When John McPhee’s four-book geologic tour of the United States was collected in 1998 and published as the Annals of the Former World, McPhee was forced to confront a serious omission. McPhee’s geology tour ran along the 40th parallel, on route 80; the first two books covered America east of Chicago, and third and fourth, west of Nebraska. The Great Plains were tactfully omitted, because they had no geology to tour: tThe perfectly flat plains are perfectly flat because no rock intrudes to break up the monotony. The rock is there, it’s just buried, “tens and hundred and even thousands of feet down, but seldom does it outcrop, and, where it does, it is such an event that it is likely to have been named a state park.” But a coast to coast tour of the United States cannot skip Illinois, Iowa and Nebraska, and McPhee’s sense of duty compelled him to augment his four books with a fifth, Crossing the Craton. It tells the story of America’s deep rock basement, which underlies the waves of grain.
There’s interesting stuff down there, the North American craton: the continental nucleus, made up of precambrian rock—”precambrian” being the period which covers the first four billion of the Earth’s four-and-a-half billion year history. Precambrian rock is literally and metaphorically foundational. Nevertheless, says McPhee, Geological textbooks have generally given precambrian rock “one short chapter. First there was the basement, and on that grew the world.”
There are a couple of reasons for the dearth of precambrian scholarship. For one, old rock is constantly being melted, boiled and reformed as new rock. For another, there are no fossils in precambrian rock, because when precambrian rock formed, life hadn’t yet evolved anything fosslizable. An enormous amount of geological data is owed to oil companies, but very little of that data deals with the Great Plains or the great cratons. McPhee explains with “an expression oft heard in geology: ‘You could just about drink all the oil that ever came out of Iowa.'”
The rock chips that the oil companies pull up, being free of fossils, are somewhat hard to read. Every fossil has its place on the evolutionary timeline, and that timeline tells you how old a fossil’s surrounding rock is. But the geologists have a trick up their sleeves: Where they lack biological fossils, they substitute chemical fossils—the ratio of isotopes to one another, whose predictable rate of relative decay gives an accurate, if somewhat imprecise date of extremely ancient events in the Earth’s history. To a precambrian geologist, an imprecise date is a date that can’t be narrowed further than, say, a hundred million years. But since we’re talking about a time period that began five-hundred thousand millennia ago, which covers 40 distinct hundred-million year blocks, the precambrian geologist is frequently more precise than he gives himself credit for being.
And the data that the precambrian geologist has come up with is enough for McPhee to set a vivid scene of the Mars-esque pre-life Earth: “Precambrian landscapes had a barrenness beset by weather without vegetal control. The rock summits of high mountains would have looked like the summits of present time, the bare slops piled in fans of deep scree, like the ranges of Antarctica. Texture rested in topography, color in rock, braided rivers running over the rock. The cycle through which rock is torn apart, ground up, set down, stratified, and made into fresh new rock was unimpeded by so much as a root or stem, and therefore cycled more rapidly. Only gravity—with its angle of repose—held boulders and gravels to inclined ground. Silts and sands washed down quickly to lakes and seas. Unadorned, unembellished, severely simple, a picture of the precambrian would present to us the incongruity of a desert landscape invaded by white rivers drenched in rain.”
But evolution chugged on, and soon flora and fauna covered everything up. The great North American craton was covered by America’s bread basket, and the geologists were forced to its edges. This makes for a very short “Book Five” in McPhee’s five book set—it’s only 35 pages long, within a 700 page volume. Nonetheless, it’s a fascinating essay, and well worth a read.
All together, Annals of the Former World is the liveliest book ever written about geology, which is an axiomatically lifeless subject. Annals of the Former World won the Pulitzer in 1998; a richly deserved victory. Looking back at the Annals as a whole, however, I am compelled to say that book three, “Rising From The Plains,” stands head and shoulder above books one, two, four and five. In fact, it might be the best non-fiction I’ve ever read. If you end the centennial of America’s National Parks Service with one book about natural history, make that the one.
