Lens to the Natural World. Kenneth H. Olson
Читать онлайн книгу.
one twenty-four hour day with five-ton dump trucks would require a parade of more than 11 million of them. They would pass a given point at the rate of 125 per second! Thus, in the course of some 5 million years, the immense canyon was carved.
At Niagara Falls, the ledge over which the river flows is being cut back three or four feet per year, a process that means that the gorge is advancing upstream toward Lake Erie and in 25,000 years will reach it and empty the lake. Then, the other Great Lakes, one by one, will also be drained, becoming again the mere river valleys they were in an earlier epoch.
If a single picture could be taken every 100 or 500 years and put into a film to speed up the movement of what is happening, we would see the hills change shape like so many clouds. Time’s passage means change, oceans encroaching on the land, continents moving—transformation.
The Rocky Mountains did not always exist. In many regions, they are composed of layers that were once sediments accumulating on the floor of shallow seas from 350 million to 1 billion years ago. Those silts and limes hardened into rock and were then pushed upward at the rate of only an inch or so a year. Over 70 million years, the inches would add up to miles, but the mountains are now being eroded at least as fast as they rise. Again, these are the young mountains. All the truly ancient mountains are gone; whole ranges have been eroded away several times, a raindrop and a particle at a time . . . because the earth has an abundance of time with which to work.
“A thousand ages in Thy sight are like an evening gone,” sings an old hymn that echoes the Psalms. God has plenty of time. The physicist Freeman Dyson later occupied the position once held by Einstein at Princeton’s Institute for Advanced Study. In his book Infinite in All Directions, Dyson wrote, “Mind is patient. Mind has waited for 3 billion years on this planet before composing its first string quartet.”
4 / If These Bones Could Speak
The hand of the Lord was upon me, and he brought be out by the Spirit of the Lord and set me down in the midst of the valley; it was full of bones . . . and lo, they were very dry . . . So I prophesied as I was commanded, . . . there was a noise, and behold, a rattling; and the bones came together, bone to its bone . . . and breath came into them, and they lived, and stood upon their feet, an exceedingly great host.
Ezekiel
We could not know the extent of it at first, but the valley was indeed full of bones. More than twenty years ago, my fifth grade son, Garrett, and I were hunting dinosaurs on the prairies of the Great Plains, something we did for two weeks every summer vacation. Always in July, our trips coincided with the hottest weather when temperatures usually climbed to more than 100 degrees in the shade. (That’s something of a euphemism; there was never any shade.) We usually slept in tents, and the sudden, violent, mid-night thunderstorms generated by the heat often sent us running to the pickup cab, our path lit by near-constant lightning flashes, certain that without such refuge we would be blown away. It is all part of what one does to find fossils; however, it is pretty mild when compared to the challenges that confronted the earliest dinosaur seekers, those who explored the badlands with horses and wagons and were often days from the nearest settlements.
We camped not far from a two hundred-foot cliff overlooking a small river that had cut its winding, convoluted way down through the banded sedimentary rocks from the period of time that holds the last of the dinosaurs. The river now occupies a narrow bed that is sometimes reduced to a trickle, but it was not always such a diminutive stream, for it lies within a much larger, much more ancient channel, one of the countless channels for melt-waters from the last continental glacier. Twelve thousand years ago and some distance to the north, the front of the retreating ice would have been nearly a mile thick and waters a mile wide would have swirled and churned in the broad valley just beneath us.
Now, a herd of black cattle grazes down there in the distance; somewhat apart are several bison that a rancher has added to his operation, a practice that is becoming increasingly common in the West. A few cottonwoods dot the flood plain; most of them huge and dying, since new trees are dependant for propagation upon high water, which no longer comes due to the flow being retained and controlled by irrigation dams. A golden eagle rides the thermals above, making lazy spirals in the blue sky. Coyotes howl at first and last light; otherwise, the loudest sound is that of a bumblebee moving between coneflowers, intent upon its business, oblivious to ours.
Ours has to do with still another riverbed, over five thousand times more ancient, the cross-section of which has been exposed by erosion about a third of the way down the cliff. We had found miscellaneous fragments of bone at the bottom. When that happens, one follows the pieces upward, hoping to find the source. Perched on the side of the sixty-degree slope, hacking footholds and probing with picks and knives, the horizon that had been producing the eroded bone was revealed, and it exceeded anything we could have imagined. Wherever we probed at this zone of twelve inches in thickness, there was rust-colored bone—leg bones, ribs, foot bones, ossified tendon, vertebrae, and pieces of skull! The skeletal elements were log-jammed together at a density of about thirty bones per square meter. None of the bones were in place, hooked together as a skeleton; instead, they had been moved in high water and packed together in random fashion, i.e., they were disarticulated. I was interviewed by a newspaper concerning the site, and, when the article was published, it stated that the bones were inarticulate, which would mean they couldn’t speak. However, in their own way, they spoke volumes.
Thus, in addition to working ten hours a day at the excavation, the beginning or the end of a typical day often found one simply in contemplation of the mysterious world of the dinosaurs, more of which was beginning to be revealed with each shovelful of dirt. Regarding such moments, the world-famous paleontologist Robert Bakker writes in his 1986 book, The Dinosaur Heresies, “Reverie is normal in Wyoming at sunrise. I suppose a no-nonsense laboratory scientist, clad in his white lab coat and steely-eyed objectivity, might think I was wasting my time communing with the spirit of the fossil beast. But scientists need long walks and quiet times at the quarry to let the whole pattern of fossil history sink into our consciousness.”
We would return year after year to this same spot, each time cutting in several feet to excavate a platform where we could work to expose and map the extent of the dinosaur material. Then came the process of removing the smaller bones, digging around the larger ones and applying plaster jackets so they could be safely removed, hauling them by rope and stretcher up the steep incline. The huge extent of the bone-bed on the cliff face was now apparent: it was more than four hundred yards wide. After several summers of such exploration by just the two of us, a crew of college students and adults was assembled to work for two or three weeks each summer. A small front-end loader was employed to remove some of the overburden in a process that resembled terracing a road on the side of a mountain. Over the course of a dozen years, more than 6,000 dinosaur bones were removed from the site, and it is likely that acres more still remain in that side-hill.
All the bones are from a single species of dinosaur, the large hadrosaur, or so-called “duckbilled” plant-eater named Edmontosaurus. In addition, we found a number of shed tyrannosaur teeth, suggesting the scene had been a windfall for the carnivores. Bones of other species are absent, indicating that this does not represent a gradual accumulation at the site over time but is the result of a single event. Collections like this, composed of individuals of different sizes, from quite small to nearly forty feet long, provide evidence that such creatures must have traveled in large herds, perhaps in migration. In the Far North, entire herds of caribou may drown in the attempt to cross a wide river in flood stage, and it may be that something similar happened here with a mass kill of dinosaurs. After the carcasses began to decompose, another high-water event must have separated and jumbled the skeletal elements and moved them downstream, there to become packed together and covered by sediment. Locked in the darkness, they remained until another river would begin to expose them to the light of day nearly 70 million earth orbits later and in an utterly different world.
Part of the message of the bones is delivered where they are found, in place. It is a truism in paleontology that as much as half the important data from a specimen can be obtained from its context in the field, paying attention to the conditions under which it was deposited in its original environment. The specimen is then fully excavated and moved to a museum or university lab, where it is cleaned, hardened,