Grandeur in the saga of the rocks

Since that date in the late 1960s when the Apollo project broadcast the first stunning blue and white photograph of the sphere of the earth from space, our relation with our planet has been transformed. Before this event made us learn to face earth as the cool and beautiful being it is - our pale dot in the endless black speckled with stars - the world was simply a complicated place. It was a source of water and land to grow food plants, a motley collection of lands quarrelled over by dissatisfied peoples, each with claims to territory, and fishable seas with a somewhat superior history, to which the planet was a mere backdrop. Expanding and shrinking ice-caps, mountain building, earthquakes, hurricanes, landslides and desertification were all seen as processes of the planet's surface determined by physical laws. The professional geologist, whose object of study is the earth, in pre-Apollo days found himself employed in researching those laws and advising citizens accordingly. The land and sea were seen as an immense stage for the human theatre, providing an exploitable background to power struggles over mineral rights and coastal resources. The planet's covering of organisms was regarded as a peculiar set of live and formerly live passengers on an amusement park ride, with plants and animals and man the driver attached by gravity to a huge rock, Spaceship Earth, going round and round the sun in circular orbit.

Not any more. Prior to the now-cliched Nasa image from Apollo, it occurred to no one that the entire planet was alive. Today, writes Richard Fortey, we think of the early earth of 4,000 to 1,500 million years ago as "growing into an interconnected web of life, chemistry, oceans and geology - even the most sceptical reader will be able to accept that this much of (James) Lovelock's Gaia hypothesis must be true. Life made the surface of the earth what it is, even while it was earth's tenant." Nasa's photo showed us the mobile facial expressions of the planet. Eureka! This giant blue marble is at once both a body, of which we people are a part, and a home. Seeing the earth rise from a vantage point on the moon made millions of us realise that since earth is alive it must have a personal history. For Fortey, the totality of earth-bound life is a subject ripe for biographical inquiry. The fact that his fascinating biography is "unauthorised" is clearly a major aspect of its charm. If it had been authorised, the book would presumably have read like any historical geology text and all the spunk would have been purged.

The order of the book is chronological beginning with life's first appearance. The endpapers show tens of metres of neatly layered and undisturbed sediment over which the reference scale of 4,000 million years of geological time from the Archean at the bottom to the Holocene at the top, is handily superimposed. (Unfortunately, since we are not given the location or composition of the sediments, their age or their range in years, the diagram is more decorative than useful.) In its 13 chapters, illustrated with 88 plates of black and white photographs, microbes originate, plants come ashore and animals, including early human apes, appear, evolve and die out. The book ends with the statement that "Life will probably cope."

My main misgiving is the extent of Fortey's biological misunderstandings. No longer is plant all that is not animal: much of the Ediacara biota, hardly a "fauna", is protoctist. Fortey, unclear about just what animals, plants, fungi, protoctists and bacteria are, fails to tell us when they first appear in the record. So too is he unaware that cyanobacterial atmospheric oxygen comes entirely from water (from which the hydrogen atoms are greedily extracted) and not at all from the oxygen in the air's carbon dioxide. Atmospheric carbon dioxide is used to make cell material by cyanobacteria, bacteria that live in sulphur and methane environments, and by other bacteria which Fortey mentions.

But we more than forgive the author because of his lively language and personal narrative. He is both extraordinarily well read and impressively international. He leads us in a dance through time that is enthralling; we begin to know personally the trilobite-ridden Cambrian sea flooding over Australia. "Trilobites are my family," he writes, "they probably adopted me long before I went to Spitzbergen, when, as a lad armed with optimism and a coal hammer, I tapped along Welsh cliffs and riverbanks in their pursuit." We meet Ordovician nautiloids through the smoke-filled eyes of the author's room-mate, the quintessential eccentric Rousseau H. Flower. From his youthful field trip in the severe landscape of Spitzbergen to his recent forays into the world of cladistics, Fortey is highly specific about people and places all over the world. He seems to have been everywhere and met everyone actively participating in the palaeontological search to reconstruct the history of life on earth: Dolf Seilacher, Stephen J. Gould, Chris Stringer, Bob Bakker and all sorts of other hard-working palaeontologists step in and out of these pages. He is even on first-name terms with luminaries now dead such as the three Charleses: Lyell, Darwin and... Lapworth.

Many of the scientists, localities and rock formations mentioned are familiar to geological enthusiasts who, like me, will turn to this book again and again for its richness of detail. Its breadth and readability are complemented by the cohesiveness of its narrative, a happy characteristic lacking in nearly all current scientific writing. Many examples could be chosen to illustrate the grandeur of Fortey's saga of the rocks but space permits me to review only one: Lapworth's half-a-billion-year-old marine shales.

Who was this Charles, and why does he deserve to be listed in such illustrious company? Lapworth was a practical and artistic geologist, who began as a school teacher and ended his career as a professor at Birmingham. He gave the name Ordovician, after the Ordovices, a Welsh hill tribe at the time of the Roman empire, to a geological period in the Lower Palaeozoic, "the meat in the sandwich between Cambrian and Silurian" (to quote Fortey). In his famous 1879 compromise between Sedgwick's Cambrian and Murchison's Silurian claims, Lapworth assigned the older Welsh rocks to the Cambrian and the younger to the Silurian while carving out a new time period in the middle, now taken to run from 505 until 438 million years ago.

Fortey is "deeply fond of this Ordovician country, for all its concealed bogs and incomprehensible gates". He notes that in a few places (Snowdon, Cader Idris) where Ordovician rocks are "reinforced by flows of lava and pumice which once erupted angrily over a sea swarming with brachiopods, trilobites and conodont animals, over which lazy graptolites drifted in their incessant trawl for plankton", they make mountains.

Lapworth's Ordovician was the "age of graptolites". The name of these fossils (from Greek: graptos, "marked with letters", + lite, "stone") aptly describes their sawtooth indentations that look more like ancient petroglyphs than animal body fossils. Graptolites formed a colony of tiny organic tubes; a millimetre-long series might contain 100 tubes. Only very recently has the modern encrusting hemichordate (Rhabdopleura) been comprehended as a humble descendant of the great evolutionary flowering of Ordovician graptolites.

Neither Lapworth, nor anyone else until recently, understood much about the relation of graptolite fossils to living organisms, although of course he recognised their usefulness in deciphering the age and environment of deposition of the rocks in which they appeared. In 1878 Lapworth succinctly summed them up as an illustration of the "older-at-the-bottom law" when he wrote that each "species and variety of graptolite has a definite range in the vertical succession of strata". These colonies of tube dwellers dominated the ancient seas with an abundance and diversity not exceeded by any of today's plankton-eating animals. Since graptolites of all kinds at the surface and in the depths of the sea harvested microscopic plankton in the absence of any company, some Ordovician sedimentary rocks are crammed with their lonely remains.

The wild tract of land, called the Southern Uplands, running from east to west across the south of Scotland, was once a calm Ordovician sea full of tangled feeding colonies of graptolites before it was disturbed in the Caledonian mountain building episode. The original sea-bottom's sedimentary rocks mark the ancient Ordovician world just as oceans began to become modern: sea urchins and starfish appear, the reefs acquire corals, large predatory coiled and straight shelled nautiloids abound, clams have learnt to burrow, sea lilies (crinoids) wave in the underwater currents. Some predators were unlike any before or since, sea scorpion monsters. Slimonia, a two-metre-long aggressor, on exhibit more than 400 million years later at the Natural History Museum in London, lay motionless for hours, if not days, before presumably lunging to poison its prey. Such sea scorpions, not sharks, were king in the Ordovician ocean.

Their monarchy collapsed when a great, if protracted event banished forever the thriving Ordovician seascape. Such a massive, worldwide tragedy for open-ocean graptolites and their coastal temperate and tropical relatives, was of a kind which happens, according to Fortey, "every couple of hundred million years". Ice ages came again to the earth. The Ordovician marine habitat, once like that off Sydney harbour, Cornwall's rocky peninsula or Massachusetts's Elizabeth Islands including Nantucket and Martha's Vineyard, was transformed into blocks of kilometre-high ice. Of the many kinds of Ordovician graptolites documented by Lapworth only one or two kinds survived. These gave rise to all the subsequent Silurian species until all the graptolites were extinguished at the end of the Palaeozoic.

Fortey claims that "the world is forever in the grip of mutability" in his enlightening discussions of periodic ice ages that marked not only the Ordovician but the Carboniferous, Permian, Miocene and most likely the Recent as well. Throughout geological time, the rocks tell us, the lush green continents we know today, with their shelves, slopes and offshore depths, have been frozen, scoured and desertified by enormous, inexorably expanding, rocky glacial ice masses.

How do we know for sure? On what evidence does this palaeo-interpreter base his conclusions? Who has the audacity to claim that 438 million years ago the Ordovician seascape became icy and barren, never to recover its life? With extraordinary skill in describing his field experience, Fortey, at his best, captures the suffering at the end of the Ordovician world. Suffice it to say that the author reads the landscape in Canada, Norway, Switzerland, Wisconsin, Spitzbergen, Greenland, Australia, the anti-Atlas mountains of Morocco as part of the reconstruction of history from clues he takes to be representational.

Most pertinent is his description of the relentlessly sun-beaten sands of the Arabian peninsula at Oman. Fortey tells of a huge valley scored by great deepening grooves, of rock gouges and scratches that looked as if they had been "scraped by the fingernails of some Titan clawing the ground in rage". He convinces us that polished rock, deep scratches and unsorted boulders on the valley walls were only some of the remarkable remnants of the huge ice blocks that used to occupy today's burning valleys of Oman. He leads us to see the unmistakable clues of advancing ice sheets that stop for no one. We realise the unity of the single ancient earth system as he reconstructs for us the massive ice blanket, once contiguous, on Africa, South America, India, the Arabian peninsula, Antarctica and Australia. Moving down from the shifted south pole our mind's eye sees the huge Permian impertinence of perpetual ice on a planet-wide continental mass. We discover, that is, not today's Gaia but the ancient world's Pan-geae.

The earth's surface has suffered a long-term chill that left its record in the rocks so many times in the past. The geological facts summarised by Fortey make clear that all of us are embedded in this single continuous story of the earth's surface. The belief that we are independent from the planet is an ingenuous and dangerous political delusion. Even if you reject this idea, I strongly recommend you to read at least this book about the living earth's body and newly envisaged face.

Lynn Margulis is professor in the department of geosciences, University of Massachusetts, Amherst, United States.