Ames Crater Impact Dated to 467 Million Years Ago

Scientists have revised the age of the Ames crater, an ancient impact structure in Oklahoma. New zircon dating places the meteorite impact at approximately 467 million years ago, about 100 million years later than earlier estimates.

The revised age places the impact in the Ordovician period and links it to an interval of unusually high meteorite activity. It may also bring the event closer to a later mass extinction, although the evidence does not show that the impact caused the extinction.

What Is the Ames Crater?

The Ames crater is an ancient meteorite impact structure in what is now Oklahoma. It is not a sharply defined bowl like Arizona’s Barringer Crater because erosion, burial, sediment accumulation and tectonic activity have altered the original formation.

Scientists identify ancient impact sites through multiple lines of geological and geophysical evidence, including:

• Shocked or fractured minerals.
• High-pressure changes in crystals.
• Melted and recrystallized rock.
• Breccia composed of broken rock fragments.
• Unusual geological layers.
• Circular structural patterns.
• Magnetic and gravitational anomalies.

The crater preserves evidence of a major extraterrestrial collision and helps researchers reconstruct North America’s geological history.

The impact occurred about 467 million years ago. The discovery and dating occurred much later. Therefore, “100 million years later” describes a correction to the crater’s estimated age, not a recent meteor strike.

The New Age Estimate

Earlier interpretations placed the Ames impact roughly 100 million years earlier in geological time. New research places it at approximately 467 million years ago, during the Ordovician period Source 1.

The revision is based on analysis of zircon, a durable mineral that can preserve geological information for billions of years. Zircon crystals may contain uranium, which decays into lead at a predictable rate. Measuring the uranium-to-lead relationship allows scientists to estimate when the crystal formed or when a later geological event altered it.

This uranium-lead, or U-Pb, dating method does not usually identify a single exact year. Instead, scientists calculate an age range and compare it with the surrounding rocks, impact evidence and regional geological history.

Zircon is especially useful in impact studies because collisions can fracture, heat or deform crystals. Researchers must determine whether a zircon records its original formation, later alteration or the impact itself. Multiple samples and crystals provide a stronger test than one isolated measurement.

The results connect the Ames crater to a period of elevated meteorite bombardment around 467 million years ago Source 7.

Why the Revision Matters

A new geological timeline

A 100-million-year revision changes the relationship between the impact and other geological events. Researchers can now compare the Ames crater with Ordovician rock formations, sediment layers and environmental changes more accurately.

An Ordovician impact

The Ordovician period lasted from approximately 485 million to 444 million years ago. It featured major marine diversification, changing sea levels and significant geological activity. Most life lived in the oceans.

The revised date allows scientists to compare the Ames impact with:

• Other Ordovician impact structures.
• Meteorite debris in ancient sediments.
• Changes in marine environments.
• Climate and sea-level variations.
• Possible atmospheric or ocean-chemistry disturbances.

The date supports a connection to broader meteorite activity, but it does not show that all impacts during this period came from one object or caused global environmental change.

A possible connection to extinction

The younger age may place the Ames impact closer to a later mass extinction event Source 9. However, timing alone cannot establish causation.

Researchers would need precisely dated impact debris, chemical anomalies in sediment, atmospheric markers and evidence of ecological disruption. Climate change, sea-level fluctuations, volcanism, ocean chemistry and other ecological pressures could also have influenced extinction patterns.

How Scientists Date Ancient Impacts

Scientists first determine whether a structure was created by an impact rather than by volcanic, tectonic or sedimentary processes. They examine shocked minerals, high-pressure crystal structures, melted rock, breccia and chemical signatures. Gravity and magnetic surveys can reveal buried circular structures.

Researchers then date minerals and rocks associated with the collision. Impact energy can heat minerals, fracture crystals, reset isotopic systems and produce new melt. Careful sampling is necessary to distinguish the impact age from a mineral’s original formation age or later alteration.

Geological dates can change when scientists obtain better samples, more precise instruments or improved models of mineral behavior. A revised date reflects stronger evidence; it does not necessarily mean that earlier interpretations were unreasonable.

Ordovician Meteorite Bombardment

The Ames crater’s revised age links it to a broader interval of meteorite bombardment around 467 million years ago Source 7.

One possible explanation is the breakup of an asteroid, which could have produced multiple objects with related compositions and impact ages. However, researchers have not established that the Ames crater came from a specific asteroid family. They would need to compare mineral and chemical signatures, meteorite types, impact ages and possible orbital histories.

The known record is incomplete because ancient craters can be buried, destroyed or overlooked. A group of impacts from the same period can nevertheless reveal changes in bombardment intensity across the Solar System.

What the Study Does Not Prove

The findings do not establish the meteor’s exact diameter, speed, angle or impact energy. They also do not prove that the Ames impact caused a mass extinction. A temporal relationship identifies a topic for further research but does not demonstrate cause and effect.

The impact did not occur in “modern Oklahoma” as a political or geographic region. It occurred hundreds of millions of years ago, when continents, coastlines and landscapes were different. “What is now Oklahoma” refers to the present-day location of the ancient event.

Key Takeaways

• The Ames crater formed approximately 467 million years ago.
• The revised age is about 100 million years later than an earlier estimate.
• Zircon dating links the impact to elevated meteorite activity during the Ordovician.
• The revision changes interpretations of Oklahoma’s geological history.
• The impact may have occurred closer to a later mass extinction than previously thought.
• Current evidence does not prove that the impact caused the extinction.
• The meteor’s size, speed, trajectory and energy remain unknown.

Frequently Asked Questions

When did the meteor hit what is now Oklahoma?

Current research places the Ames crater impact at approximately 467 million years ago, during the Ordovician period Source 7.

Why was the impact dated 100 million years later?

New zircon dating indicated that the impact occurred about 100 million years later than earlier estimates. Scientists combined uranium-lead measurements with geological context and impact evidence to refine the age.

What is zircon dating?

Zircon dating measures uranium decay into lead inside zircon crystals. Because zircon can preserve isotopic information for extremely long periods, it can help determine when rocks formed or when an impact altered them.

Did the impact cause a mass extinction?

The evidence does not establish that the Ames impact caused a mass extinction. The revised date may place it closer to an extinction interval, but timing alone does not prove causation.

What does the discovery reveal about Ordovician meteor activity?

The findings connect the Ames crater to increased meteorite bombardment around 467 million years ago. The cause and scale of that bombardment remain subjects for further study.