John Roth shined his flashlight on a black streak flowing through the cream-colored marble forming the walls of the Oregon Caves.
The graphite line is graphic evidence of dramatic global warming that consumed so much oxygen that it nearly wiped out all life on the planet 247 million years ago, said the natural resources specialist for the Oregon Caves National Monument.
"It was the biggest extinction by far of all time," he said. "Geologists and paleontologists all agree on that. ... The extinction that killed the dinosaurs about 65 million years ago, that wasn't anything compared to this."
Yet, like the huge meteor striking the Gulf of Mexico that many scientists believe wiped out the dinosaurs, the global warming at the end of the Permian period resulted in deadly amounts of carbon dioxide that killed most land animals, he said.
Scientists aren't certain what caused the episode some 247 million years ago. They estimate that temperatures ranged in the low 100s year-round for thousands of years, he said.
"Its kind of scary that we don't know for sure what caused the worst catastrophe of life on this planet," he said.
The graphite lines, whose significance was recently recognized, are not unique to the caves, which were formed perhaps half a million years ago, he said.
Roth is a geologist by training and a former science teacher who has worked as a natural resource specialist at the monument for 17 years.
He said the new evidence suggests that "we had a runaway hothouse effect because of the excess carbon dioxide. There was so much carbon dioxide introduced into the atmosphere, mostly from methane from the oceans."
That carbon dioxide build-up alone would have killed off most oxygen-breathing species, he said.
With the annual caves tour season under way, this latest discovery will give guides yet another scientific topic to discuss with visitors.
Another is the fact a jaguar fossil found in the caves in 1995 was recently dated by a Canadian expert to be 32,800 years old, making it one of the oldest known jaguar fossils found in North America, Roth said.
Grizzly fossils thousands of years old were found in 1997 by a team mapping the far interior of the caves. Half a dozen previously undescribed species of insects, including a relic from the last Ice Age, also have been found there.