Friday, July 25, 1997 | 11:30 a.m.
But Russell VernonClark of the UC San Diego acknowledged Friday that he cannot be 100 percent certain.
He said his conclusion was - and is - "that the material appears to be of extraterrestrial origin and appears to be manufactured ... because of the non-naturally occurring isotopes we found, both the major and the trace elements."
Those isotopes were from the elements silicon, germanium, zinc, nickel and silver, he said Friday.
VernonClark had revealed his conclusions July 4 during a Roswell news conference, staged as part of the 50th anniversary celebrations of an alleged alien crash in New Mexico.
He had been quoted then as saying of the fragment: "It is impossible for it to be from Earth."
But on Friday, VernonClark insisted he was misquoted.
"I cannot imagine my having said that," he said.
Of the chance the fragment might be from Earth, he said: "It's not impossible, but it is extremely unlikely and improbable."
He said much study still needs to be done on the sample.
"In retrospect, with 20-20 hindsight, I would have preferred to have more work done (on the sample before releasing findings), but I stand by my conclusions," VernonClark said by phone from his home in Encinitas, Calif., near San Diego.
Since the July 4 news conference, VernonClark's work has been subjected to criticism by other scientists who say the fragment could be duplicated in any earthbound laboratory.
Scientists studying VernonClark's data, circulated on the Internet, said it has serious flaws.
"There's just a number of huge mistakes in that report, holes big enough to run a dump truck through," said Albuquerque physicist Dave Thomas.
Scientists also said the claim the material would be extraterrestrial because of its unusual characteristics doesn't hold up. They said its ingredients could be purchased from chemical supply houses and easily mixed in any university chemistry lab.
"You could do it here," said University of Kentucky chemist Rob Toreki. "There's no validity to what he's saying."
Sandia National Laboratories scientist Dick Coats said scientists can buy purified silicon of different isotopes from the U.S. Department of Energy's Oak Ridge National Laboratory in Tennessee.
To make an "unearthly" sample, Toreki and Thomas said, one could mix the Oak Ridge samples in a chemistry lab.
Among problems cited by Thomas were claims that the alleged 50-year-old spacecraft debris contained detectable amounts of the element germanium-75, a substance so radioactive scientists say it would decay into other elements in less than a day.
Television producer Paul Davids has said the fragment came from an unidentified person who claimed to have gotten it from the 1947 wreckage near Roswell.