Share

Giant, ancient space rock helped shape Nevada

|
News,Science and Technology

LAS VEGAS (AP) — Way back in time before humans or even dinosaurs roamed the planet, a huge extraterrestrial object plunged into a sea on the edge of a continent in what's now eastern Nevada.

It flung colonies of eel-like critters to the rim of the impact crater when tsunamis sloshed across a shallow shelf.

Geologists who for years have been studying a remnant of the rim encrusted with tiny teeth fossils on Tempiute Mountain know this happened 382 million years ago.

And, they know the object came from outer space, much like the 55-foot-wide, 10,000-ton meteor that exploded over Russia on Feb. 15, showering pieces down on the Ural region and injuring 1,500 people.

But the geologists who focused their work on Nevada more than 20 years ago still are looking for ground zero of the horrendous impact that left limestone-and-fossil debris known as the Alamo Breccia, 90 miles north of Las Vegas. This chunk of what they think is the crater's rim is about the size of the Empire State Building lying on its side.

"Something came down and dug a hole in the ground and shook things up," John E. Warme, professor emeritus at the Colorado School of Mines, told the Las Vegas Review-Journal (http://bit.ly/YPT3iu).

"We don't have something that is clearly ground zero, and that's been really frustrating," he said.

He added that much of the challenge is because "the geology is so complicated since that time. There's been so much mountain building, and uplifting and shifting around of the crust of the Earth."

Another factor, he said, has been gaining access to explore geologic clues in Area 51, the classified, Defense Department installation along the dry Groom Lake bed where the military tests high-tech aircraft not far from the Extraterrestrial Highway and the rural town of Rachel that sits in the shadow of Tempiute Mountain.

"It's just pure coincidence, the fact that Area 51 is there and there is the legendary stuff about space aliens," he said.

In an email, Warme elaborated: "The fact that Tempiute Mountain is in sight of the Extraterrestrial Highway is a remarkable coincidence. The Alamo event and anything to do with Area 51 is purely coincidental. However, there are key rock outcrops on Area 51 that we would like to investigate but are 'forbidden.'?"

BIG SPACE ROCK

Warme said the Alamo event shook a widespread area when the space rock slammed into Earth. It probably sent tidal waves emanating from shallow waters above a limestone platform in the east toward a deeper sea in the west.

"It was certainly caused by the impact of an extraterrestrial body," he said.

Unlike the celestial event in Russia in mid-February that he said was caused by "part of an asteroid or comet, a piece of something in space that was screaming along," the one that barreled into ancient Nevada was much bigger.

Warme's colleague, the late San Diego State University geologist Jared R. Morrow, estimated the Alamo impact object was several hundred feet in diameter. Based on other craters geologists have observed, he calculated the resulting crater to be at least 1 mile deep and between 40 and 60 miles in diameter.

"We see the currents went back and forth and redistributed the Alamo Breccia," Warme said. "The currents moved debris around and they might have been tidal waves."

When the space rock hit, it spread a debris layer over a few hundred miles from what is now Eureka in the north to Yucca Gap south of the impact area and just north of the Las Vegas Valley.

"Not long ago we discovered a zone of rocks exposed on Frenchman Mountain, due east of Las Vegas, that we have interpreted as disturbance from seismic waves that traveled far from ground zero," Warme said.

Since the impact, there has been folding and faulting and the layer has been observed in 25 different mountain ranges.

"When you drive through Nevada, you see all these layers of tilted rock. We know it absolutely correlates," Warme said, adding, "Each one of the rock layers tells a story."

HOW THEY KNOW

On a field trip to the Western Pahranagat Range in 1993, Warme and geologist Charles A. Sandberg chipped away at gray, limestone slabs that were once part of an ancient sea floor but are now high and dry.

Sandberg, a U.S. Geological Survey expert on microscopic fossils, was collecting the toothy remains of microscopic, prehistoric eels called "conodonts."

At the time he estimated the eels were from the Devonian period, 375 million years ago when primitive fish dominated the sea and the first sharks, insects and amphibians appeared.

About 100 million years earlier — 470 million years ago — a city-block-size asteroid collided with what is now northern Iowa, leaving a large crater about the time early life forms began to thrive in the oceans.

Bevan French, an adjunct scientist at the National Museum of Natural History, recently showed microscopic evidence of quartz that was shocked by the impact. The crater later filled with shale and sediment bearing sea-creature fossils.

For comparison, dinosaurs didn't appear until 200 million years ago and disappeared about 66.2 million years ago when scientists believe an asteroid, 6.2 miles wide, hit the Yucatan Peninsula in southeastern Mexico. That catastrophic event wiped out dinosaurs and the food they ate, and changed the climate.

Humans wouldn't evolve until about 2 million years ago.

Since 1993, Sandberg has refined the Alamo Breccia time period to 382 million years ago from the mix of conodont species it contains based on new work with similar fossil zones in the world and radioactive dating of the rocks.

Warme said Sandberg and others have dissolved hundreds of pounds of Alamo Breccia rocks in acid hoping to find pieces of an impact object. Through this they have turned up grains of quartz. Looking through an electron microscope, they have observed evidence the quartz had endured shock.

"That was one of the confirmations that this was an impact and not some other catastrophic event," Warme said.

He said Sandberg is still exploring the breccia "far west of the Alamo town area, looking for ground zero."

PHONE HOME, E.T.

Previously reported evidence by Warme and Sandberg points to a meteorite that created the Alamo Breccia. Some rocks from the limestone debris are studded with so-called fool's gold and other iron-based minerals that might have a link to meteorites.

Still other rocks found near the breccia are speckled with unique grains of quartz that were perhaps loosened from bedrock.

Geologists have also detected iridium in the vicinity, a metal that is relatively rare in the Earth's crust but is more commonly found in meteorites.

Warme, 76, who still makes periodic field trips to the site, is fascinated that for reasons that deal with lore instead of science, the lone paved road that threads the middle of this sprawling, outdoor laboratory was officially named the Extraterrestrial Highway in 1996.

"I'll be darned what looks like the closest location to ground zero is Tempiute Mountain, and you look over from the mountain and you see Rachel. It just makes me smile," he said.

"I joke with people. Just beyond Rachel you see all those circular patches," he said, referring to the green alpha fields that sprout from circular water sprinkling systems.

He tells them, "That's where the little green men landed and that's from their rocket exhaust."

___

Information from: Las Vegas Review-Journal, http://www.lvrj.com

View article comments Leave a comment