Meteor Crater

Yesterday (Wednesday) we visited another big hole in the ground, this one not formed from earth’s natural processes, but from something extraterrestrial.

Meteor crater was formed 50,000 years ago when an iron-nickel meteorite (meteors stay in the sky, meteorites hit the ground) struck what is now the Arizona desert. The meteor is estimated to have been about 150 feet across and weighed several hundred thousand tons (a 2-foot wide, 1,400-pound fragment of it is pictured, above left). It struck the land with an explosive force greater than 20 million tons of TNT. During the crater’s formation, over 175 million tons of rock were thrown out a distance of over a mile. Large blocks of limestone, the size of small houses, were heaved onto the rim and flat-lying beds of rock were overturned or uplifted as much as 150 feet.

The crater made a hole in the rocks of the Kaibab Limestone and Coconino Sandstone from 260 million years ago. The crater is over 4,000 feet across and 550 feet deep. Originally, the crater is thought to have been 700 feet deep (as tall as a 70-story building) but erosion has transferred the topsoil over time. The circumference is 2.4 miles.

How do scientists know that the crater isn’t a volcanic caldera? After all, people argued over its origin when it was first discovered in 1871. Local settlers just thought it was part of the Hopi Buttes volcanic field northeast of the site. After many years of study, scientists have concluded that it is definitely not volcanic and that it is the result of an impact. There is the presence of many meteorite fragments on the northeast side of the crater. Plus, two minerals: coesite and stishovite were present in the rocks, both high-pressure forms of quartz that were altered by the extremely high pressure of the impact. These minerals are not found in volcanic craters or rocks.

During 1964 through 1972, the US Geological Survey and NASA provided science and sampling training for the Apollo astronauts because scientists were interested in what kind of materials might lay on the moon’s surface and below.

Collisions have occurred since the beginning of the solar system and will continue to occur. Collisions the size of the one that hit Meteor Crater average every 50,000 years. It’s time for another one so luckily scientists are “looking” to the skies with their high-powered digital telescopes.

Some information came from what I learned from the museum displays and from a pamphlet handed out at the fee station called, “Meteor Crater: Brief History.”