The term “fossil” dates back to ancient times and comes from the Latin fossilis, meaning “that which is obtained by digging”; it originally was used to indicate rocks, minerals and gems as well as all those forms resembling living organisms frequently present in rocks and which for a considerable time remained shrouded in mystery. As everybody knows, fossil in the modern sense of the word indicates the remnants of living organisms both animal and vegetable which over the course of time populated the seas and the lands and which were incorporated and conserved in sedimentary rocks. But this was not always so clear: for more than two thousand years two contrasting theories were advanced concerning the origin of fossils, one inorganic the other organic.
As for the western world, the inorganic theory originates with the Greek philosopher Aristotel (383–322 B.C.), according to whom the shapes resembling living organisms found in rocks were produced by a “formative force” (vis formativa) in some way connected to the heavenly bodies. The Aristotelian School, through a Moslem , the Persian philosopher Avicenna (980- 1037), was a source of inspiration for many European scholars in the Middle Ages and Renaissance, who attributed to a “plastic force” (vis plastica) the power to shape living beings: those objects found in rocks in the shape of animals or plants were considered to be abortive attempts by such force. This road led to the most fanciful speculation, such as the idea that fossils were “freaks of nature” (lusus naturae) produced by natural causes imitating living shapes. All such interpretations, basically subscribing to the notion of the spontaneous generation of life, were discarded around the beginning of the XVIII Century when the nature of fossils was definitively recognized as being the remnants of living beings from former times.
In reality, the idea that objects found in rocks. such as seashells from molluscs or fish vertebrae, were really what they seemed to be, which is to say the remnants of formerly living organisms, appeared even before Aristotel: already in the VI Century B.C. the Greek Xenophon of Colofone reported that “…in the mountains are found shells and in Syracuse in stone quarries are found the imprints of fish and seals (…) and on Malta impressions of fish of every sort”.
For Xenophon this was proof that in ancient times everything had been reduced to mud due to the mixing of the land and sea, and that the remnants of living shapes had remained imprisoned in the dried mud.
In the VI Century B.C. both Pythagoras and Herodotus spoke of seashells found in the mountains or far distant from the seacoast, interpreting them as remnants of organisms living at a time when the sea occupied lands later emerged. But it was in the early centuries after Christ that the idea of the organic origin of fossils took root and spread, although in different form with respect to the Greeks: shells and other remnants of marine organisms found in the mountains were indicated by Church Fathers such as Tertullian (155-222 B.C.) as proof of the Universal Flood described in the Old Testament. The Universal Flood Theory survived along with the astral influence theory all through the Middle Ages and Renaissance and up to the threshold of the XVIII Century.
It is in this early scenario rich in fanciful speculation far from the direct observation of nature that Leonardo da Vinci (1452-1519) appeared in splendid isolation. It was he who first correctly interpreted the nature of fossils and the information that can be gleaned therefrom.
Leonardo ’s ideas emerge vividly from notes, annotations and drawings distributed throughout numerous manuscripts in his hand, particularly in the collection known as the “Leicester Code” wherein often appear memories of experiences and observations in the hills and dales of Tuscany, Romagna or the Po River plain (where he supervised the digging of large canals for hydraulic engineering works).
The problem of the origin of fossils was often in the forefront. Leonardo rejected the ideas of those who held that bivalve shells known as nicchi were formed due to a particular shaping quality found in the ground below or the stars above, because in that case it would prove impossible to find together in the same place – as frequently happens – both young and old specimens (which can be distinguished on the basis of the number of growth marks on the shell surface, another of Leonardo’s discoveries), nor some such intact and others smashed.
Moreover, they would not be mixed with fish-bones and teeth “had they not been accumulated along an ancient beach by the action of sea waves”.
He decidedly rejected the flood theory with the use of supporting arguments: “ … whether the flood was caused by rain swelling the rivers or for a rise in the level of the sea, (…) the nicchi, being heavy, could not have been tossed by the sea to the mountains, nor dragged together by the rivers against the current”. Furthermore, such bivalves are frequently found whole with the two halves still joined just as when they are alive, as can be observed along any beach, while violent flood waters would have broken them up and scattered the pieces, as can be seen wherever the waves accumulate shells along the shore. If does not suffice, we can pose a question: How did the bivalves manage to get to Lombardy under their own power in just 40 days and 40 nights (as he who kept track of the time said”, Leonardo adds ironically) following the advancing floodwaters since they move at a snail’s pace and the nearest sea is 400 kilometres away?
Leonardo’s modernity lies not so much in his conclusions as in his way of reaching them, which method takes as its starting point the careful observation of the past phenomenon under investigation, then confronts the results with the analogous present day situation (observing the life of living molluscs, their natural habitat and the like). His mind, free of prejudice, was then ready to take a giant step toward a better understanding of the Earth: fossils and rocks indicate that at one time the sea covered what was now land – and this discovery led him to the intuition that the Earth’s surface u n d e rgoes constant transformation. Centuries before, the School of Pythagoras had already clearly expressed the same concepts in proclaiming the eternal flux and change of all the world’s forms. As later on Ovid put it in his Metamorphoses: “And I saw what at one time was solid earth transformed into sea; I saw emerge from the waters new lands and far from the shores, abandoned, seashells…” (Ode XV, beginning line 262).
But Leonardo went ever further. Direct experience, intuition and the artistic imagination led him to a much clearer vision of the past which disconcerts the modern reader for its boldness of innovation and power of synthesis. An example is found in his description of the Mediterranean of old which “…received the waters of Africa, Asia and Europe (…); and the Apennine peaks stood in this sea in the form of an island, surrounded by the seawaters (…); and above the plains of Italy, where now fly birds in flocks, great schools of fish used to dart about”. He “sees” what he describes because he has seen the proof on land. A recently discovered example of this ability to observe as well as an anticipation of future scientific discoveries is found in the first conscious depiction of turbiditic strata with laminae clearly visible in the rock where the group of people stands in the painting “Sant’Anna, la Madonna e il bambino con l’agnello”. In the history of geology Leonardo’s ideas unfortunately did not prove to be as fertile as they deserved; locked up in his manuscripts, they were to be rediscovered only more than three centuries later, by which time geology had become a science whose practitioners had reached the same conclusions on their own.
But Leonardo remains if not the founder, the precursor of modern geology. His teachings on how the study of our planet ought to be approached still are as modern today as they were nearly five hundred years ago.