Before this breakthrough:
The attempt to fill this void has a long acrimonious history of false starts and embarrassing mistakes. But to understand this saga, we first need to know about the nature of geologic time and the historical development of the geologic timescale.
The older, the Precambrian Eon, is much longer and extends from when the planet formed, about 4,550 million years (abbreviated "Ma" for mega anna) ago, to the appearance of fossils of hard-shelled animals such as lobsterlike trilobites and various kinds of mollusks about 550 Ma ago. This eon is composed of two "eras," the older Archean Era (from the Greek archaios, ancient) that spans the timefrom 4,500 to 2,500 Ma ago, and the younger Proterozoic Era ("the era of earlier life," from the Greek proteros, earlier, and zoe, life) that extends from 2,500 Ma ago to the close of the Precambrian.
The younger and shorter eon is the Phanerozoic ("the eon of visible life" from the Greek phaneros, visible or evident, and zoe). It encompasses the most recent Earth history, roughly 550 Ma, and is divided into three eras (from oldest to youngest: the Paleozoic, Mesozoic, and Cenozoic), each subdivided into shorter segments known as "geologic periods." The oldest such period of the Paleozoic Era (and, consequently, of the Phanerozoic Eon), spanning the time from about 550 to a little less than 500 Ma ago, is known as the Cambrian Period, named after Cambria, the Roman name for Wales, where rocks of this age (the Cambrian System of rocks) were first formally described. Until just a few decades ago, rocks underlying and thus older than those of the Cambrian System were universally regarded as lacking fossils. As far as anyone could tell, life of the Precambrian had left no trace.
During the early 1800s, rock strata of the Phanerozoic were first studied actively in northern Europe, mostly in Wales and England. For this reason, many of the Phanerozoic geologic periods and their systems of rocks are named after geographic areas or ancient peoples of what is now the United Kingdom. For instance the Ordovician and the Silurian, the two geologic periods sequentially younger than the Cambrian, are named in honor of the Ordovices and the Silures, two ancient Welsh tribes. The Devonian, the next youngest period of the Phanerozoic, is named for Devon, a county of southern England. And the Cretaceous, the geologic period famed for the extinction of the dinosaurs at its close 65 Ma ago, is named after the outcrops of dusty white-gray chalk (in Latin, cretaceus) that form the aptly named White Cliffs of Dover on the northern shore of the English Channel.
These geologic pioneers were forced to rely almost entirely on studies of beds that were exposed to view in naturally occurring rock outcroppings, exposures rare in the "green and verdant" British Isles, where bedrock is mostly hidden by plant cover. Soon, however--spurred by the Industrial Revolution--long, interlacing systems of canals, dug to connect port cities with centers of industry, brought to view extensive swaths of newly exposed rock strata. From this, one of the most straightforward and logical rules of geology soon became obvious: in any sequence of undeformed sedimentary rocks (those made up of sedimented debris, such as marine sandstones and siltstones), any layer higher in the sequence must be younger than--deposited after--those below it. Known as the Law of Superposition, this simple notion--younger above/older below--provides a powerful rule of thumb for determining the relative ages of geologic units.
Though it is a simple logical notion, the Law of Superposition has limitations. About 70% of the world's surface is covered by oceans, a setting where sands and silts slowly settle to produce the rock-forming sediment that coats the ocean floor. But these sands and silts are derived from the land masses, carried to the oceans by streams and rivers. This means that the rocks that make up the continents, the remaining 30% of the Earth's surface, are being weathered away and destroyed. Except in rare settings (for example, at the bottom of large inland lakes or in glaciated areas where rocky debris can be piled high by massive ice flows), the continental surface is a site of rock erosion, not of rock formation.
Rock weathering, coupled with the sporadic nature of sediment deposition, leaves a record full of gaps. Almost always, only a small fraction of the total time spanned by any given sequence of rocks is represented physically by the rocks that are actually preserved. Nowhere on the Earth is there a continuous rock sequence that preserves strata from all ages. Younger above/older below holds true (except where mountain building has turned rock units upside down), but because of the time gaps, exactly how much younger and how much older is hard to know.
The Earth's continents are like slowly moving pieces of a gigantic jigsaw puzzle. Consider in your mind's eye the outlines of the western coast of Africa and the eastern coast of South America. The two coastlines fit together (a match said to have been first noted in 1620 by English philosopher Francis Bacon): before the Atlantic Ocean was born, the two continents were actually joined as parts of a single, much larger supercontinental landmass called Gondwanaland. In the same way that a simmering pot of thick soup slowly churs as steam bubbles from its surface, the splitting apart and movement of such massive geologic plates is caused by heat escaping from the planet's interior through cracks in the Earth's crust. Because the rock masses are so immense, they move very slowly, on average only about3 centimeters per year. But their movement is not smooth. At their boundaries they often stick together for a time and then suddenly jerk apart in the earth-rupturing jolts we know as earthquakes.
As the rocks of continents and ocean basins collide, the jerkily surging continental masses ride up over the sediments of the ocean floor, eventually forcing the sediments to such depths that they are melted by the Earth's heat. In this molasseslike state they ooze back up through cracks and fissures in the crust and spew out at the surface as fiery lavas, giving rise to volcanic islands and ocean-rimming mountain chains like those that ring the Pacific Ocean from Fujiyama to the Aleutians and down the west coast of the Americas to the Andes. Large-scale continental movement, driven since the Earth's formation by heat escaping from its depths, has happened throughout geologic time. To us this movement is imperceptibly slow, but geologic timeis so unimaginably long that no ancient rocks have survived on the ocean floor. The oldest known deposits of the world's ocean basins are geologically young, barely 250 Ma in age.
So, ordinary geologic processes--erosion, nondeposition, and the movement of the massive plates that make up the Earth's crust--conspire to limit the usefulness of the Law of Superposition. Without question, younger above/older below works well in a local outcrop or within a limited geographic area. But because this notion provides no way to gauge the length of time gaps in the preserved rock record, it cannot tell how much younger or how much older the rocks may be.
As more and more rock strata were studied, it became clear that different groupings of fossil species are present in rocks of different ages. The fossils could be used to order the rocks from older to younger. For instance, though trilobites and dinosaurs are not present together in any single rock unit, if both occur in a sequence of rocks the trilobites are always in strata below those that entomb the dinosaurs. The trilobites are demonstrably older, the dinosaurs assuredly younger. And as the science progressed, many different species, both of trilobites and dinosaurs were discovered--some more ancient, others more recent--and among these, certain forms were always present within, and therefore diagnostic of, rock strata of a particular previously well-established age. Wherever species of this type (termed "index fossils") are encountered, they provide firm evidence of the age of the embedding rocks.
Using the Law of Superposition and the insights provided by the documented succession of fossils and fossil assemblages, many local geologic sequences were soon linked together to make up a composite geologic column that by the 1830s already revealed the basic outlines of Phanerozoic evolutionary history. Enough detail was known to show even the two best-known episodes of Phanerozoic extinction--the demise first of the trilobites, at the end of the Permian Period and the Paleozoic Era, and later of dinosaurs at the end of the Cretaceous and the Mesozoic.
Studies of this type continue into the present, and a composite geologic column, based on countless geologic sequences, has been established for the entire Phanerozoic worldwide. This triumph is the result of two full centuries of observation, logic, and sheer hard work.
To see this, imagine that all 4,500 Ma of geologic time were condensed into a single 24-hour day. Evidence from the Moon and Mars tells us that for the first few hours of this "day" of Earth's existence its surface would have been uninhabitable, blasted by an intermittent stream of huge, ocean-vaporizing meteorites. At about 4:00 a.m., life finally gained a foothold. The oldest fossils were entombed in their rocky graves at 5:30 a.m. Gaseous oxygen--pumped into the environment by early-evolving plantlike microbes (cyanobacteria) and then chemically joined with oceanic iron to form rusty sediments known as banded iron formations--accumulated slowly until about 2:00 in the afternoon. Simple, floating single-celled algae with cell nuclei and chromosomes soon appeared, but by 6:00 p.m. they were supplanted by more rapidly evolving sexual plankton. At about 8:30 in the evening, larger many-celled seaweeds entered the scene and a few minutes later so did early-evolving jellyfish and worms.
The Precambrian, the period from the formation of the planet to the rise of shelled animals, spans 21 hours of this 24-hour "geologic day." The remaining 3 hours are left for the familiar Phanerozoic evolutionary progression, the schoolbook history of life recounted in texts and classrooms throughout the world. We humans arose only a few tens of seconds before midnight.
It is easy to understand why we might have a shortsighted view of life's long history and of the relevance of the Precambrian. The Phanerozoic fossil record has been a subject of fruitful study for more than two full centuries, and its organisms are large, striking, even awe inspiring. That this most recent 15% of Earth history is the "Age of Evident Life" is more than just a handy moniker. But studies of the Precambrian--the "Age of Microscopic Life"--have just begun. And though our relatedness to life of the Phanerozoic is obvious to all, it seems hardly credible that our roots extend to primitive Precambrian microbes, lowly life forms almost too small to be seen!
Yet obvious or not, each one of us is part of an evolutionary chain that extends to the distant Precambrian past and links us by the most basic living processes to ancient, primordial microbes. Why do we breathe oxygen? Why are we dependent on plants for the food we eat? Why is each of us similar to, but not identical with, our parents, our sisters, our brothers? The answers to these and other fundamental questions lie in an understanding of the Precambrian seven-eighths of the evolutionary story. And like so many aspects of natural science, the beginnings of that understanding come from the mid-1800s and the thoughts and writings of the famous British naturalist, Charles Robert Darwin (1809-1882).
The history of the hunt for Precambrian fossils is a prime example. In 1859, in his epochal volume On the Origin of Species, Darwin first focused attention on the missing early fossil record and the problemit posed to his theory of evolution. As others took up the question--some in support of Darwin's views, others seeking to undermine them--the debate became contentious. Honest mistakes, unwarranted claims, promising finds, important discoveries were all made. But since there were few facts to go on, status and privilege played major roles in deciding whose view would win the day.
Of his newly minted theory, Darwin wrote:
There is another . . . difficulty, which is much more serious. I allude to the manner in which species belonging to several of the main divisions of the animal kingdom suddenly appear in the lowest known [Cambrian-age] fossiliferous rocks . . . If the theory [of evolution] be true, it is indisputable that before the lowest Cambrian stratum was deposited, long periods elapsed . . . and that during these vast periods, the world swarmed with living creatures . . . . [However], to the question why we do not find rich fossiliferous deposits belonging to these assumed earliest periods prior to the Cambrian system, I can give no satisfactory answer. The case at present must remain inexplicable; and may be truly urged as a valid argument against the views here entertained.Darwin's dilemma begged for solution. And though this classic problem was to remain unsolved--the case "seemingly inexplicable"--for more than 100 years, the intervening century was not without bold pronouncements, dashed dreams, and more than a little acid acrimony.
Dawson's kudos were many. He was the first president of the Royal Society of Canada (1882), president of the Geological Society of America (1895), and the only person to be elected president both of the American (1882) and British (1887) Associations for the Advancement of Science. In 1884, in his sixty-fourth year, he was knighted by Queen Victoria.
Sir John Dawson was well schooled, chiefly in Edinburgh, Scotland, where early in his career he became a protégé of Sir Charles Lyell, the most distinguished British geologist of the day (and a mentor and major influence also of Charles Darwin). Unlike Lyell, however, Dawson was an old-school Calvinist Christian and staunch antievolutionist who, following centuries-old European tradition, believed that the proper, indeed the only role of science was to discover and exemplify, and thereby glorify, the workings of God. To J. W. Dawson, the obedient son of devout Scottish Presbyterians, science was a religious quest.
In 1858, a year before publication of The Origin, a local collector brought a number of unusual rock specimens to Sir William E. Logan, director of the Geological Survey of Canada. The specimens were old--gathered in Precambrian, "Laurentian" limestones (now dated at about 1,100 Ma) exposed along the Ottawa River to the west of Montreal--and they were evidently unique: thinly and regularly green- and white-layered in a way quite different from rocks typical of the region. Though Logan was not a paleontologist, the alternating regular layers suggested to him that these structures might be fossils. Over the next half-dozen years, Logan himself collected more specimens from limestone beds near Ottawa and displayed them at various scientific conferences, most notably at meetings of the Geological Society of London. Spirited debate ensued, but few geologists were willing to accept these curiously layered rocks as remnants of life.
In 1864, however, Logan brought specimens to Dawson, who not only confirmed their biologic origin but identified them as fossilized shells of huge foraminiferal protozoans ("forams" for short)--giant, oversized versions of the tiny, many-chambered shells that form thick accumulations in modern oceans and, when turned to rock, make up massive limestones like those used to build the great pyramids of Egypt. Dawson soon became so convinced of their biologic origin that a year later, in 1865, he proposed a formal scientific name for this supposed giant foram, Eozoön Canadense, the "dawn animal of Canada."
To many, Dawson's interpretation seemed hardly credible. Not only were these objects hundreds of times larger than any foram known, they were also evidently vastly older than any other fossils and were said to be preserved in rocks subjected to intense heating and deformation (metamorphism), sites quite unlikely to harbor fossil shells. But Dawson's published description of Eozoön was convincing, and the foraminiferal identity he proposed was soon seconded by William B. Carpenter, the leading foram specialist of the day. And since Carpenter was a senior scientist at the British Museum [Natural History], his pronouncement from this center of scientific power carried special weight.
With his view thus certified, Dawson became the champion Eozoonist, principal spokesman on behalf of what he termed this "remarkable fossil . . . one of the brightest gems in the scientific crown of . . . Canada," a role he continued to play up to his death some 40 years later. Over the intervening decades, claims and counterclaims, charges and countercharges--many intemperate, some highly personal--appeared in the public literature, most prominently as letters to theeditor of Nature (today arguably the foremost science journal in the world but at that time a fledgling British periodical).
The first shot of the anti-Eozoonists was fired in 1866 by two Irish geologists--William King, an expert on Permian fossil animals, and Thomas H. Rowney, a noted mineralogist--who argued that they could find none of the traces of organic structure Dawson and Carpenter professed to see, and therefore regarded Eozoön as a purely mineralic, nonbiologic structure. Led by Dawson, the Eozoonist camp vehemently rebutted: King and Rowney hadn't seen the "best" specimens; they obviously had written in haste; and, in any case, as neither foram specialists nor biologists they lacked the expertise to back their claim.
As the debate wore on, others joined the fray. In 1879, Karl Möbius, professor of zoology at the University of Kiel and the foremost foram expert in Germany, published a lengthy article in Nature that to many seemed to doom the Dawson-Carpenter claim. After studying some 90 sliced specimens of Eozoön, Möbius, like King and Rowney, was unable to detect telltale features of forams. He, too, was firmly convinced of its nonbiologic origin. By this time, Carpenter had withdrawn from the brawl, and though the anti-Eozoonists had gained the upper hand, Dawson was not to be dissuaded. He responded vigorously and at length (albeit with disdain and a degree of obfuscation).
Finally, in 1894, three full decades after Dawson had first seen specimens of this contentious "fossil," its claimed biologic origin was put to rest. J. W. Gregory and Hugh Johnston-Lavis discovered Eozoön in ejected blocks of limestone near Mt. Vesuvius in Italy and showed they were geologically young, formed by heat and pressure on limestone. No one, not even Dawson's steadfast supporters, could accept the notion of a "Precambrian fossil" shot out of a modern volcano!
The doubters had been right from the beginning. Dawson's famous and now infamous "dawn animal" was nothing more than a curiously layered mineral deposit formed when hot molten rocks intruded into Laurentian limestones, deforming and altering them to produce thin intermittent layers of a green-colored metamorphic mineral known as serpentine. Yet despite the overwhelming evidence, Dawson continued to press his case for the rest of his life. Over four decades, as a steady stream of evidence had mounted against him, he never admitted defeat.
Why had Dawson struggled on? In part because of hubris--dogged self-assurance. By all accounts, Dawson was a prideful man and, as the acknowledged expert on Canadian geology, his reputation was at stake. Moreover, he was pugnacious. The Eozoön controversy was just one of a number of contentious scientific issues in which he was a vocal participant. But Dawson's main spur appears to have been his strict Calvinist faith and unquestioning belief in biblical truth. Were he to have proved the biologic origin of Eozoön he would have succeeded in exposing the greatest missing link in the entire fossil record, opening a gap so enormous he thought it would certainly undermine Darwin's theory by showing that evolution's claimed continuity was a myth, leaving biblical creation as the only answer. Dawson's view is well expressed in his book The Dawn of Life, written in 1875 when the debate was hot and heavy: "There is no link whatever in geological fact to connect Eozoön with the Mollusks, Radiates, or Crustaceans of the succeeding [rock record] . . . these stand before us as distinct creations. [A] gap . . . yawns in our imperfect geological record. Of actual facts [with which to fill this gap], therefore, we have none; and those evolutionists who have regarded the dawn-animal as an evidence in their favour, have been obliged to have recourse to supposition and assumption."
It is interesting--and ironic--that in the fourth and all later editions of The Origin Darwin cited the Precambrian age and primitive protozoal relations of Eozoön as consistent with his theory of evolution. This was just the sort of "supposition and assumption" that Dawson found so distressing.
Darwin was right in raising the question of the missing Precambrian fossil record. But he and Dawson were both mistaken in thinking that the "dawn animal of Canada" had bearing on the issue.
Like Dawson before him, Walcott was enormously influential and highly honored. Except for repeated forays into the field to do geology, he spent most of his adult life in Washington, D.C., where he served as the CEO of three of the most prominent of all scientific organizations--first, as director of the United States Geological Survey (1894-1907), then as secretary of the Smithsonian Institution (1907-1927) and president of the National Academy of Sciences (1917-1923). Though his administrative responsibilities were heavy, he also found time to fit in terms as president both of the American Philosophical Society and, like Dawson, the American Association for the Advancement of Science.
Walcott was remarkably well connected. Appointed director of the U.S. Geological Survey by no less than President Grover Cleveland, he was well acquainted with Presidents McKinley, Taft, Harding, and Coolidge, a confidant of Presidents Theodore Roosevelt and Woodrow Wilson, and a close friend of captains of industry AndrewCarnegie and John D. Rockefeller. These contacts paid dividends to Walcott personally and to the organizations he headed as well as the country as a whole, for it was C. D. Walcott who influenced McKinley to set aside national forest reserves and who laid the groundwork with President Roosevelt for establishment of the U.S. National Park Service.
Surprisingly, however, Walcott had little formal education. As a youth in northern New York State he received but 10 years of schooling, first in public schools and, later, at Utica Academy (from which he did not graduate). He never attended college and had no formally earned advanced degrees (a deficiency for which he more than compensated in later life when he was awarded honorary doctorates by a dozen academic institutions).
In 1876, as a 26-year-old budding geologist and avid fossil collector, Walcott was hired as assistant to James Hall, chief geologist of the state of New York. This was a stupendous opportunity--Hallwas the acknowledged dean of American paleontology, famous also in geologic lore as an "irascible tyrant" of "unbridled temper." Two years later, Walcott took a 2-week vacation to the town of Saratoga in eastern New York State to examine Cambrian limestone beds packed with distinctively layered, mound-shaped structures that Hall had discovered there a few years earlier. The more or less cabbagelike structures were just as Hall had described--irregularly shaped, large cannonball-like masses, up to a meter across and circular to oblong in cross section, made up of thin, undulating layers of dark- and light-colored limestone. Ever the astute observer, Hall believed the structures to have a decidedly "biologic look," and though he was never able to find direct evidence (such as preserved cells) of the organisms that constructed them, in 1883 he formally named them Cryptozoon (from the Greek meaning "hidden life") and interpreted them as reefs laid down by flourishing communities of microscopic algae. After a firsthand look at the specimens, Walcott too was convinced of their algal origin, an opinion that in later years was the foundation for his side of what came to be a rather nasty argument known as the"Cryptozoon controversy" (which we'll encounter again later in this chapter).
In the spring of 1879, the U.S. Geological Survey was established by an act of Congress. In July of that year, at the recommendation of James Hall, Walcott was appointed (officially, USGS employee no. 20) as an assistant geologist, the lowest rung on the Survey's ladder, receiving an annual salary of six hundred dollars. Immediately upon taking the oath of office he was assigned by survey director John Wesley Powell to an expedition heading to the vast, geologically little known Grand Canyon region of the western United States. Over the next several field seasons, Walcott and his comrades--geologists, naturalists, explorers, mappers, hunters--charted the geology of sizable segments of Arizona, Utah, and Nevada.
Director Powell, who had earlier led the first perilous expeditions into the depths of the Grand Canyon, had a hunch that Precambrian rocks there might contain evidence of ancient life. He assigned Walcott to assess the possibility. Powell's hunch bore fruit when, in 1883, Walcott reported he had found Precambrian specimens similar to Cryptozoon. This was a promising beginning, and over the next several years Walcott became convinced that his search for Precambrian fossils would eventually prove even more fruitful. In his words, from an article of 1891: "That the life in the [Precambrian] seas was large and varied there can be little, if any, doubt. . . . It is only a question of search and favorable conditions to discover it."
By 1899 Walcott's perseverance paid off with a startling find--fossils he thought were remnants of early animals: small, millimeter-sized black coaly disks found in Precambrian carbon-rich shales on the slopes of a prominent butte deep within the Grand Canyon. The shales belonged to what is known as the Chuar Group of strata so, Walcott named the fossils Chuaria. The specimens were flattened, compressed between thin shale beds, and because Walcott (like Darwin before him) assumed that Precambrian rocks would yield the same sorts of fossils found in strata of the overlying Phanerozoic, he interpreted the disks as "the remains of . . . compressed conical shell[s]," possibly of marine invertebrate animals known as lampshells (brachiopods). In this he was mistaken. Rather than a small flattened shell, Chuaria is now known to be an unusually large, originally spheroidal, single-celled planktonic alga (technically, a "megasphaeromorph acritarch"). Nevertheless, Walcott's specimens were indeed authentic fossils, the first true cellularly preserved Precambrian organisms ever recorded.
After the turn of the century, Walcott moved his fieldwork northward along the spine of the Rocky Mountains, focusing first in the Lewis Range of northwestern Montana (an area since set aside as Glacier National Park) and then high in the Canadian Rockies at the eastern border of British Columbia in what is now Yoho National Park. From the Precambrian of Montana he reported many types of Cryptozoon-like structures (technically, "stromatolites"), all interpreted as built by "algae" (microorganisms today classed as cyanobacteria), to which he gave formal scientific names. And, in 1914 and again in 1915, he reported finding in these same rocks minute cells and chains of cell-like bodies he identified as fossil bacteria.
His studies in the Canadian Rockies, from 1907 to 1925, were even more rewarding. In 1909, near Burgess Pass at an elevation of 8,000 feet and close to the present-day tourist centers of Banff and Lake Louise, Walcott discovered a diverse marine flora and fauna that were amazingly well preserved in strata of Cambrian age, which he named the Burgess Shale. Between 1910 and 1917, when he was well into his sixties, he set up a quarry at the site and extracted literally tons of fossiliferous rock that he shipped to his Smithsonian laboratory for study.
Over the years, the remarkable fossils of the Burgess Shale have come to be increasingly famous, known to interested scientists and nonspecialists alike, as chronicled, for example, in Stephen Jay Gould's 1989 best-seller Wonderful Life and featured even on a December 1995 cover of Time magazine. Though many of Walcott's initial interpretations were later revised as other workers discovered new, astonishingly strange Burgess organisms (one especially bizarre and aptly dubbed Hallucigenia), his benchmark find has continued to provide the finest and most complete sample of Cambrian life known to science.
Walcott's contributions are legendary. He was the first discoverer in Precambrian rocks of Cryptozoon and other cyanobacterium-built stromatolites, of cellularly preserved algal plankton (Chuaria), and of possible fossil bacteria, all capped by his pioneering investigations of the world-famous fossils of the Burgess Shale! The acknowledged founder of Precambrian paleobiology (as the science has since come to be known), Walcott was the first to show, nearly a century ago and contrary to accepted wisdom, that a substantial fossil record of Precambrian life actually exists.
Charles Doolittle Walcott had brought Precambrian paleobiology to the brink of success. In one deft stroke, in a single influential textbook of 1931, Albert Charles Seward (1863-1941) snatched defeat from the jaws of this impending victory. "Seward's Folly" (that of A. C., not William Henry who bought Alaska for the United States from Russia in 1867) set the field into a tailspin of confusion that lasted for more than three decades.
A. C. Seward was a man of intelligence and influence, many accomplishments, and a large number of titles. Associated throughout his career with the University of Cambridge, England, he served as professor of botany; master of Downing College; honorary fellow of Emmanuel, St. John's, and Downing Colleges; and, in 1924-25, as vice-chancellor of the university. He was a fellow both of the Linnean Society (where Darwin's theory of evolution was first presented in 1858) and the Geological Society of London (where the biologic origin of Eozoön was hotly debated in the 1860s), and, like Sir J. William Dawson, he served as president of the British Association for the Advancement of Science. In addition to an earned Ph.D. degree he was recipient repeatedly of honorary Sc.D., D.Sc., and LL.D. degrees. As a fellow (and, from 1934 to 1940, as vice-president) of the prestigious Royal Society, he appended "F.R.S." to his signature, and, like Dawson, he was knighted (in 1936) by the British monarch.
Sir A. C. Seward was the most widely known and influential paleobotanist of his generation. He authored nearly a dozen paleobotanical textbooks, and because practially all claimed Precambrian fossils fell within the purview of paleobotany--whether presumed to be algal, like Cryptozoon, or even bacterial--Seward's opinion had enormous impact.
In 1931, in Plant Life through the Ages, the standard paleobotanical text then used throughout the world, Seward assessed the "algal" (that is, cyanobacterial) origin of Cryptozoon as follows:
The general belief among American geologists and several European authors in the organic origin of Cryptozoon is, I venture to think, not justified by the facts. . . . [Such forms] are precisely the same in their series of concentric shells as many concretions which are universally assigned to purely inorganic agencies. . . . It is clearly impossible to maintain that all such concentrically constructed bodies are even in part attributable to algal activity. . . .Seward was even more categorical in his rejection of Walcott's report of fossil bacteria:[Cyanobacteria] or similar primitive algae may have flourished in Pre-Cambrian seas and inland lakes; but to regard these hypothetical plants as the creators of reefs of Cryptozoon and allied structures is to make a demand upon imagination inconsistent with Wordsworth's definition of that quality as "reason in its most exalted mood."
In a very few examples [of Cryptozoon-like structures] the residue left after treating the rock with acid revealed the presence of a small number of cell-like structures, the organic nature of which cannot be said to have been established. . . . It is claimed that sections of a Pre-Cambrian limestone from Montana show minute bodies similar in form and size to cells and cell-chains of existing [bacteria]. . . . These and similar contributions . . . are by no means convincing. . . . We can hardly expect to find in Pre-Cambrian rocks any actual proof of the existence of bacteria.An entertaining writer whose texts are spiced with scholarly quotes and poetic couplets, Seward closed his discussion with the following:
My desire is to lay stress on the need of a more critical examination of the evidence which has led to the description of the earliest phase of geological history as an "Age of Algae"--algae with doubtful credentials:Seward was partly correct. Mistakes had been made. Mineralic, purely inorganic objects had been misinterpreted as fossil. Better and more evidence, carefully gathered and dispassionately considered, was much needed."Creatures borrowed and again conveyed, From book to book--the shadows of a shade."
But, overall, Seward was in error. His aggressive skepticism, delivered from his throne of unquestioned authority, was a disservice to the field. Seward's positive contributions were many (for he truly was a leader in the development of paleobotanical science), but his assertive disbelief of the biologic origin of Cryptozoon and his dogmatic pronouncement that "we can hardly expect to find in Pre-Cambrian rocks any actual proof of the existence of bacteria" stifled the hunt for the missing Precambrian fossil record for nearly 40 years.