The Rocks Don't Lie: A Geologist Investigates Noah's Flood (17 page)

Playfair also addressed Siberian mammoths. He noted that their bones were always found in soil or alluvial deposits and never in the solid rock below. Writing in the style of his time, he rambled on a bit before pointedly demolishing Kirwan’s conception of the Flood.

If we consider attentively the facts that respect the Siberian fossil bones, there will appear insurmountable objections to every theory that supposes them to be exotic, and to have been brought into their present situation from a distant country… . Shall we ascribe it to some immense torrent, which, sweeping across the desarts of Tartary, and the mountains of Altai, transported the productions of India to the plains of Siberia, and interred in the mud of the Lena animals that had fed on the banks of the Barampooter or the Ganges? Were all other objections of so extraordinary a supposition removed, the preservation of the hide and muscles of a dead animal, and the adhesion of the parts, while it was dragged for 2000 miles over some of the highest and most rugged mountains in the world, is too absurd to be for a moment admitted.
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Playfair further noted how their carcasses would surely have rotted if these great beasts had died in a tropical climate. Whatever they were, mammoths were not relics of the Flood.

By the close of the eighteenth century, theologians had begun to recognize the lack of a unified explanation among natural philosophers for Noah’s Flood and the age of the world. The wide range of conflicting theories and interpretations fostered suspicions that perhaps it was the Bible that was being misinterpreted. The floodgates of heaven and the fountains of the deep had been interpreted to refer to comets, a great vapor canopy, water from alpine caves, and a vast subterranean sea—just about everywhere one might imagine finding enough water to drown the world. Theologians started to question whether scripture was meant to be a source of scientific information as well as a book of personal and moral redemption. Even conservative Christians began to question whether Noah’s Flood was all there was to earth history.

It is impossible to stand at Siccar Point and reasonably see how to fit what you can read in the rocks into just 6,000 years of time. When Roman ruins still stand after 2,000 years, how could raising and eroding off two mountain ranges happen in just twice as long before that? The virtually unimaginable amount of time required to form the two unconformable sandstones exposed along the Scottish coast offers a humbling glimpse of the infinite.

Hutton’s recognition of the concept we now call deep time laid the foundation for a new geological time scale. It was a turning point in our story and a huge development for the field of geology. Reinterpreting the days of the week of Creation as geological ages allowed earth history to accommodate vast expanses of geologic time. After all, who knew how long one of God’s working days lasted? Perhaps the rock record paralleled Genesis—if interpreted as consisting of six ages rather than six days. Maybe Moses only wrote about the part of the Flood that Noah witnessed. Although biblical interpretations were being reconsidered, there was still general faith that the rocks filled in the real story.

Then, as now, conventional wisdom guided interpretation of discoveries to the extent it could. Scientific revolutions happen when conventional views can no longer bend under the weight of new findings. Natural philosophers were still looking to prove Noah’s Flood because they viewed the world through the filter of religion, not because they feared theological condemnation. Despite the evidence Hutton and company marshaled to frame the geological story, natural philosophers were reluctant to abandon the biblical story. Only later did science start to modify and seriously undermine faith in biblical truth. Even so, it had become clear there was more to earth history and fossils than simple deposition of sedimentary rocks from a single flood over the span of a single year.

Soon geologists would unearth compelling evidence for multiple catastrophes, each of which ended a distinct period of earth history. As nagging questions and alternative ideas began to reshape how Christians interpreted the story of Noah’s Flood, natural philosophers shifted gears in looking for geological evidence of it. The search for Noah’s Flood moved from rocks into the overlying deposits of unconsolidated sediments that lay scattered across Earth’s surface.

7

Catastrophic Revelations

B
EFORE THE EARLY NINETEENTH CENTURY
, natural philosophers paid little attention to deposits of loose gravel, sand, and boulders lying above solid rock. But northern Europe’s geological blanket of unconsolidated material became far more interesting once it was thought that the part of earth history that overlapped with human history was preserved in surficial sediments rather than in the solid rock below. It helped that geology arose as a science in countries that had been glaciated, where a regional cover of glacial deposits—gravel, sand, boulders, and mud—resembled what you might expect a big flood to leave behind. These surface deposits and topography, the form of the land itself, became the link between the modern world people knew and the former worlds preserved in the rocky depths of geological time.

I came to appreciate the potential for catastrophic rearrangement of surficial deposits in the Philippines. At the time, I was doing fieldwork in the Pasig-Potrero River, where one of my graduate students was studying changes after the catastrophic 1991 eruption blew the top off Mount Pinatubo and buried the surrounding countryside under hot pumice and ash. The whole landscape around the volcano changed, as river valleys filled in with sediment only to have great canyons cut back down hundreds of feet into the loose debris in just a couple of years. We saw the Passig-Potrero River as an ideal place to study how rivers behaved when supplied with as much sediment as they could carry.

On a beautiful tropical morning, we started out from Delta 5, an abandoned military checkpoint perched on a rock outcrop sticking up from the riverbank. We headed upstream, leaving the coastal plains to enter the volcanic upland. Walking up the riverbed, we surveyed it in three-hundred-foot sections. One person would stay behind, sighting through a tripod-mounted level, as another took our stadia rod—a giant collapsible ruler—out to the end of a long tape measure. Using the level to read off the elevation every few feet as we moved the stadia rod along the tape, we measured the elevation of the riverbed. Repeating the survey over a number of years gave us a record of how the river ate down into the volcanic debris as lahars—volcanic mudflows—surged downstream to bury villages and towns beneath a blanket of sediment.

Just before lunch we noticed that an ominous black cloud had settled in over the volcano several miles upstream. The river started rising as we kept surveying our way up through a tight canyon. When the flow got deep enough to start moving the riverbed, grapefruit-sized rocks rolled into our shins and we decided to break for lunch on a sand terrace five or six feet above the water level. About halfway through lunch we noticed the water rising even faster. As the river started lapping up onto our lunch-stop terrace, we retreated to the foot of the canyon walls and watched six-foot-high waves cascade down the river we had walked up all morning.

Map of the Philippines showing location of Mount Pinatubo and the Pasig-Potrero River draining off the volcano’s eastern flank.

Alarmed, we climbed up through narrow side channels that had cut down through the volcanic debris—the only other way out of the canyon. By the time we reached the top of the side canyon we could see our lunch spot, several hundred feet below, submerged beneath a roaring torrent of bouncing boulders. We perched for the afternoon, trapped on the ridgetop but enthralled by walls of water crashing down the canyon. Here in front of us was a graphic illustration of what had drawn me to geology in the first place: Earth’s appearance of being stable—of being solid as a rock—only held some of the time.

In the early nineteenth century, the conventional view was that grand catastrophes reshaped landscapes in a geologic jiffy. The idea that the slow pace of everyday change could shape and reshape the world was considered delusional fantasy. By the end of the century, geologists believed that everyday erosion was how the world worked, and grand catastrophes had become geologically taboo.

Scientific curiosity and religious conviction were not alone in pushing efforts to better understand regional geology. Just as demand for iron and coal drove advances in mining and mineralogy, construction of railroads and canals created a need to understand regional geology. As necessity and practical interest grew, schools in industrializing areas began to appoint professors of geology. Studying rocks could be more than just an inspired hobby for those with the time, means, and inclination to seek insight into nature’s inner workings. It could be a livelihood. As geologists began to work out the details of local and regional geology, they reassessed the role of Noah’s Flood in earth history.

In 1815, surveyor and canal builder William Smith worked out the structure of England’s layered rocks in compiling what is widely credited as the first regional geologic map. He carefully documented a consistent, well-ordered succession of rock types across England that was far too systematic to have formed during the chaos of a globe-wrecking deluge. Smith also showed that different layers of rock consistently held different fossils. Based on observations collected over years of field excursions, Smith’s carefully compiled map allowed him to accurately predict the type of rock and the fossils in it virtually anywhere in England. His obsession with perfecting his map bankrupted both himself and the idea that a single catastrophic flood deposited layered rocks. After he published his map, geologists no longer looked for Noah’s Flood in the rocks. Instead they looked for signs of a great flood in topography and surficial deposits.

Across the English Channel, Smith’s contemporary Georges Cuvier, the vertebrate paleontologist who had dismissed Scheuchzer’s flood victim and concluded that mammoths were extinct, was busy mapping the rocks in the countryside around Paris. He found a sequence of distinctively terrestrial rocks containing fossil quadrupeds that alternated with layers full of fossil seashells. He knew that a single flood could not produce a thick sequence of interlayered terrestrial and marine rocks. Clearly, the sea inundated the land not just once but time and time again. Further fieldwork in the Paris basin unearthed evidence for alternating periods of fresh and saltwater inundation that Cuvier interpreted as evidence for at least half a dozen great floods, each of which ended a geological era. Instead of Hutton’s grand engine of slow change, Cuvier’s 1813
Essay on the Theory of the Earth
concluded that each catastrophe recorded another transition in a long series of geological eras. Ever since, these two views of geologic change—slow and steady versus catastrophic—have framed competing theories for how the world is shaped.

The idea that a catastrophic biblical flood could have remodeled the European landscape was vividly reinforced in 1818, when the Getroz glacier dammed the river Dranse in Switzerland’s Val de Bagnes. Advancing like the glacier that dammed the Tsangpo in Tibet, the ice blocked the river and a lake holding eight hundred million cubic feet of water formed above the frozen impoundment. When a tunnel was cut through it to draw down the lake, the ice and debris dam failed, sending a wall of debris-charged water surging down the valley at more than thirty feet a second. The flood swept away landmarks as sand and mud filled the local church to the pulpit. Huge boulders lay strewn around the fresh deposits. As residents dug out from the mess, they discovered trees and houses swept away in the torrent. The event impressed natural philosophers with how catastrophes could blanket large areas under sediment. Here, perhaps, was an analog for the geological signature of really big floods. The deposit left by this modern catastrophe looked a lot like the blanket of sand, gravel, and mud that covered much of northern Europe.