Meteor Hit Oklahoma 100M Years Later Than Thought
🕐 8 min read | 🌍 Natural Wonders
🔒 Key Takeaways
- The Ames structure in Major County, Oklahoma is a roughly 16-kilometre (10-mile) wide impact crater buried under about 3 kilometres of sedimentary rock.
- For decades the crater was dated to the Early Ordovician, around 470 million years ago, based purely on the layers sitting above and below it.
- New geochronology work points to an impact tens of millions — potentially around 100 million — years younger than that long-accepted figure.
- The Ames crater is one of the only impact structures on Earth that has been commercially profitable, with fractured breccia reservoirs yielding millions of barrels of oil.
- No surface rim survives: the entire crater was discovered in 1991 only because oil drillers kept hitting bizarrely shattered rock.
Somewhere beneath the wheat fields of northwestern Oklahoma, nearly two miles down, lies a hole punched into the planet by something travelling faster than a rifle bullet. Geologists have known about it since 1991 — but a re-examination of when the meteor hit Oklahoma has upended the textbook date by an almost absurd margin. The impact may have happened roughly 100 million years later than scientists thought, and the implications ripple far beyond one buried crater.
The Hidden Crater Beneath Oklahoma's Wheat Fields
Drive through Major County, Oklahoma, and you will see nothing unusual — gently rolling farmland, grain elevators, pumpjacks nodding on the horizon. Yet almost three kilometres beneath your tyres sits a near-circular bowl roughly 16 kilometres across, with a shattered central peak rising from its floor like a frozen splash. This is the Ames structure, one of the best-preserved buried impact craters on the North American continent precisely because it was sealed under younger sediment almost immediately after it formed. Erosion never got the chance to scrape it flat; instead, shale and carbonate entombed it like a geological time capsule. Nobody suspected it existed until the late 1980s, when oil companies drilling the Arbuckle play began pulling up cores of pulverised, melted and chaotically jumbled rock that made no stratigraphic sense. By 1991, seismic surveys had traced the full circular rim, and geologists realised they were looking at the scar of a cosmic collision. The crater has no surface expression whatsoever — it is a wound you can only see in sound waves and drill core.
How Scientists Originally Dated the Ames Impact
With no exposed rim and no fresh meteorite fragments lying around, the Ames crater was dated the old-fashioned way: by stratigraphic bracketing. Geologists identified the youngest rock unit that the impact had clearly disrupted, then the oldest undisturbed unit draped over the crater, and reasoned that the collision must have occurred between the two. Drill cores showed the impact cutting into Cambrian–Ordovician Arbuckle Group carbonates, with the overlying Oil Creek Formation shale apparently filling the basin. That bracket put the event at roughly 470 million years ago, in the Early-to-Middle Ordovician — a date that found its way into the Earth Impact Database, textbooks, and decades of petroleum geology reports. Intriguingly, this placed Ames in the same window as a cluster of other Ordovician impacts linked to the breakup of a large asteroid in the main belt. The date was elegant, convenient, and widely repeated. It was also entirely dependent on the assumption that those overlying shales were deposited into an open crater rather than later faulted, slumped or injected into it.
🤔 Did You Know?
Oklahoma's Ames crater is so rich in trapped petroleum that a single well drilled into the shattered rock of its central uplift produced more than a million barrels of oil — making it arguably the only meteorite impact in history that paid for itself.
The New Evidence That Moved the Clock Forward
Modern impact geochronology no longer relies on which rock sits on top of which. Instead, researchers hunt for minerals that were physically reset by the heat and shock of impact — zircon and apatite crystals that record a new radiometric clock starting the instant the shock wave passed, along with shock-melted glass suitable for argon-argon dating. When these techniques are applied to impact breccias and melt rock from buried craters, the results frequently disagree with the stratigraphic estimate, and at Ames the disagreement is dramatic. Analyses of shocked material point toward an impact far younger than the Ordovician bracket, plausibly in the Devonian–Mississippian interval roughly 350 to 370 million years ago — on the order of 100 million years later than the accepted figure. If correct, the shale sitting inside the crater is not the crater's cap at all; it was dragged, faulted or injected downward during or after the collapse of the crater walls. That single reinterpretation detaches Ames from the Ordovician asteroid shower entirely and rewrites its place in Earth's timeline.
Why Dating a Buried Crater Is So Fiendishly Hard
An impact crater is, by definition, a structure built out of destroyed evidence. The projectile largely vaporises, the target rock is melted, brecciated and overturned, and the crater walls collapse inward within minutes, scrambling strata that took hundreds of millions of years to deposit. In a buried structure like Ames, geologists cannot walk the rim or sample a continuous outcrop; they are limited to pencil-thin drill cores spaced kilometres apart, plus seismic reflection profiles that image shape but not age. Hydrothermal systems activated by impact heat can circulate hot fluids for tens of thousands of years afterward, partially resetting some mineral clocks while leaving others untouched. Worse, later burial can heat apatite and other low-closure-temperature minerals enough to leak daughter isotopes, producing ages that are too young for the wrong reasons. Resolving all this requires multiple independent dating systems that agree — which is exactly why revisions like this one take decades to emerge.
What a Younger Impact Would Have Looked Like
Whatever the date, the physics was brutal. An object several hundred metres across, striking at perhaps 15 to 20 kilometres per second, released energy equivalent to many thousands of megatons — excavating a transient cavity in seconds before the floor rebounded into a central uplift of fractured granite. The shock wave would have shattered rock to depths of several kilometres and launched a curtain of ejecta far beyond the crater rim. If the impact occurred in the Devonian or Mississippian rather than the Ordovician, the target was a very different Oklahoma: a warm, shallow tropical sea near the margin of a continental shelf, teeming with crinoids, brachiopods and armoured fish. A marine or coastal strike would have generated tsunami-like surges and a thick blanket of resurge sediment, features geologists can now go looking for in the surrounding basin. The revised date also changes which extinction events and sedimentary anomalies could plausibly be connected to the blast. Timing, in impact science, is everything.
The Crater That Pumps Oil: Why Ames Is Unique
Most impact craters are scientific curiosities; Ames is a balance sheet. The violent shattering of the central uplift and crater floor created enormous secondary porosity — a labyrinth of fractures and breccia voids — while the crater's bowl shape created a perfect structural trap. Organic-rich shale deposited in the enclosed basin later matured into source rock, and the hydrocarbons migrated straight into the fractured rubble next door. Some wells drilled into the structure have been spectacular producers, with individual wells reported to exceed a million barrels, and the field has yielded many millions of barrels overall. This is why the Ames structure is studied far more intensively than its remote, buried location would otherwise justify: every well is a free core sample. It is also a template used worldwide to evaluate other buried impact structures as potential reservoirs. Ironically, the industry that accidentally discovered the crater is also funding the science that keeps rewriting its history.
What This Means for Earth's Impact Record
Earth's catalogue of confirmed impact structures numbers only around 200, a pitiful sample compared with the Moon's millions, because plate tectonics, erosion and burial erase the evidence. That makes every individual age critical: geologists use the distribution of crater ages to estimate how often large objects hit our planet and whether impacts cluster in time. If a crater as well-studied as Ames can shift by 100 million years, other stratigraphically dated structures may be wrong too, and apparent clusters could partly be artefacts of imprecise dating. Several recent re-dating efforts worldwide — including revisions to craters once blamed for mass extinctions — have had exactly this effect, loosening supposed cause-and-effect links. The scientific lesson is not that geologists were careless, but that bracketing a crater between rock layers is a hypothesis, not a measurement. As high-precision shock geochronology spreads, expect more textbook dates to quietly move by tens of millions of years.
Final Thoughts
The Ames structure proves that some of Earth's most violent events are hiding in plain sight — or rather, two miles beneath it — and that even settled scientific dates can collapse under better instruments. Keep watching this crater: as new shocked-mineral ages are published, Oklahoma's buried meteor scar may be reassigned yet again. What other craters under your feet have the wrong birthday?
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Frequently Asked Questions
Is there a meteor crater in Oklahoma?
Yes — the Ames structure in Major County, northwestern Oklahoma, is a confirmed impact crater roughly 16 kilometres (10 miles) wide. It is completely buried beneath about 3 kilometres of younger sedimentary rock and has no surface expression, so it was only discovered in 1991 through oil drilling and seismic surveys.
How old is the Ames impact crater in Oklahoma?
The traditional age, based on the rock layers above and below the structure, is about 470 million years (Early Ordovician). However, newer dating of shock-affected minerals suggests the impact may have occurred tens of millions of years later, possibly in the Devonian–Mississippian around 350–370 million years ago.
Can you visit the Ames impact structure in Oklahoma?
There is nothing to see at the surface — the crater lies nearly two miles underground beneath farmland near the town of Ames. The only physical evidence available is drill core stored in geological repositories and seismic data held by energy companies and the Oklahoma Geological Survey.
Why does the Ames crater produce oil?
The impact shattered the target rock into highly porous breccia and created a bowl-shaped structural trap. Organic-rich sediments later filled the crater, matured into source rock, and fed hydrocarbons directly into the fractured rubble, making Ames one of the few impact craters on Earth to become a commercially valuable oil field.
📚 Further Reading & Research Sources
The following journals and institutions publish peer-reviewed research on the topics covered in this article:
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Conceptual illustration / public-domain geological survey imagery; verify licensing before publication.
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