and ancient pillow lavas (lava that solidified underwater), which helps pin down the timing of the impact. Those overlying volcanic and sedimentary layers have been dated to about 3.47 Ga, so the impact must have happened just before their deposition. In other words, we have a time capsule of rock surrounding the event – the floor rocks bear the shatter cones, and the “ceiling” is basalt lava that erupted on the seafloor soon after, sealing in the evidence and marking the impact’s age.

The presence of shatter cones is unequivocal evidence of an ancient impact. On Earth, only the incredible pressures from a meteoritic impact (or nuclear explosions) are known to produce these structures. This discovery answered a longstanding question: could any impact craters have survived from the Earth’s early Archean eon? Until now, the oldest confirmed crater was the 2.23 Ga Yarrabubba structure, also in Western Australia. The Pilbara finding blows past that record by over a billion years, proving that bits of Earth’s deep past impact history are still recorded in the rocks. As Dr. Tim Johnson noted, “before our discovery, the oldest impact crater was 2.2 billion years old, so this is by far the oldest known crater ever found on Earth”.

Tiny Spherules: Fallout from the Ancient Blast

Shatter cones weren’t the only evidence. In the same rock unit, scientists also identified spherules – tiny, rounded particles that are relics of vaporized rock. When a meteor hits with enough force, it can instantly melt and vaporize part of the crust. The molten droplets thrown into the air cool and solidify into small glassy beads that rain back down over a wide area. These millimetre-scale glass spheres get locked in sediment layers, forming what geologists call spherule beds. Finding a spherule layer alongside shatter cones in Pilbara was essentially a double confirmation of a huge impact event.

Impact spherules are important because they preserve geochemical clues about the impactor and the explosion. For example, a previous study led by Dr. Andrew Glikson had found a 3.46 Ga spherule layer in the Pilbara (Duffer Formation) enriched in elements like platinum, nickel, and chromium – a signature of asteroid material. In the new Pilbara crater study, the spherules within the Antarctic Creek Member are likewise interpreted as the fallout from a colossal impact around 3.47 Ga. Such spherule beds have also been found in South Africa’s Barberton greenstone belt of similar age, hinting that multiple giant impacts bombarded Earth in that era.

Interestingly, having both shatter cones (a proximal, on-site indicator) and spherules (usually a more far-travelled ejecta indicator) in the same formation suggests at least two facets of the event. It’s possible that one extremely large impact created the shatter cones at Pilbara’s North Pole Dome and flung debris globally (producing spherule layers as far away as South Africa). Alternatively, there might have been two separate impacts around a similar time – one that created the local crater, and another whose fallout also settled in the Pilbara sedimentsfile-vwtmhy64mjn53rjs8dphtg. Either way, the evidence paints a picture of a planet that was ferociously hammered by extraterrestrial blows in its youth.

To the naked eye, these spherules just look like tiny sand grains, but they are time-capsules of an apocalypse. Scientists analysing them in cross-section or under the microscope can see their once-molten textures and even chemical makeup. They have been described as “globally-distributed airfall impact ejecta” – basically, the ash of an Earth-changing explosion scattered to the windsfile-vwtmhy64mjn53rjs8dphtg. The Pilbara spherules help confirm that the 3.47-billion-year-old Pilbara event was not a localized fluke, but part of the broader meteoritic bombardment Earth endured in the early Archean.

A Massive Asteroid and a 100-Kilometer Crater

How big was the monster that struck the Pilbara 3.47 billion years ago? The geological clues suggest it was enormous. The energy required to produce a 100-km wide crater in ancient, hard crust is mind-boggling. From the shatter cone orientations and other modelling, the researchers infer the meteorite hit at around 36,000 km/h (about 10 km/s). At that speed, much of the impactor’s kinetic energy would have been released as an intense blast wave and heat upon impact.

The crater created is estimated to be on the order of 70–100 kilometres across – a true gaping wound in the young Earth’s surface. (For context, the asteroid that killed the dinosaurs 66 million years ago was about 10–15 km in diameter and left a ~150 km crater in Mexico. So, we’re dealing with a comparably gigantic impact.) The Pilbara impact was described as a “major planetary event” by the scientists. It would have shaken the entire planet, causing magnitude >10 earthquakes and likely triggering tsunamis if ocean water was nearby. Debris ejected into the sky would have rained down across the globe – in fact, the presence of spherules in the Pilbara and possibly on other continents means material from the blast did spread worldwide.

Although the exact size of the asteroid is not yet known, we can make an educated guess. Based on crater scaling laws, an impactor on the order of several kilometres across (perhaps ~10 km) could produce a 100 km crater, depending on impact angle and the nature of the crust. Some scientists have speculated that impacts in the mid-Archean could even involve objects tens of kilometres wide. In one documented case, a ~25 km asteroid impact around 3.46 Ga was hypothesized from spherule evidence, which would have left a crater hundreds of kilometres wide. The Pilbara impact may not have been quite that cataclysmic, but it was certainly among the largest known in Earth’s history.

To put the energy release in perspective, consider that the Chicxulub impact (dinosaur-killer) released an estimated $10^8$ megatons of TNT equivalent energy. The Pilbara impact, with a crater possibly 2/3 the size, would be in that same order of magnitude of devastation. It essentially would have been a regional sterilization event – any existing life or ecosystems in the vicinity stood no chance in the face of such an explosion. The immediate blast would vaporize rock and boil seawater. The shockwave and thermal pulse would devastate hundreds of kilometres beyond the impact. We are talking about an event that makes all historic volcanic eruptions and earthquakes pale in comparison.

Earth 3.47 Billion Years Ago: A Different World

The world in which this gigantic impact occurred was starkly different from today’s Earth. We’re in the Paleoarchean, roughly a billion years after the planet formed. Geological studies indicate that around 3.5–3.47 Ga, Earth’s surface may have been dominated by ocean with only a few small proto-continental landmasses poking out. The Pilbara Craton itself was one of those early continental fragments – essentially a cluster of volcanic islands or domes that had solidified out of Earth’s primordial crust. Much of the area was likely under a shallow sea, as evidenced by pillow basalts (lava that cooled underwater) and ancient sedimentary rocks. Thus, the 3.47 Ga Pilbara impact likely struck a marine environment or a coastal area, creating a transient crater that may have been partially in water.

The atmosphere at that time would be unrecognizable to us. There was virtually no oxygen gas in the air. Instead, the sky was likely filled with carbon dioxide, nitrogen, water vapor, and methane. Scientists think a methane-rich haze might have given the sky an orangish tint, and the greenhouse effect of CO₂ and CH₄ kept the climate warm despite the faint young Sun. This was long before any land plants or even algae – the only life, if present, was microbial. In fact, 3.47 billion years ago is around the time we find the earliest evidence of life on Earth. Fossilized microbial mats (stromatolites) have been discovered in Western Australia dating to about 3.48 Ga, and other geochemical signs suggest life was emerging by 3.5 Ga. These primitive life forms lived in the oceans, perhaps around hydrothermal vents or shallow reefs, and were anaerobic (they did not require oxygen).

It’s sobering to think that while these pioneering microbes were eking out a living, a mountain-sized rock from space suddenly plunged into their world. The impact would have had global consequences even in an oceanic world. Immediately, it would send towering tsunami waves rippling across the seas. A blinding fireball would heat the sky, and molten rock droplets (the spherules) would rain down far and wide. The explosion would eject millions of tons of pulverized rock and dust into the atmosphere. Given the lack of oxygen, there were no wildfires (no forests yet!), but the blanket of ejecta could have darkened the skies worldwide. For days, maybe weeks, the sky might have glowed from falling debris, and for years after, a veil of dust could have altered the climate. Earth’s surface, largely ocean, might have seen short-term “impact winter” conditions – cooler temperatures due to sunlight blocked by haze – followed by longer-term warming as greenhouse gases like water vapor and CO₂ released by the impact circulated.

Aftermath: Shaping the Crust and Atmosphere

Beyond the immediate cataclysm, a collision of this scale would leave lasting marks on Earth’s geology and potentially its atmosphere. The Pilbara impact didn’t just punch a hole in the ground – it would have shaken the crust and mantle beneath. Models of large impacts suggest that such events deliver enormous thermal energy to the planet’s interior. Upon impact, much of the meteor’s kinetic energy is converted to heat, creating a superheated zone in the crust and upper mantlefile-vwtmhy64mjn53rjs8dphtg. In the case of the 3.47 Ga impact, the floor of the crater would have been composed of shattered, melted rock, with temperatures soaring for some time after the event.

One hypothesis is that giant impacts can kick-start tectonic processes. The authors of the Nature Communications study note that an impact >10 km in size can “instigate subduction zones and deep mantle plumes” on a young planet. In practical terms, this means the Pilbara impact might have helped push part of the Earth’s crust downward (initiating a primitive form of plate tectonics in that locale) or caused hot mantle material to well up. Professor Kirkland explained that the tremendous energy could have “played a role in shaping early Earth’s crust by pushing one part of the crust under another, or by forcing magma to rise from deep within the mantle”. Essentially, the impact could have given Earth’s crust a violent nudge, possibly contributing to the formation of the Pilbara Craton itself – cratons are the ancient stable cores of continents, and their origins are still debated. This find supports the idea that some cratons might owe their existence, in part, to big impacts providing the right conditions for crustal melting and stabilization.

The impact would also have created a substantial hydrothermal system. Once the dust settled, literally, the newly formed crater basin would have been a hotspot (both geologically and figuratively). Seawater or groundwater rushing into the deep, hot crater would heat up and circulate, likely forming networks of hot springs. These would be analogous to the hydrothermal pools and vents we see in places like Yellowstone or on mid-ocean ridges – but on a gigantic scale. Such post-impact hot pools could last for thousands of years, leaching minerals from the rocks and creating rich chemical brews. Intriguingly, scientists think impact craters can be cozy habitats for microbes once things cool down a bit. Kirkland pointed out that impact craters potentially created “environments friendly to microbial life such as hot water pools” that could have helped life get started. In the early Archean, life was only microbial, so a crater’s aftermath – warm water circulating through fractured rocks, bringing up nutrients – might have been an oasis for early life to thrive or even originatefile-vwtmhy64mjn53rjs8dphtg. It’s possible that not long after the annihilation caused by the Pilbara impact, new communities of microbes moved into the steaming crater walls, feeding off the chemical energy there.

On the atmospheric side, research suggests that frequent large impacts could have influenced the evolution of Earth’s air. A 2021 study proposed that the cumulative effect of many impacts in the Archean could have delayed the rise of oxygen in the atmosphere. Impacts vaporize a lot of rock, which can release reduced gases that consume oxygen, and, they blow off parts of the atmosphere and ocean into space or chemical sinks. The Pilbara impact by itself would inject huge amounts of water vapor and CO₂ (from limestone vaporized) into the air, possibly causing a short-term greenhouse warming. Conversely, sulphate aerosols from vaporized sea water could induce cooling. These complex effects are still being unravelled, but it’s clear that big impacts didn’t leave the atmosphere unchanged. One intriguing line from the 2021 study: early bombardment was an important “sink of oxygen,” implying that life’s attempts to oxygenate the air (via photosynthesis) may have been repeatedly set back by impact after impact. Thankfully for us, the barrage eventually eased off. The Pilbara crater, being the oldest known, might mark one of the last truly giant hits from the tail end of the Late Heavy Bombardment-like conditions. After about 3.5 Ga, it appears such enormous collisions became less frequent, allowing Earth’s surface to calm down a bit and life to gradually expand.

Significance: Earth’s Oldest Crater and Early History

Finding a 3.47-billion-year-old impact structure is like winning the geological lottery. It provides scientists a tangible window into a nearly inaccessible period of Earth’s history. For decades, researchers have asked: “Where are all the Archean craters?” We knew from the Moon’s pockmarked face that Earth must have been struck countless times in its first billion years – yet almost no craters older than 2 billion years had ever been found, presumed erased by time. The Pilbara discovery finally answers that question with a concrete example. It tells us that some traces of those ancient cataclysms do survive, if we know how to recognize them. This crater “provides a crucial piece of the puzzle of Earth’s impact history” and suggests there may be many more ancient craters awaiting discovery. In other words, the early Earth wasn’t as completely resurfaced as we thought – the geological record from the Archean Eon can still hold surprises.

The discovery is also significant for understanding the early Earth environment and the conditions under which life arose. It’s astounding that the Pilbara region – which has given us the earliest microfossils and stromatolites – also yields the oldest meteorite crater. This juxtaposition raises fascinating questions: Did frequent impacts help spark life by providing energy and creating niches like hydrothermal systems? Or did they challenge early life, causing repeated extinctions and setbacks? Perhaps both are true. This find will inspire new research into the co-evolution of Earth’s surface and life. As Prof. Johnson noted, such ancient impacts have been “largely ignored by geologists” until now, but they could hold keys to understanding how early continents formed and how life’s earliest habitats were shaped.

Moreover, studying this crater can inform us about the frequency of impacts back then. If one large crater is now identified in rocks ~3.5 Ga, there are likely others of similar age that simply haven’t been recognized or have been deformed. Geologists will no doubt revisit other Archean terrains with a fresh eye (and perhaps new technology like gravity surveys or drill cores) to hunt for more shatter cones or impact ejecta. Each new discovery will help calibrate the impact rate in Earth’s youth. It appears that big impacts were much more common in the Archean than in later geologic time. Earth’s early years were extraordinarily violent – a fact that has implications for everything from the formation of the crust to the origin of the oceans and atmosphere.

In summary, the unearthing of the 3.47-billion-year-old Pilbara crater is a landmark in geology. It pushes Earth’s known impact record over a billion years further back, into a time when our planet was a water-rich but alien place under a dim young Sun. The scientific evidence – shatter cones pointing to a blast epicentre, and microscopic spherules sprinkled in ancient sediments – reads like forensic evidence from a primordial crime scene, confirming a colossal asteroid strike. This event would have carved out a 100-km crater, rocked the planet’s crust, and possibly set the stage for geological processes and habitats that influenced early life. The broader significance reaches beyond just one crater: it opens a new frontier in studying the Hadean and Archean eons. As researchers continue to investigate this site and search for others, we’ll learn more about how cataclysms from above helped shape the Earth beneath our feet, and how life managed to survive and perhaps even benefit from these fiery trials in our planet’s infancy. The Pilbara crater is a profound reminder that even in Earth’s most ancient rocks, there are stories yet untold – in this case, the story of Earth’s oldest known thunderbolt from the sky, recorded in stone for eons, waiting for us to read it.

Here's the video we made on The Earth's Oldest Asteroid Crater Discovery on the OzGeology YouTube Channel:

Reference:
Christopher L. Kirkland, Tim E. Johnson, Jonas Kaempf, Bruno V. Ribeiro, Andreas Zametzer, R. Hugh Smithies, Brad McDonald. A Paleoarchaean impact crater in the Pilbara Craton, Western Australia. Nature Communications, 2025; 16 (1) DOI: 10.1038/s41467-025-57558-3