CAVE JUNCTION — 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 nearly wiped out all life on the planet an estimated 247 million years ago, explained the natural resources specialist for the Oregon Caves National Monument.

"This tells us that something wiped out enough oxygen so that most species died out," said Roth, a geologist by training.

"It was the biggest extinction by far of all time," he added. "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 which 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.

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Scientists aren’t certain what caused the episode some 247 million years ago, although some surmise it may have been triggered from "mountain uplift and oxidation of coal beds at a time when there were few ocean basins on continental shelves for burying carbon dioxide-rich sediments," he said. Scientists estimate that temperatures ranged in the low 100s year-round for thousands of years, he said.

"It’s kind of scary that we don’t know for sure what caused the worst catastrophe of life on this planet," he observed.

The graphite lines, whose significance was recently recognized, are not unique to the caves but they do establish an estimated age of the marble formation, Roth said. The famous caves within the marble were formed perhaps half a million years ago, he said.

"And it has only recently been recognized in a lot of scientific papers that this is worldwide," he said of the telltale lines in other rock formations.

A former science teacher who has worked as a natural resource specialist at the monument for 17 years, Roth originally believed the lines in the caves were caused by too much salt in the seawater where the marble was formed. But the layers of salt or gypsum that would have backed up that theory haven’t been found, he said.

With the annual caves tour season having started Saturday, 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.

And there are the picturesque stalagmites and stalactites, Roth said.

"People like the formations because they are pretty with all the ‘hangy-downs’ and ‘sticky-ups,’" he said. "But the bedrock around the caves to me is more interesting than a lot of these formations."

Like the graphite lines, he said.

"There are no disturbances in these lines," he said. "You almost never see that in other types of sediments. Sediments normally tend to get churned up by all sorts of animals."

However, the graphite lines are merely the aftermath of the ancient global warming episode, he said.

"This didn’t occur right at the time of the great extinction," he said. "These lines are bacterial reefs, composed of bacteria and maybe some algae. By definition, a mass extinction is something that happens worldwide."

Geologists believe the extremely low oxygen content resulted in conditions at sea level not unlike today’s "death zone" found at 25,000 feet above sea level on Mount Everest, he said.

"We had a runaway hothouse effect because of the excess carbon dioxide," he said. "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.

Although scientists can’t date the graphite lines themselves, they had estimated the age by looking at other rocks from the same era that contain radiolarians, tiny creatures made of silica which live in oceans, he said.

Scientists are now looking for radiolarians inside the marble at the caves to come up with a precise timeline, he said.

"We’ve got to find something like radiolarians to tell us the precise age," he said. "We’re still doing the research. ... But we already know a very significant geologic event happened here."

Reach reporter Paul Fattig at 776-4496 or e-mail him at pfattig@mailtribune.com.