Petrified tree stumps on Specimen Ridge. Yellowstone National Park, June 2004.When I began Googling around for some quick info about the petrified trees on Specimen Ridge, I got a surprise: most of the hits that came up were from creationist websites. Yes, believe it or not, the young-earth creationists get all in a tizzy about Yellowstone's ancient forests. They're worth getting excited about, no doubt about that, because like most things fossilized, they give you a rare glimpse at a long, long vanished world.
The geologists who have examined the slopes of Specimen Ridge have identified at least 27 successive layers of forests, each destroyed and partially buried under volcanic ash from Mt. Washburn, then an active volcano. The estimate is that these layers represent some 20,000 years of growth/catastrophe/regrowth/catastrophe/regrowth, beginning some 50 million years ago.
If that seems like a long time ago, just remember that the Earth had already completed 99% of its current history by then. The dinosaurs were only recently deceased, the supercontinent of Pangaea had broken up, and the continents of the western hemisphere looked pretty much as they do now:
(Image via the Paleomap Project)Still, from our vantage point, a long-vanished world. The trees found in these buried forests have living relatives and, if their current environments are any indication, Yellowstone in those days was a warm, humid place comparable to present-day Georgia. There are plenty of redwoods in these forests, but also maple, sycamore, walnut, chestnut, oak, dogwood - even magnolia trees. It doesn't take too close a look at my photo to realize that nothing like these will grow there today. Judging from the fact that all of the fossilized roots (when they can be found) show horizontal development, none of these trees seems to have grown on a hillside; each forest occupied a fairly flat valley and was buried under another level accumulation of ash and mud, until the earliest layer was some 1200 feet deep. The silica in the ash was absorbed into the wood, causing the fossilization that has preserved the trees to this day.
That all of this should provide fodder for creationists comes as rather a surprise, but it seems to all trace to a single geologist named Harold Coffin (Ph.D. from USC in 1969). He appears to have been associated with the creationist Earth History Research Center at Southwestern Adventist University (where they have a single Department of Biology and Geology!), but isn't listed as a current faculty member, so I'm not sure where he is nowadays. But Coffin has published on Specimen Ridge, claiming that the trees must have been transported to their present location; he has also reported finding upright floating stumps in Spirit Lake at Mt. St. Helens, which he suggests would explain the standing trees in Yellowstone.
Not everyone agrees that the trees have been transported; in fact, I don't find that anyone else believes that Yellowstone's fossil trees came from anywhere but Yellowstone, allowing for some movement due to rapid lahars. But Coffin's work is all over the creationist websites, the same claims over and over again. Upright logs in Spirit Lake! Therefore the Flood! QED! It takes so little to make a creationist happy, particularly when you're talking about evidence.
But that's the general approach that creationists rely upon: pick out one little line of evidence, try to poke a hole in it, and then imagine that all of geology, paleontology, and biology would collapse along with it. Why petrified trees being carried to Yellowstone by flood waters or mud flows would prove a young earth is hard to fathom, but they're sure it's so.
If you really want to look at the trees in my photo and imagine that they floated there in a magic flood and came to rest in an upright position, go ahead; I can't stop you. I'll wait until some geologists who aren't under the influence tell me that it's so and, until then, use my imagination to picture beautiful hardwood forests filled with strange-looking animals (Uintatheriums, for example) walking across land that's going to get buried under volcanic ash, then get eroded away again until, 50 million years later, I can hike up a ridge and sit next to three of those very same trees. That's grander than any creation story I've ever heard.
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Main sources:
Erling Dorf, Petrified Forests of Yellowstone. National Park Service, 1980.
William J. Fritz, Roadside Geology of the Yellowstone Country. Mountain Press, 1985.
4 comments:
50 million years ago Denver was at sea level. Specter Ridge must have been only slightly above sea level at the time. Redwoods (currently) live between 5 and 30 miles from the sea, so Specter Ridge must have been almost coastal then.
What caused Denver and Yellowstone to now be so far above sea level? In the 90's it was discovered that plates rise and fall depending on upwelling and sinking currents in the mantle beneath them. These currents change over time, so the Indonesian (SE Asian) part of the Eurasian Plate is now under sea level due to sinking currents in the mantle underneath, though it was above sea level in the (geologically) recent past, and Denver and much of the western United States is a mile high because it sits atop an upwelling in the mantle.
This explains how the fossilized trees of Specter Ridge originally grew on a plain, near sea level, and near a coast (OK, I didn't explain that part - but it has to do with accretion at the edges of tectonic plates) and are now almost a thousand miles inland, a mile high, on a cliff, and in too dry a climate to support such moisture-loving forests.
I just looked it up. The Mt. Washburn caldera is only 600,000 odd years old. Not 50 million. So if the trees are 50 million years old, it was some other source of ash that buried them. (The Yellowstone hot spot is only dated to about 20 million years ago, at which time it was far to the southwest.) Yellowstone may have been near the subducting edge of the Juan de Fuca or Pacific plate 50 million years ago. Subducting plates often create volcanoes on the leading edge of the overriding plate. Specter Ridge would have been near the leading edge of the overriding North American Plate back then.
The caldera is only 600,000 years old, but there have been volcanoes at that locale from much earlier. The caldera, of course, dates from the most recent of the massive "supervolcano" eruptions, which began when the Yellowstone Hot Spot arrived from the southwest a couple million years ago.
The landscape was definitely lower then than it is today, with Dorf suggesting an elevation of around 3000 feet. The Northern Rockies began their uplift about 100 million years ago, so Specimen Ridge would have been well above sea level. Even with a warmer climate, today's 7000'-12,000' elevation wouldn't have supported this kind of warm weather vegetation, though, so it must have been lower (plus, the ash covering the fossilized forests is itself some 1200' deep). As far as I've heard, redwoods had a much greater range at one time and weren't limited to coastal regions lke they are today.
The caldera on which Mt. Washburn is located is 600,000 years old, but the oldest of the volcanic caldera within Yellowstone National Park boundaries is only 2.1 million years old. (http://www.nps.gov/yell/naturescience/eruptions.htm) The history of the Yellowstone hot spot has been traced back to 20 million years ago. It is indeed a violent history. Its tearing apart of the Juan de Fuco plate might be what has makes it so violent. (http://news.discovery.com/earth/yellowstone-hot-spot-shreds-ancient-pacific-ocean.html)
Perhaps the petrified trees are younger than 50 million years old? No, they date to the Eocene and Oligocene, (http://origins.swau.edu/papers/dinos/yellowstone/default.html) from 56 to 23 million years ago. So they are older than the Yellowstone hotspot is know to be. It was some other source of ash that buried those forests.
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