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TITLE: Learning From Meteor Crater


[Photo: Meteor Crater]

The huge hole in the Arizona desert known as Meteor Crater was blasted out nearly 50,000 years ago by a 45-m (150-ft) wide meteorite traveling more than 40,000 kph (25,000 mph). The crater is the freshest, best-preserved impact structure on Earth.

Meteor Crater has become Earth’s foremost natural laboratory for learning about the fundamental geologic process of impact cratering. We’d have to travel to the Moon to find anything comparable. Meteor Crater abounds in classic signs of impact. Here’s what investigators have found there and what this evidence tells us about large collisions.




See caption at right.

Observation:
Rock layers that were once horizontal within the crater are now tilted up or overturned. Debris in the rim consists of the same rock found in the crater walls.

Conclusion
The crater was formed by an explosion that lifted the strata and excavated rock from the crater, depositing it in the rim.

 

See caption at right.

Observation:
In and near the crater, fragments of the rock quartzite are shattered and melted (white, powdery). Only a few original quartz grains remain (grey, clear). The crater also contains two rare silica minerals formed only under extreme pressure. This image is 60mm across.

Conclusion
Impact is the only known natural process at Earth's surface that can generate enough heat and pressure to produce these results.

 

See caption at right.

Observation
No giant buried meteorite has been found in the crater. But small meteorite fragments dot the surrounding plains, as do tiny metal spherules like these. This image is 30mm across.

Conclusion
Much of the meteorite vaporized at impact. The condensing vapor formed the spherules.

 


Can you tell which of these sandstone specimens from Meteor Crater was altered by the meteorite impact?

See caption at right.



This sample, with its crushed and melted sand grains, and no visible sedimentary layering, was shocked by the impact.

See caption at right.



This is an unshocked sample of the Coconino Sandstone. Notice that the sedimentary layers are still intact.


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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits