50,000 yr old Meteor Impact Crater near Flagstaff, Arizona.

Meteor Crater (aka Barringer Crater) is about 1 km in diameter and located an hour’s drive east from Flagstaff, Arizona.  Formed 50,000 yrs ago by the impact of an iron-nickel asteroid perhaps 50 meters in diameter.  Although seen by Barringer as an iron mining prospect, numerous attempts failed to find a buried iron mass from the impactor.  We now know that this is because the impact was at a speed high enough to vaporize the projectile as well as a large mass of the target sandstones, causing the crater-forming explosion.  Only small fragments of the projectile have been located.

Meteor Crater is especially important in planetary science as it is the prototype structure on which the essential features of craters, generally, were worked out by Gene Shoemaker.  Diagnostics of impact include highly shocked minerals (which can only form at pressures created in cosmic impacts) in the crater floor, shatter cones, and an over-turned rim-flap (caused by folding of the pre-impact strata by the blast, a bit like the petals of a giant flower unfolding as they open).

Although small, the impact was no doubt locally devastating to the surrounding plants and animals, showering the environs with hypervelocity rock and metal shrapnel and killing everything for 10’s of kilometers around.  The crater is about 200 times smaller than the one responsible for the KT extinction 65 Myr ago.  The projectile was similar in size to the one that caused an airburst above Siberia in 1906, but being of iron (instead of stone or ice) was able to deposit its energy into the ground).

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