Nature Notes: Astroblemes

BY CATHRYN HOYT

What are the chances that a killer asteroid might land in west Texas? If the past is any clue, perhaps  better than you think.

Between Marathon and Fort Stockton, You’ll find a bowl-shaped depression. Further on is a ring of hills. These hills, the bowl-shaped depression and the near-by Sierra Madera are mountains collectively known as an “astrobleme” or a scar left on the surface of the earth by an asteroid impact.

The Sierra Madera was formed about 65 million years ago by an asteroid exploding above the plains. The explosion’s shock waves created a crater about 8 miles in diameter. Rock from the crater was thrown up and out creating the ring of low hills that surround the Sierra Madera.

The Sierra Madera itself was created when the center of the crater was uplifted over 4000 ft. into a dome-like structure. 65 million years of erosion has removed any of the materials directly related to the explosion, weathered the dome into hills, and filled much of the crater with sediment.

Sierra Madera is on private ranch land, but nine miles southwest of Odessa you can visit a meteor crater that’s second largest in the U. S., sixth largest in the world.
The Odessa Crater was formed about 25,000 years ago when a shower of nickel-iron meteorites collided with the earth leaving impact and explosion craters spread across a 2-mile area. Research indicates that the Odessa Crater was created by a meteor over 50 feet in diameter. Over 100,000 cubic yards of crushed rock were ejected from the crater by the energy released at impact, creating a funnel-shaped depression approximately 550 feet in diameter and about 100 feet in depth. 

Geologists believe that the meteorite was traveling at such a high rate of speed that it exploded and vaporized upon contact with the earth’s surface creating an explosion crater rather than a true impact crater.

The site, now designated as a National Natural Landmark, has a small museum, visitors’ center and other features.

About 10 years ago, residents in Monahans saw a 2.5 pound meteorite fall to earth about 25 feet from a group of boys playing basketball. When they found the meteorite, it was still warm to the touch and burned black.

Although ordinary-looking on the outside, when the Monahans meteorite was cracked open, researchers discovered purple extraterrestrial salt crystals with tiny pockets of primordial water trapped inside. The first water ever recovered from space.

Chemical dating of the crystals revealed that the salt was formed 4.56 billion years ago, thus aging the water trapped within the crystals to the very beginning of our solar system. Where did water come from? Did it form in interstellar space and then travel into our solar system as ice in comets? Or did it form during planetary formation? 
These tiny droplets of ancient water have the potential to tell scientists much about the very origin of water. 
Nature Notes presents natural wonders of the Chihuahuan Desert in this column every other week. Nature Notes is produced by the Chihuahuan Desert Research Institute and Marfa Public Radio and is sponsored by the Meadows Foundation and the Dixon Water Foundation. Tune in to Nature Notes on KRTS-93.5 FM on Tuesdays and Thursdays at 8:35 a.m. and 4:45 p.m. and again on Thursdays at 7:06 p.m. Visit us online atnaturenotesradio.org.