The Araona people wanted $1 million before they would let the NASA scientists pass through their territory in the remote Bolivian Amazon. Given a budget of $20,000 for their entire expedition, the scientists resorted to negotiating, and the indigenous people eventually agreed to a payment of $500, plus 500 rounds of .22 ammunition and 200 D-cell batteries.
"They couldn't be Eveready; they had to be Rayovac," recalls Compton Tucker, an earth scientist from NASA's Goddard Space Flight Center.
Unfortunately, the discussions stalled the group a week and by the time they reached the Iturralde Crater in October 1998, the rainy season had started and flooding prevented them from completing their research.
Four years later, Tucker and his colleagues have returned to the site to finish their work. This time, he says, "we know what to expect."
able --> In an interview in early September before he left for Bolivia, Tucker said email reports from the pre-expedition negotiations with the Araona indicate that they want a motorized canoe, two extra motors and an office, rent paid, in the nearby town of Riberalta.
The price is worth it to Tucker and the other researchers on the expedition, in full swing this week, because of the significance of the questions they could answer.
Unknown cause
Scientists are not certain how or when Iturralde Crater formed (despite its name that alludes to an impact). General speculation and circumstantial evidence point to the collision of a meteor either an asteroid or comet -- about 5,000 to 30,000 years ago. This would make it one of the youngest impact craters known, although some scientists argue it is much older.
If the crater is young, it may correlate to climatological events in Earth's history or to a known extinction event. It may even be included in the folklore of some South American native tribes.
"Or it's just an odd, perfect round hole on the face of the Earth and you have to start thinking about extraterrestrials or something," jokes Tim Killeen, a conservation biologist who will lead the trek.
Killeen, a research fellow with Conservation International, has been living in Bolivia and working with the Noel Kempff Mercado Natural History Museum in Santa Cruz for about the last 18 years. He first met Tucker when, he says, "about seven or eight years ago, these guys from NASA started coming down and bothering me to help them interpret their satellite imagery."
Despite Killeen's familiarity with Bolivia, the expedition team needs the assistance of the Araona to reach the Iturralde Crater, not just to pass through their land, but to serve as guides. The locals will also help blaze the 9-mile (15-kilometer) trail to the crater, which caps a trip involving rides in a jet, a motorboat, a dugout canoe and a helicopter (courtesy of the Drug Enforcement Agency).
But it isn't the craters remote location that contributed to scientists late identification of Iturralde as a possible impact site in 1985. Rather, its features are very subtle.
Unlike Meteor Crater, a gaping hole 550 feet (170 meters) deep in the Arizona bedrock, the elevation at Iturralde changes by no more than the height of a small child. It is difficult to spot in an area that spans 5 miles (10 kilometers). Yet a nearly perfectly circular pattern, due to differences in vegetation, stands out in Landsat images taken from space.
Washing away evidence
Iturraldes subtle features may be due to its location. Erosion is quick in the wet, rainforest environment.
If the crater is still visible, some scientists say, it cannot be much older 30,000 years; otherwise it would have completely eroded away.
The challenges in identifying the crater are many. The soil in rainforests is very deep. There is about 2 miles (3 kilometers) of it covering the bedrock that's under Bolivia. An impact would have ejected that material into the atmosphere, but some of it would have slumped back into the temporarily gaping hole over time.
"It was more like a big splat," Tucker says, in reference to other impacts that expend most of their energy blowing up bedrock.
All this makes the researchers job more difficult. They will still search for the usual, expected rocks and glass particles (called shocked quartz) associated with impacts, but this material may have eroded away. The scientists will take soil core samples to analyze for increased levels of elements that are found in more abundance in meteors than on Earth. One of these, iridium, can help distinguish whether a space rock was a comet or asteroid.
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