Kitabı oku: «Too Big to Walk», sayfa 3
The public hath of late been agreeably entertained with description of many curious Fossils, discovered in different parts of this kingdom; but very little hath been offered with a view to ascertain their origin and formation; a point of much greater importance to a curious mind, than the most accurate descriptions, or the neatest delineations.
This was a key point: describing fossils was all very well, and drawing them, though intrinsically useful, did not reveal what they actually were. For his paper, Platt broke open the belemnites and neatly described what he found within. This was a pioneering attempt to explore the anatomy of fossils, a discipline that became a mainstay of palæontology in the centuries that followed.29
Another important discovery was made in England in 1766 when an ichthyosaur jaw bearing teeth was discovered in strata at Weston, near Bath. It was exhibited as the bones of a crocodile by the Society for Promoting Natural History in 1783; meanwhile, more ichthyosaur fossils were included in the plates for a book by John Walcott published in 1779.30
The huge skull of a mosasaur was excavated in St. Pietersberg, near Maastricht in the Netherlands, and was later given the name of Mosasaurus hoffmanni. This fanciful portrayal of the event was engraved in 1799 by G.R. Levillaire.
It was in 1764 that European scholars first encountered a dinosaur skull, though nobody realized its significance. This specimen had been dug out of a chalk mine by quarrymen at St Pietersberg, near Maastricht in the Netherlands, and took the form of fragments of jaws with rows of fearsome teeth which were assumed to be the remains of a crocodile. Two years later it was purchased from the miners as a curiosity by Lieutenant Jean Baptiste Drouin; Martinus van Marum, who had opened the Teylers Museum in Haarlem in 1784, subsequently acquired it as a highlight of the museum’s displays, and in 1790 he published a description of it as ‘a large fish skull’.31
Pieter Harting published this engraving as the ‘Jaws of the Mosasaur’ in his book Album der Natuur in 1866. The original fossil was captured by the French in 1795 and taken to the Muséum National d’Histoire Naturelle in Paris, where it may still be found.
A second, similar, skull was excavated a few years later, on nearby land owned by Canon Theodorus Joannes Godding. He displayed it in his home as a curiosity until it was seen by a retired army doctor, Johann Leonard Hoffmann. Hoffmann was a keen fossil collector and decided this must be the skull of a crocodile. A friend of Hoffmann’s was the collector Drouin, and together they concurred that the remains were again those of a crocodile – or possibly a whale. French revolutionary forces under Napoleon occupied Maastricht in 1794, and this fossil was traded for 600 bottles of wine and taken as a trophy straight to Paris. Philosophers conventionally interpreted these petrified remains as coming from familiar creatures, and fossils were widely discussed by learned naturalists. Nobody imagined that fossils might be the remains of long-forgotten creatures, unknown to present-day scholarship, which had roamed the Earth in prehistoric times. It was assumed that the world then was much the same as the world of the past, though there was growing evidence that the Earth had changed over time. As long ago as 300 BC Aristotle’s young protégé Theophrastus had written a work entitled Peri Lithon (‘concerning stones’), which is the earliest work we know of that dealt with rocks. Theophrastus also noted that the draining of coastal swamps had rendered an entire area prone to freezing. He was also a pioneer of climate change, calculating that forest clearance resulted in warmer weather, because more heat could now reach the ground.32
The novel notion that the Earth could change over time was slowly emerging. A United Nations report quotes Vitruvius from around 50 BC, who recorded that many ancient settlements along the Anatolian peninsula in the Aegean Sea had been engulfed when changes in the landscape caused the sea to encroach. This is the first known record of major changes in the Earth’s surface. We now know that there are many ancient cities at the bottom of the sea – one in the Bay of Cambay, India, dates back 10,000 years, and there is another vast city on the bed of the Yucatán Channel near Cuba.33
Georges Cuvier published this refined engraving as ‘The Mosasaurus of Maastricht, Huge skull found in a quarry at Fort St Peter near Maastricht, Netherlands, in 1780’ in his book The Animal Kingdom published in London by Whitaker & Co, 1830.
Another idea that was slowly emerging was that the prehistoric climate had also changed over time. The evidence first emerged from the remote villages of Switzerland, where the local people used to say that the gigantic boulders they found scattered along the valleys were signs that glaciers had once extended further down from the mountains. Pierre Martel, an engineer from Geneva, visited these villages in 1742 and later wrote about these stories. Perhaps the landscape and the climate had once been very different. At the time, this was an unpalatable prospect.34
At about the same time, a Swedish mining engineer, Daniel Tilas, was studying the erratic boulders in many of the Scandinavian countries and the nations bordering the Baltic Sea, and he similarly speculated that they were brought to their present positions by glaciers that had existed in the past.35
Matters were about to change with the revolutionary ideas of James Hutton, a Scottish farmer turned naturalist. Hutton had lectured on the structure of the Earth, and in 1785 he presented his findings in a lecture to the Royal Society of Edinburgh. He argued that many rocks were not original, primeval structures, but had been modified and subject to sedimentation and later to weathering. Hutton introduced a basic principle of modern geology, somewhat clumsily termed uniformitarianism, which states that the natural forces that we see operating on the landscape today are essentially the same as those operated in past æons. He concluded that the movement of rocks by prehistoric glaciers, like the progressive erosion of the coast, was the cause of the landscape around us. Geology was suddenly seen as relevant to the study of the present-day Earth.
A replica of the original fossil from which the previous illustration was taken is on display in the Natural History Museum, London. The original specimen remains for the time being in the Muséum National d’Histoire Naturelle in Paris.
The term ‘geology’ had first been used by Ulisse Aldrovandi in his will of 1603, and came from the Greek γῆ (gē, earth) and λoγία (logia, study). Not until Hutton, however, was the subject given proper scrutiny and set on a firm scientific footing. Hutton used his principle of uniformitarianism to argue that many of the features of the present-day rocky landscape had begun at the bottom of the oceans, that many forms of rock had been produced by collections of ‘loose or incoherent materials’, and that these rocky layers were subject to rising, or falling, over the passage of immense periods of time. This was the first time anyone had put together the ideas fundamental to geology. In 1795, he finally published a book on his conclusions, and the new science of geology was firmly established.36
Several years after Hutton’s work, a Swiss hunter, Jean-Pierre Perraudin, decided to look further into the massive granite boulders that lay scattered around his home in the Alpine village of Lourtier. Perraudin was a professional hunter of chamois, the pretty mountain goats from which the finest leather is obtained. As he hiked across the mountains, he noticed two key facts: not only were there massive granite rocks scattered across the valley floor, but they were very different from the rocks nearby. They didn’t belong there. Secondly, he kept coming across deep longitudinal scratches and grooves carved into the valley sides. He sensibly concluded that this could mean only one thing – just as the villagers had always believed, glaciers had filled the valley in the past and had carried the boulders along, so it was these that had cut the deep grooves into the valley sides. Whenever an explanation for these curiosities had been sought in the past, philosophers said they were the evidence of the biblical flood, but Perraudin dismissed this as nonsense – he was certain that rising flood water could not move granite boulders. In 1815 he went to present his reasoned conclusions to Jean de Charpentier, born in Saxony and an enthusiast for geology, but Charpentier dismissed the idea as absurd. Undeterred, Perraudin raised the matter with a visiting engineer Ignaz Venetz, who lived in the nearby Rhône Valley, and the evidence he presented was so convincing that Venetz himself approached Charpentier and finally convinced him that the theory was right.37
Venetz worked further on the theory, and became convinced that – just as the hunter Perraudin had concluded – there had been eras in the past where glaciers had existed, and they had left indelible marks on the present-day landscape. He claimed that this proved that much of Europe had previously been covered with vast glaciers. At last it was becoming acceptable to say that the world’s climate truly had changed over time.38
Interest in this subject soon came to the attention of a physician and amateur geologist, Jean Louis Rodolphe Agassiz. He was born in 1807 in Môtier, in the French-speaking part of Switzerland, and qualified in Munich, Germany. He was soon to develop an interest in palæontology and he later studied in Paris under Georges Cuvier, who was greatly impressed by Agassiz’s growing knowledge of fossil fish. When Cuvier died, Agassiz saw himself as his natural successor, and later wrote an extensive work on fossil fish.39
As he developed his spare-time interests in natural history, Agassiz used to discuss his ideas with Karl Friedrich Schimper, a botanist turned poet and four years his senior. Schimper was a firm believer in the idea that prehistoric glaciation had created the landscape they saw around them, and he persuaded Agassiz that the views of Martel and, more recently, Perraudin, provided the evidence. Louis Agassiz devoted much of his free time to tracing changes in the Alps, monitoring snowfall and recording temperatures, and eventually he published an extensive monograph on glaciation. The title page of his book bears a vivid engraving of a glacier towering high above forest trees, and much of the contents comprises a comprehensive collection of detailed climatological tables.40
Agassiz owed his inspiration to Schimper, and to those who preceded him. Scholars have drawn attention to the way in which Agassiz not only failed to give them due credit, but sought actively to conceal it. In 1846, confident that his international reputation was assured, and that his mentors had been eclipsed, Agassiz emigrated to the U.S. and spent the rest of his life as a professor at Harvard.41
Since the revelations in the Alps that Pierre Martel documented more than 270 years ago, we have come to accept the occurrence of ice ages.
We have not always reached the right conclusions. Just 40 years ago, instead of the warmer world we are currently experiencing, people were heralding a new ice age by the end of the last millennium. Global cooling, not warming, was the threat that the public were warned about. Two of my friends wrote books prophesying an era of intense cold. In 1976 John Gribbin published Forecasts, Famines and Freezing and Nigel Calder wrote The Weather Machine and the Threat of Ice. Both confidently assured their readers that we were about to plunge into a new ice age and told how in the temperate latitudes we would need to retreat below the surface to create insulated, habitable cities in order to survive an icy future.42
Calder’s book followed a mammoth BBC television documentary in which he warned us that an ice age was imminent. However, a survey of all the scientific publications on climate in the 1970s shows that only 10 per cent upheld the idea of a new ice age. Even then, most academic opinion was beginning to point to the era we are now experiencing – a time of rising temperatures.43 Most papers were typified by one in Science in 1975, in which Wally Broecker coined the term ‘global warming’.44
This prediction can be traced back to the Swedish scientist Svante Arrhenius, who discovered the relationship between carbon dioxide in the air and the temperature of the atmosphere as long ago as 1896.45 Arrhenius followed this in 1908 with a book in which he suggested that we should expect a gradual warming of our world. He calculated that a doubling of the CO2 in the atmosphere would raise Earth’s average temperature by about 10°F (5–6°C) – an estimate still used by many researchers today.46
Between 1938 and 1957 a British engineer named Guy Callendar published a series of 26 papers that set out to relate the atmospheric increase in CO2 to rising temperatures. Then in 1953 Canadian physicist Gilbert Plass reviewed Callendar’s results and calculated that, if the concentration of atmospheric CO2 were to double, the global temperature would rise by about 7°F (3–4°C). This was a meticulous and important paper, but it was ignored by scientists. Plass was a professor at Texas A&M University when writing his paper and, because his university was regarded as undistinguished, his crucial conclusions were ignored. Academic snobbery drowned his prescient proposal.47
For those who want to see more of the way in which those pioneering investigations of climate change have matured into today’s concerns, the most authoritative book on the subject is the splendid volume Experimenting on a Small Planet by William Hay, Professor Emeritus at the University of Colorado in Boulder.48 The first edition appeared in 2013 and runs to some 1,000 pages. It tells a curious story and is excellent bedtime reading, although, as we know, no book on the future of our climate is destined to have a happy ending.
2
Emerging from the Shadows
Philosophers took a long time to accept that the world had once been a different place. The next step up our ladder of understanding was the dawning realization that huge monsters had once lived on our Earth – creatures whose remains we could find, yet whose nature we could not yet discern. It was the insight of a young French naturalist that introduced the revolutionary idea that there had once been gigantic life forms that had long since ceased to exist. This great step was the brainchild of Jean Léopold Nicolas Frédéric Cuvier. Cuvier – known ever since as Georges – became the greatest naturalist of his age in France, and arguably in Europe. He was born in 1769 in the ancient town of Montbéliard, nestling close to the border with Switzerland, which at the time was ruled by Germany. His father, Jean Georges Cuvier, served in the Swiss Guards, and his mother, Anne Clémence Chatel, was devoted to him and spent much time teaching him. By the time he went to school he showed a fearsome eidetic memory and could recite in detail the chronology of kings and queens, princes and emperors. An enduring fascination for unravelling the past drove his lifetime of study. As a boy, working with his mother, the young Cuvier pored over the antiquated works on natural history by the great French naturalist Georges-Louis Leclerc, Comte de Buffon, and also those by Conrad von Geßner, the influential Swiss zoologist. As a result, by the age of 10 Cuvier was fully conversant with zoology and the classification of all the main animal types.1
Throughout his twenties, Cuvier became increasingly interested in fossils. In 1796 – aged just 27 – he was elected a member of the Academy of Sciences in Paris and presented his first paper on the comparisons between Asiatic and African elephants, and the fossilized remains of mammoths. He listed the differences between African and Asiatic elephants and clearly showed that they were distinct species. Cuvier carefully concluded that the fossils must represent creatures that were extinct. Some of the fossils he studied were of the animal still known as the ‘Ohio Animal’ – the monstrous bones were first excavated in the U.S. in 1739 and were always thought to be the remains of elephants. Cuvier demonstrated that they were anatomically distinct, and he subsequently proposed the name ‘mastodon’. Later that year he spoke of a huge skeleton that had been excavated in Paraguay. He compared its skull with the appearance of present-day sloths, and concluded that this was another kind of gigantic ground-dwelling sloth. He decided to name it Megatherium. These were two crucial papers – first, they demonstrated the value of comparative anatomy, and they also established the view that there were huge forms of life which no longer existed. The young Cuvier ensured that the idea of extinct giants was formally established, and his two lectures set the science of palæontology onto a firm footing.
In 1784 an Italian philosopher, Cosimo Alessandro Collini, reported on a curious fossil that had been dug out of the smooth, creamy Solnhofen limestone in Bavaria. The fossil was part of the cabinet of curiosities in the palace of Charles Theodore, Elector of Bavaria at Mannheim, and it had perfectly preserved wings. Collini concluded that these were the remains of a sea creature with huge fins, though a French/German naturalist named Johann Herman insisted that the fossil represented some kind of bat. Collini heard of Cuvier’s growing interest in fossils, and wrote to him about it, and by 1801 Cuvier had concluded that the fossil represented a flying reptile. He gave it a name we recognize today: ptero-dactyle. Other investigators continued to debate its true nature; it was sometimes claimed to be a bird, a catfish, or a lizard. Not until the 1860s was the nature of a pterodactyl – as a winged reptile – generally agreed.2
It was also Cuvier who recognized the true nature of Johann Scheuchzer’s fossilized skeleton; in 1812 he correctly identified it as a fossil salamander. Until that time the petrified remains had been accepted by every scholar as evidence of a drowned man from the biblical flood, and it fell to the French philosopher’s genius to reveal the truth. The specimen had been purchased by the Teylers Museum in Haarlem, the Netherlands, in 1802 and it remains there on display to this day. It was formally named Salamandra scheuchzeri by a German botanist, Friedrich Holl, in 1831.
Cuvier’s work was widely disseminated and in 1799 it came to the attention of a physics professor in the Netherlands, Dutch scientist Adriaan Gilles Camper. He had been contacted by both Hoffmann and Drouin about the ‘monster of Maastricht’ to resolve whether it truly was a fish, a crocodile or a sperm whale. The fossil had remained a mystery and in England it had become a topic of fascination for James Parkinson, a young and enthusiastic physician with a passion for geology. Parkinson didn’t enjoy trudging over rocks and was no great enthusiast for fieldwork. He obtained most of his specimens from the London dealers and eventually amassed a collection of over 3,000. Parkinson became Britain’s leading palæontologist.
Meanwhile, an enthusiastic student of rocky strata was a young resident of southern England who spent much of his time collecting in the field. This bright young man was Gideon Algernon Mantell, born in Lewes, Sussex, on February 3, 1790, an enthusiastic youngster destined to study medicine and eventually to become a leading obstetrician. Although medicine was to be his profession, his enduring passion was the study of fossils. During Mantell’s childhood, words like geology, scientist and palæontology were largely unknown. There was, however, nothing new about the term fossil. It derives from the Latin fossilis, the past participle of the verb fodere, ‘to dig’, and once meant anything excavated from the ground. It acquired its modern-day meaning in the 1730s, some 70 years after Robert Hooke was writing about fossils in his book Micrographia.
The young Mantell was keen to meet the great James Parkinson, but the enthusiasm was not reciprocated for several years. This was frustrating for a budding enthusiast, for there were few scientific publications that one could study. Parkinson was persuaded that it was time to publish a formal account, and he compiled three majestic folio volumes entitled Organic Remains of a Former World, each extensively illustrated. They were published in London in 1804, 1808 and 1811 – the last being the same year in which Gideon Mantell graduated from St Bart’s Hospital in London. In later life, the elderly Parkinson was more inclined to meet Mantell, and eventually they became firm friends. Parkinson wrote:
I am totally ignorant of the science [of fossils] which teaches us their natural history … I find myself so totally ignorant of their origin, as not even to know in what class of nature’s works to place them.3
This was an honest reflection of the degree of understanding at the time, and his three volumes represent an impressive collation of what was then known. There are separate sections dealing with fossilized shells and familiar marine creatures, of course; and he went on to describe fossils of what he concluded were whales, crocodiles, elephants, mastodons, and even several rhinoceroses. Petrus Camper, the Dutch physicist, had by this time speculated that perhaps a fossil he had found was the skull of a giant monitor lizard, and in 1808 Cuvier agreed. Cuvier published an engraving of what he called ‘the large fossil animal of the quarries of Maastricht’ and he decided to name it Mosasaurus, after the River Meuse, near where it was found.4
Parkinson later reproduced the illustration as Plate XIX Fig. 1 in his own book. The original specimen taken back to Paris by Napoleon’s troops is still on display at the Muséum National d’Histoire Naturelle in the Jardin des Plantes, though the Netherlands authorities have recently been demanding its return.
Nobody dwelled on the significance of these early finds; the fossilized remains of seashells continued to be taken by everybody as proof of the biblical story of the flood. Similarly, when three-toed dinosaur footprints were found preserved in rocky strata, they were conventionally regarded as the marks left by the raven that Noah had sent out looking for land. The significance of these fossil remains lay in verifying the Bible. Without an understanding of prehistory, those biblical interpretations were the obvious first point of reference. Quarrymen and miners used to keep fossils, knowing that they might be sold to collectors. In 1676 a curious stone relic was discovered in the Stonesfield quarry in Oxfordshire, a place that was eventually to become a leading source of fossils for the Victorian palæontologists. It was a strange bilobed object and was purchased by Sir Thomas Pennyston, who later agreed to present it to Robert Plot at Oxford. At that time, Plot was still busily setting up the Ashmolean Museum and he published a report on the find in his Natural History of Oxfordshire in 1677.
I have one dug out of a quarry in the Parish of Cornwell, and given me by the ingenious Sir Thomas Pennyston, that has exactly the Figure of the lowermost part of the Thigh-Bone of a Man or at least of some other Animal, with capita femoris inferiora, between which are the anterior … and the large posterior Sinus: and a little above the Sinus, where it seems to have been broken off, shewing the marrow within of a shining Spar-like Substance of its true Colour and Figure, in the hollow of the Bone. In Compass near the capita femoris, just two foot, and at the top above the sinus measures about 15 inches: in weight, though representing so short a part of the Thigh-Bone, almost 20 pounds.5
His suggestion that this came from an animal proved to be prescient, and for a time he interpreted the bone as coming from a Roman war elephant, though his later interpretation was that it came from a gigantic human.6 Philosophers at the time accepted that 10-foot (3-metre) giants had lived in the past, for they were mentioned in the Bible.7
What Plot was describing was actually the end of a fossilized long-bone. His published engraving is the first we have of a dinosaur bone, even though nobody at the time realized its significance. Plot himself was an enthusiastic naturalist and collector who met many of the luminaries of his day and carefully cultivated their acquaintance. Plot saw himself as Britain’s answer to Pliny the Elder; just as Pliny had written his Natural History, so Plot resolved to publish a Natural History of his own that would commemorate his lifetime’s work.8
Plot’s description of the fossil was meticulous, though he did not assign a scientific name to the specimen. His illustration was re-published by Richard Brookes in 1772. Brookes was a physician and naturalist who wrote a great many books on British wildlife, and his desire to categorize species correctly obliged him to find a suitable designation. Considering its appearance, and disregarding Plot’s attempt at a detailed description, it seemed to Brookes that he knew what it was. There was only one name that unambiguously summed up its appearance: in the fourth volume of his New and Accurate System of Natural History he boldly named it ‘Scrotum humanum’. It certainly looked like one.9
This fossil was found in the Stonesfield quarry near Oxford in 1676 and given to Robert Plot. He identified it as ‘Scrotum humanum’ but is it actually part of a Megalosaurus. His published engraving was the first illustration of a dinosaur bone.
Observation and the art of seeing were becoming a philosophical preoccupation of the learned classes at this time; it was even the subject of literature for children. A six-volume book entitled Eyes or no Eyes; or, the Art of Seeing, written by John Aiken and his married sister Anna Barbauld, was published in 1780. It told the tale of two brothers who walked together in the countryside; one finding it a tedious trip, with nothing of interest, while the other was endlessly engaged in the plant species that they encountered, the myriad insects and meadow creatures he could see, and the geology of the landscape – even finding traces of a prehistoric encampment. It was not what you could see that mattered, but what you perceived. The book was so popular it was frequently republished and remained constantly in print for well over a century.10 So successful was the book that the celebrated W. S. Gilbert and Arthur Sullivan later wrote an opera with the same title.
When Gideon Mantell was growing up in Sussex, the rocky strata around his home were rich in fossils of oyster-like shellfish along with ammonites and belemnites, both of which we now know had swum by jet propulsion like cuttlefish. There was little surprise at the sight of those fossils among the village folk who discovered them. Clearly, they were further evidence substantiating the biblical descriptions of the flood. The shellfish were believed to have been deposited during that inundation, while the coiled shells of ammonites were regarded as serpents that had been turned to stone and the pointed belemnite fossils were taken to be thunderbolts. Collecting these fossilized remains was a popular hobby among youngsters, and young Gideon’s enthusiasms were triggered by the discovery of an exquisite ammonite fossil when he was about 12 years old. Even though palæontology was a word yet to be coined, the collecting of fossils now had a term: oryctology. It is now forgotten and absent from most dictionaries (it has no page in Wikipedia), having originated from the Greek oryktos meaning ‘formed’. And so, by the time Gideon was grown, he was already a seasoned oryctologist.11
It was Mantell’s desire to become a physician that took him to St Bart’s Hospital, where his collecting in the field was replaced with the purchasing of fossils from London dealers including Joseph Stutchbury. Many of the doctors at Bart’s were fascinated by fossils, including the celebrated anatomist John Hunter, and many of those doctors simply purchased curiosities from dealers. In 1790 Hunter wrote a revolutionary account of fossils. Wisely, he proposed that the layers of marine fossils he observed had not resulted from the biblical accounts of a flood, and he concluded: ‘Many retain some of their form for many thousand years …’12
By this time, the way in which layers of rock were laid down in succession had become a fashionable subject for study in Germany. First to write authoritatively on the subject was a mineralogist born in 1714, Johann Gottlob Lehmann. He studied at Wittenberg and was subsequently invited by the Russian Academy of Sciences to move to St. Petersburg and expand his work. Rocky strata seemed to him amenable to serious scientific study, and he realized that they must have been laid down in strict order. In one mining area he identified more than 20 strata, which he called Flötzgebirge, and he soon realized that studying the sequence could perhaps allow prospectors to locate mineral-bearing strata. He concluded that this could be a key to the discovery of vast mineral riches.13
The idea was taken up by Abraham Werner, a young mineralogist who had studied at Freiburg, Saxony, and Leipzig. What a curious man was this – sensibly enough, he taught students that rocks were laid down in an orderly fashion, the study of which could help to ascertain where minerals would lie; but, although he never travelled, he confidently concluded that the sequences he observed in Saxony were representative of those everywhere else on Earth, and he decided that volcanoes resulted from the combustion of coal measures deep below the ground. He had a captivating and charming manner. His students hung on every word. He was only 36 when he published a definitive analysis on a classification of mountain ranges that quickly became essential reading for all budding geologists.14
Ücretsiz ön izlemeyi tamamladınız.
