by John McPhee
No one knew where the bears went when they left the Gallatin Range. When they came back, they were covered with mud.
Catastrophism in another form presented itself that autumn when Jack Epstein was transferred to the office of the Geological Survey’s Water Resources Division in Alexandria, Louisiana. There was no position for Anita, and she could not have had a job even if one had been open, for it was a rule of the Survey that spouses could not work for the same supervisor. The Alexandria office was small, and included one supervisor. Her nascent geological career was suddenly aborted. She taught physics and chemistry in a Rapides Parish high school. In the summer that followed, she worked for the state government as an interviewer in the unemployment office. She did her geology when and where she could. Driving home from work, she saw people dressed like signal flags hitting golf balls on fake moraines.
Fortunately, her husband was even less interested in the water resources of Louisiana than she was in the unemployment interviews. They decided they needed Ph.D.s to improve their chances of working somewhere else. They enrolled at Ohio State, and in eastern Pennsylvania took up the summer field work that led to their dissertations. They did geologic mapping and biostratigraphy among the ridges of the folded Appalachians—noting the directional trends of the various formations (the strike) and their angles of dip, along a narrow band of deformation from the Schuylkill Gap near Reading to the Delaware Water Gap, and on toward the elbow of the Delaware River where Pennsylvania, New Jersey, and New York conjoin. The most recent ice sheet had reached the Water Gap—where the downcutting Delaware River had sawed a mountain in two—and had filled the gap, and even overtopped the mountain, and then had stopped advancing. So the country of their dissertations was filled with fossil tundra, with kames and eskers, with periglacial boulders and the beds of vanished lakes, with erratics from the Adirondacks, with a vast imposition of terminal moraine. Like the outwash of Brooklyn and the tills of Indiana, this Pennsylvania countryside helped to give Anita her sophistication in glacial geology, which was consolidated at Ohio State, whose Institute of Polar Studies trains specialists in the field. Glacial evidence was not, however, what drew her particular attention. The Wisconsinan ice was modern, in the long roll of time, in much the way that Edward VII is modern compared with a hominid skull. The ice melted back out of the Water Gap seventeen thousand years ago. Anita was more interested in certain stratigraphic sequences in rock that protruded through the glacial debris and had existed for several hundred million years. She would crush this rock, separate out certain of its components, and under a microscope at fifty to a hundred magnifications study its contained conodonts, hard fragments of the bodies of unknown marine creatures—hard as human teeth, and of the same material. At a hundred magnifications, some of them looked like wolf jaws, others like shark teeth, arrowheads, bits of serrated lizard spine—not unpleasing to the eye, with an asymmetrical, objet-trouvé appeal. Many of them resembled conical incisors, and in 1856 this had caused a Latvian paleontologist to give them their name. Conodonts were in many formations but were most easily extracted from limestone and dolomite—the carbonate rocks. They would become useful to geologists because they were all over the earth, and because the creatures that left them behind had appeared in the world early in the Paleozoic and had vanished forever at the end of the Triassic. Yet not until the late nineteen-fifties did studies begin to be published that brought conodonts to prominence as index fossils, helping to subdivide a specific zone of time, a fifteenth of the history of the earth, running from 512 to 208 million years before the present. As the conodont-bearing creatures evolved through those years, their conodonts became increasingly complex, with apparatus extending in denticles, bars, and blades. Geologists, observing these changes, could readily assign relative ages to the places where conodonts were found.
After collecting her samples, Anita could not have been shipping them back to a better place than Ohio State. Just as Johns Hopkins has been celebrated for lacrosse, Hartwick for soccer, and Rollins for tennis, Ohio State is known for conodonts. Geologists call Ohio State “a conodont factory.” Like all the other workers there (a specialist in the field is known in the profession as “a conodont worker”), she noticed incidentally as she catalogued the evolutionary changes in her specimens that some were light and some were dark. They were white, brown, yellow, tan, and gray. Since they were coming into Columbus from all over the United States, and in fact the world, she began to notice that in a general way their colors followed geographical patterns. She wondered what that might suggest. She looked at conodonts from Kentucky and Ohio, which were of a yellow so pale it was almost white. From western Pennsylvania they were jonquil, from central Pennsylvania brown. The ones she had collected north of Schuylkill Gap were black. She thought at first there was something wrong with her samples, but her adviser told her that in all likelihood the blackness was merely the result of pressures attendant when the limestone or dolomite was being deformed. He did not encourage her to make a formal study of the matter, and she returned to her absorptions with conodont biostratigraphy. On one of her trips east, she crossed New York State, collecting dolomite and limestone all the way. From Lake Erie to the Catskills, New York State is a cake of Devonian rock, lying flat in a swath sixty miles wide. You can travel across it chipping off rock of the same approximate age, and not just any old Devonian samples—for the Devonian period covers forty-six million years—but, say, limestone and dolomite from the Gedinnian age, which is seven million years of early Devonian, or even from the Helderbergian stage of middle Gedinnian time. For as much as a hundred and fifty miles, you could follow a line of time no broader than three million years. You could cut it that fine. Anita did something of the sort, and crushed the rocks at Ohio State. She noticed that the conodonts were amber in Erie County, tan in Schuyler and Steuben. They were cordovan in Tioga and Broome. In Albany County, they were dark as pitch.
She wondered what the colors might be suggesting about the geologic history of the region.
Nothing much, her adviser assured her. The colors were the results of tectonic pressures.
It had been just a passing thought. She let it go, and went back to work on her thesis, which would be titled “Stratigraphy and Conodont Paleontology of Upper Silurian and Lower Devonian Rocks of New Jersey, Southeastern New York, and Eastern Pennsylvania.” She was documenting subtle evolutionary differences in conodonts close to the Silurian-Devonian boundary, a point in time just over four hundred million years ago. And, arranging her microfossils in chronicle form, she was differentiating and cataloguing in time the units of rock from which they had been removed. This in turn would help her to understand the structure of the country in which she had picked up the rock. Conodont colors faded in her mind.
By 1966, having completed their course work at Ohio State, Anita and Jack Epstein had returned to work for the Geological Survey—he to concentrate on northern-Appalachian geology and she to take what she could get, which was a map-editing job in Washington. She would have preferred to work on conodonts, but the federal budget at that time covered only one conodont worker, and someone else had the job. Before long, she had become general editor of all geologic mapping taking place east of the Mississippi River. She dealt with hundreds of geologists. There were fifteen hundred in the Survey, and the quality of their work, their capacity for visualizing plunging synclines and recumbent folds, tended to vary. She looked upon some of them as “losers.” Such people were sent to what she privately described as “penal quadrangles”: the lesser bayous of Louisiana, the Okefenokee Swamp. If they did not know strike from dip, they could go where they would encounter neither. She did not feel pity. Better to be a loser in the United States, she thought, than to be a geological peasant in China. There are four hundred thousand people in the Chinese Geological Survey. “It’s a hell of an outfit,” in Anita’s words. “If they want to see exposed rock, they don’t depend on streambanks and roadcuts, as we do. If an important Chinese geologis
t wants to see a section of rock, the peasants dig out a mountainside.”
She was a map editor for seven years, during all of which she continued her conodont research, almost wholly on her own time. Collecting rock from Maryland and Pennsylvania, she crushed it and “ran the samples” at home. Running samples was not just a matter of pushing slides past the nose of a microscope. After pulverizing the rock and dissolving most of it in acid, she had to sort its remaining components, and this could not be done chemically, so it had to be done physically. It was a problem analogous to the separation of uranium isotopes, which in the early nineteen-forties had brought any number of physicists to a halt. It was also something like sluicing gold, but you could not see the gold.
Anita primarily uses tetrabromoethane, an extremely heavy and extremely toxic fluid that costs three hundred dollars a gallon. Granite will float in tetrabromoethane. Quartz will float in tetrabromoethane. Conodonts sink without a bubble. Her hands in rubber gloves within a chemical hood, she pours the undissolved rock residue into the tetrabromoethane. The lighter materials, floating, are removed. Inconveniently, conodonts are not all that sink. Pyrite, among other things, sinks, too. With methylene iodide, a fluid even heavier than tetrabromoethane, she turns the process around. In methylene iodide, the pyrite and whatnot go to the bottom, while the conodonts, among other things, float. Electromagnetically, she further concentrates the conodonts. She can now have a look at them under a microscope, seeing “bizarre shapes that any idiot can recognize,” and assign them variously to the Anisian, Ladinian, Cayugan, Osagean, Llandoverian, Ashgillian, or any other among tens of dozens of subdivisions of Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian, and Triassic time.
While recording ages, she could not ignore colors, and the question of their possible significance returned to her mind. In the Appalachians generally, formations thickened eastward. The farther east you went, the deeper the rock had once been buried—the greater the heat had once been. Heat appeared to her to have affected the color of the conodonts in the same manner that it affects the color of butter—turning it from yellow to light brown to darker brown to black-and-ruined smoking in the pan. Oh, she thought. You could use those things as thermometers. They might help in mapping metamorphic rock. The process by which heat and pressure change one kind of rock into another is divided into grades of intensity. Maybe conodont colors, plotted on a map, could demonstrate the shadings of the grades. At work, she began saying to people, “Show me a conodont and I’ll tell you where in the Appalachians it came from.” With amazing accuracy she repeatedly passed the test. She imagined that color had been controlled by carbon fixing. In the presence of heat, she thought, the amount of carbon in a given conodont would have remained constant while the amounts of hydrogen and oxygen declined, which is what happens in heated butter. No one seemed to agree with her. One way to test her idea might have been to scan for individual elements with an electron probe, but this was 1967 and electron probes in those days could not pick up light elements like hydrogen and oxygen. She sought other avenues of proof—with other types of equipment that no one has at home. The Geological Survey had a question for her, however. They said, “Who needs to know this anyway?” The Survey had been established to serve the public.
“O.K., to hell with it,” Anita told herself. Half a dozen years went by. With the oil embargo of 1973, the Survey felt a need to do everything possible to effect an increase in the nation’s energy resources. Its Branch of Oil & Gas Resources was expanded fifteen-fold. There were new positions for about two hundred front-rank geologists. They were hired away from oil companies or brought in from elsewhere in the Survey. What attracted the people from the companies was the opportunity to do publishable research. To run the branch, Peter R. Rose gave up his position as a staff geologist of Shell. Leonard Harris, of the Survey, a southern-Appalachian geologist whose interests had moved northward from the Ozarks, came into the Oil & Gas Branch, too. One day, he mentioned to Anita that he understood she was interested in conodonts. He said he would like to have some of her rock samples analyzed for “organic maturation.”
She listened to this dark-haired blue-eyed geologist as if he had come from a place a great deal more distant than the Ozarks. Just how did he propose to discern organic maturation? “Do you do that chemically?” she asked him.
“Yes,” he said. “You can. And you can also do it by observing changes in organic materials such as fossil pollen and spores, where they exist.”
“How do you do that?” she said.
“By looking at color change,” he said. “You see, the pollen and spores—”
“Stop!” she said. “Stop right there. They change from pale yellow to brown to black. Am I right?”
“Right,” he said. He was matter-of-fact in tone. He was, among other things, an oil geologist, while she was not. Oil companies had been using the colors of fossil pollen and fossil spores to help identify rock formations that had achieved the sorts of temperatures in which oil might form. Land-based plants, with their pollen and spores, had not developed on earth until a hundred and thirty million years after the beginning of the Paleozoic era, however. Nor would they ever be as plentiful and as nearly ubiquitous as marine fossils. Hearing Leonard Harris mention oil companies and their use of color alteration in pollen and spores, Anita realized in the instant that she had—in her words—“reinvented the wheel.” And then some. She had not known that pollen and spores were used as geothermometers in the oil business, and now that she knew it she could see at once that conodonts used for the same purpose would have different geographical applications, covering greater ranges of temperature and different segments of time.
“I think I can do the assessments easier and better by using conodonts,” she said to Harris. “Conodonts change color, too, and in the same way.”
It was his turn to be surprised. “How come I never heard about that?” he said.
She said, “Because no one knows it.”
Petroleum—the transmuted fossils of ocean algae—forms when the rock that holds the fossils becomes heated to the temperature of a cup of coffee and remains as warm or warmer for at least a million years. The minimal temperature is about fifty degrees Celsius. At lower temperatures, the algal remains will not turn into oil. At temperatures hotter than a hundred and fifty degrees, any oil or potential oil within the rock is destroyed. (“The stuff is there, throughout the Appalachians. You look at the rocks and you see all this dead oil.”) The narrow “petroleum window,” as it is called—between fifty degrees and a hundred and fifty degrees—is scarcely a fourteenth part of the full temperature variation of the crust of the earth, a fact that goes a long way toward explaining how the human race could have used up such a large part of the world’s petroleum in one century. Not only must the marine algae have been buried for adequate time at depths where temperatures hover in the window but once oil has formed it is subject to destruction underground if for one reason or another the temperature of its host rock rises.
Natural gas is to oil as politicians are to statesmen. Any organic material whatsoever will form natural gas, and will form it rapidly, at earth-surface temperatures and on up to many hundreds of degrees. In Anita’s words: “You get natural gas as soon as anything drops dead. For oil, the requisites are the organic material and the thermal window. When they look for oil, they don’t know what they’ve got until they drill a hole.” In trying to figure out where to drill, geologists have an obvious need for geothermometers. Pollen and spores are of considerable use, but only when they have fossilized in certain rocks. Moreover, they are absent altogether from early Paleozoic times, and they are extremely rare in rock from the deep sea.
Leonard Harris asked Anita how many years she had been “sitting on” her discovery about conodonts.
About ten, she told him. The last thing she had wished to do was to keep it secret, but no one had shown much interest. She gave him slides of the New York State east-west
series, and told him that a comparable set could be got together for Pennsylvania, too. Harris went south and traversed the state of Tennessee, collecting carbonate rocks that were close in age, and when Anita ran the conodonts she found the color alterations quite the same as in the northern states—dark in the east, pale in the west. Leonard and Anita reported all this to Peter Rose, leader of the Oil & Gas Branch, pointing out that the variations in conodont color could lead to a cheap and rapid technique of finding rock in the petroleum window. Rose said he couldn’t understand why no one in the United States had ever thought of this if it was as obvious as all that. Anita told him that for years she had been puzzled by the same question, since the procedure would be one that “any idiot ought to be able to follow, because all you need is to be not color-blind.”
At Rose’s request, Anita’s division of the Geological Survey allowed her to work two days a week on conodonts. Weekends, she worked on them at home. Actual temperature values had not been assigned to the varying colors. She did so in a year of experiments. She began with the palest of conodonts from Kentucky and heated them at varying temperatures until they became canary and golden and amber and chocolate and cordovan, black, and gray. With enough added heat, they would turn white and then clear. At nine hundred degrees Celsius, they disintegrated. By cooking her samples in a great many variations of the ratio of time to temperature, she was able to develop a method of extrapolating laboratory findings onto the scale of geologic time. She concluded that pale-yellow conodonts could remain at about fifty degrees indefinitely without changing color. If they were to remain at sixty to ninety degrees for a million years or more, they would be amber. The earth’s thermal gradient varies locally, but generally speaking the temperature of rock increases about one degree Celsius for each hundred feet of depth. A conodont would have to be lodged in rock buried three thousand to six thousand feet in order to experience temperatures of the sort that would turn it amber. At depths of nine thousand to fifteen thousand feet, she discovered, conodonts would turn light brown in roughly ten million years. If they spent ten million years at, say, eighteen thousand feet, they would be dark brown. In comparable amounts of time but at greater and greater depths, they would turn black, gray, opaque, white, clear as crystal. Anita also cooked conodonts in pressure bombs, because it had been suggested to her that the pressures of great tectonism—the big dynamic events in the crust, with mountains building and whole regions being kneaded like dough—might also affect conodont colors. Her experiments convinced her that pressure has little effect on color; heat is what primarily causes it to change.
