In March 1835 the naturalist Charles Darwin's was on his first expedition over the Peruvian Andes when, as he surveyed the mountain peaks and deep valleys, his at­tention was suddenly drawn to a small, shiny object in a nearby rock wall. Up close, it proved to be a seashell. Then he saw numberless shells protruding from the same pale band of limestone.

He knew that the elevation was around 13,000 feet. His mule-drivers had been complaining about the cold, and in that rarefied air Darwin was suf­fering shortness of breath. The naturalist could have reaped a large harvest had he remained for several days. But the discovery had come late in the southern sum­mer; if snow began falling, the expedition, already suf­fering under the severe conditions in the high Andes, might find itself trapped.

As Darwin gathered his fossil shells, he saw that some were similar to ones he had previously collected on the beaches of the Pacific Ocean far below. Presumably they had at some time in the past rested on the ocean bottom. Through some unknown process of upheaval, the once low-lying beds had been elevated to a height of 13,000 feet.

Darwin concluded that the Andes had not been wholly created by the molten outpourings of volcanoes, as geologists had hitherto believed. Today, we know that Darwin was right. The friction of the Earth's slowly drifting crustal plates has in many re­gions wrinkled the ocean floors and pushed up great mountain ranges along the edges of several continents.

The fossils Darwin collected on this high mountain helped to change his ideas and ultimately those of the world about the age of the Earth. For such shell-bear­ing sediment to have been uplifted from sea floor to mountain crest would have taken millions and millions of years, Darwin recognized. And Darwin knew that the Andes shells were not an isolated case. Similar fos­sils had been discovered previously in the Alps and other mountain ranges.

The fossils buried in the rocks could be read, in a sense, like a geological calendar of the past, recording the succession of eras in the Earth's history, each with its characteristic forms of life. As long as there were no violent disturbances, the oldest stratum of sedimentary rock, containing the oldest shells, would lie at the bot­tom of any series of sediment layers. The younger ocean sediments, with younger fossils, would necessar­ily be deposited on top of the older layers on the ocean bottoms. If the strata were undisturbed, the order of the ages would be as clear as numbered pages in a book.

In addition to the evidence fossils give of past geo­logic processes, they offer concrete records of organ­isms that no longer exist on the Earth. Down through the ages, the remains of countless creatures have drifted to the ocean bottoms. Although most were perishable, many possessed hard parts; their impressions were cast and preserved in the sands, sediments and silts of the ocean floors-and were buried under the continuous rain of other organic debris settling to the sea floors. On land, fossil creatures have been preserved in tar pits, bogs, swamps, caves, stream beds, ice sheets and other sites.

For centuries before Darwin's Andean discovery, of course, many other people had found shells and bones at various places on the Earth. The ancient Greeks had picked up seashells far inland from beaches, reasoning that the sea must once have rolled in over the land where they lay. Occasionally a huge fragment resembling the bone of a giant animal might be discovered -only to be attributed by the Greeks to a mythical monster.

In following centuries people continued to find the fos­sil remains of sea creatures on dry land. Few, though, knew of the Greek explanation of changing sea levels in the past, and even fewer accepted the Greek theory. Some learned men believed the fossils to be foreign bodies grown on the Earth from seeds that had fallen from the stars; other scholars argued they must have formed in the ground in chance imitation of life. Still other thinkers deduced that they were the works of Satan-buried in the ground to deceive curious men.

In 17th-century Europe the puzzle posed by fossil remains took on a new significance. Church scholars were shocked as they saw the Bible being subjected to various readings and translations. To uphold the long-accepted Biblical authority upon which society and re­ligion rested, religious leaders undertook to prove by contemporary scientific methods that the miracles-and particularly the account of creation-were true. Scien­tific certainty was to support scriptural revelation.

Fossilized Micro-organismsCertainly the disconcerting evidence of strange fossil creatures on the Earth had to be accounted for. John Ray (1627-1705), a Cambridge University scholar, was too good a naturalist to attribute fossils to seeds from remote stars or the work of the devil. He saw that the fossil shells he collected inland were, in fact, not at all unnatural; they were exactly like those- washing up on the beaches even then. Other inland finds were the skeletons of fish that he knew inhabited the ocean depths.

Ray accepted church doctrine that the marine fossils found on land were evidence of the Biblical Flood. But why were they not spread more evenly across the Earth, he wondered, instead of being amassed or lumped within layers of rock? And why did the fossil troves sometimes contain the remains of species that were not known to exist on the Earth? Hadn't all present-day terrestrial animals descended from those Noah rescued in the ark?

During the 40 days and nights of the scriptural deluge, Ray concluded, the so-called waters of the abyss - reservoirs thought to exist in the bowels of the Earth and to connect with the waters of the oceans - must have filled to overflowing. Under these tremen­dous pressures, the floodwaters burst forth, he wrote, "at those wide Mouths and Apertures made by the Di­vine Power breaking up the Fountains of the Deep." The concentrations of fossils at certain sites on land were thus satisfactorily explained. All appeared to be once more in order, even though Ray did not explain the remains of creatures nonexistent on the Earth.

Less than a century later, new fossil finds made it impossible to ignore these strange anomalies any longer. The French naturalist Baron Georges Leopold Cuvier (1769-1832) began to find the fossilized bones of ele­phants, flying lizards and other fantastic animals in the soil around Paris. People in Paris rushed out to the gyp­sum quarries where he was unearthing the bones to witness the spectacle. Cuvier caused an even greater sensation when he reconstructed many of the skeletons to suggest the appearance the animals had in life.

"Is Cuvier not the greatest poet of our century?" ex­claimed the popular French novelist Honoré de Balzac. "Our immortal naturalist has reconstructed worlds from blanched bones. He picks up a piece of gypsum and says to us, 'See!' Suddenly stone turns into animals, the dead come to life and another world unrolls before our eyes."

The lost menageries that Cuvier was suddenly pro­ducing, as though possessing powers of a sorcerer, were not a random assortment, by any means. The animals of the past - like those of the present - can be classified as birds, mammals, reptiles and so forth.

As he unearthed these ancient remains from their beds of rock, Cuvier saw that the sea fossils always lay within their own stratum, while the fossils of land crea­tures occupied a separate layer. Between the marine and terrestrial groupings might fall a stratum that held no fossils whatsoever. Cuvier theorized that this part of France must have lain under the sea; during this time the stratum containing marine fossils was deposited as sediment. Afterwards, the waters had receded; hence, the fossils of land animals appeared in a separate sedi­ment layer laid down by lakes and rivers. Many such successions had occurred in the region.

At almost the same time as Cuvier was causing a stir in France, similar discoveries were being made in England. In 1811 Mary Anning, a carpenter's daughter, found the skeleton of a 21-foot marine reptile in a crumbling cliff on the south coast. William Smith, an astute geological observer then employed as a surveyor and an engineer in digging Britain's new canals, saw that in the newly excavated banks of canals lay strata of rock, each characterized by a certain type of fossil remains. He realized that rock strata, judging by their fossil content, seemed to be laid down everywhere on the Earth in an orderly sequence. Smith prepared a map of Britain, showing, in his words, that "the same species of fossils are found in the same strata, even at a wide distance."

Through their observations Cuvier and Smith helped to develop geology as a real science. Although most other scientists of the time were willing by then to grant that fossils were the remains of actual animals, few suspected that those remains and their associated rock layers gave a clear record of the past-or that they could be used to determine the order of events in the Earth's history.

Shortly thereafter, in 1860, while digging in a lime­stone quarry in Bavaria, Germany, workmen came upon a remarkable fossil imprint. Nothing like it had ever been seen before by anyone. It was a cast of a creature the size of a chicken, with sharp teeth, an elongated head, an extended neck and strong hind legs - all reptilian characteristics. But the cast also showed, in exquisite detail, the unmistakable impression of feath­ers on a wing that had claws. If the impression of the feathers had not been preserved, who could have guessed at their presence? Was this toothed animal with claws bird or reptile? Later two more casts of the creature were found.

Presumably these birdlike reptiles had fallen into the waters of the coral lagoon that had covered this region in the remote past and been buried in sediment of tiny marine shells. As the skeletons of the small marine or­ganisms settled over the bodies of the reptile-birds, the latter were preserved with their features cast in sharp de­tail. Later, this soft ooze of bottom sediments hardened into limestone so that the cast had lasted some 135 mil­lion years or more-long after the lagoon had dried up.

This prehistoric creature of the air was named Archaeopteryx (ancient bird), sometimes called Urvogel (original bird in German). It is now known to be one of the earliest and most primitive of a group that evolved into our modern birds.

Archaeopteryx was soon followed by numerous fos­sil discoveries, each enlarging our perspective of the Earth's past. Smooth-grained, limy lagoon floors and the dried-up bottoms of ancient shallows disclosed the crawl-trails - sometimes even footprints - of early crawl­ing and wading forms of life.

In beds of rock now raised high and dry, fossil hunters came unexpectedly upon the meandering, scratchy paths traced by insects millions of years in the past. Here, perhaps, the trail of a tiny crab was afforded a permanence far exceeding the lifetime of humanity; while there, the footprints of extinct birds were found perfectly cast in solid, endur­ing stone. Other rocks held evidence of the tracks of long-departed dinosaurs.

At sites such as the chalk cliffs of Dover and else­where along the English Channel, beds of limestone thousands of feet thick were found actually to be fossil graveyards. Such deposits had formed from the cal­cium-rich skeletons and shells of small marine organ­isms collecting in ocean sediment over tens of millions of years. Some of the shells-like those Darwin had gathered high in the Andes-were discovered intact amid the chalk. In the vast majority, physical change had occurred, transforming them into the chalk itself. Occasionally the original structure of shell, bone or plant tissue had been replaced by minerals precipitating from the waters - forming petrified remains. Thus, the sea floors and the sedimentary rocks of the continents were recognized as vast burial grounds of the past.

Only more recently has the extent of the record on the ocean bottoms been comprehended by scientists. In the past few decades, oceanographers have been drilling from shipboard into ocean sediments and their underly­ing rocks. The drilling rigs of the special explora­tory ship Glomar Challenger for instance, was owned by the University of California and launched in 1968 were lowered through as much as three miles of water to reach the top of sediment deposits. Then, drilling into the sedi­ment, researchers brought back drill cores from almost 4000 feet - four-fifths of a mile farther down. These tubular cores consist of many layers of sedimen­tary material, whose cross sections depict the history of the sea floors in periods of tropical warmth and glacial cold and in their gradual movements outward from the mid-ocean ridges. Furthermore, for rather long periods there is a continuous record on the sea floors of the evolution of life. On land, this is seldom so, because of the disruptive forces of wind and water erosion which strip away accumulating soils and strata. Many thousands of such cores have since been extracted all around the world, including the Poles, since these early days of oceanography.

For many years the records discovered in the rocks had stopped short of disclosing evidence of early man. Cuvier had argued that there would prove to be no such thing as fossil man, and Darwin himself could cite no fossils that seemed to lie in their development be­tween the apes and mankind. But in 1868 a fossil skull of a man with a pronounced low brow, and with other traits seemingly more primitive in development than those of modern man, was found in the Neander Val­ley in Germany.

Some authorities insisted that the Ne­anderthal skull was only that of a deformed individual of the species Homo sapiens. Darwin's friend and sup­porter, the British naturalist Thomas Huxley, stated that Neanderthal man could not be regarded as an in­termediate evolutionary form; rather, Huxley believed, he had been an advanced human being, even though an unusual one. But Huxley did pose the question whether in some older strata some future paleontologist might not find the fossilized bones of a more manlike ape, or a more apelike man, than any remains then known.

In 1887 Eugene Dubois, a young Dutch physician, uncovered on the island of Java in what was then the Dutch East Indies the fossil bones of a specimen he called Pithecanthropus erectus (the upright ape-man). Java man, as he has since become known, possessed a flattish skull somewhat apelike in appearance. The shape of his thigh bone, though, indicated that he had walked upright, like a human.

Peking ManPublic outrage ran high at Dubois' claim to have found an early ancestor of man. Many people could not accept the possibility that modern man had descended from such primitive stock. Shortly after the discovery of Java man, however, a similar fossil skull was found in a cave at Zhoukoudian, near Beijing. It was called the Peking (former name of Beijing) man. The two pieces of evidence at such widely separated points in Asia suggested that a species of man more primitive than Homo sapiens had once ranged over much of the Orient.

In 1924 Dr. Raymond Dart, a professor of anatomy at South Africa's University of Witwatersrand, identi­fied a fossil from a limestone quarry at Taung as the skull of a six-year-old child with a brain case no larger than that of a young ape, but with other clearly human traits. Not until 20 years later were enough adult skulls of this same type recovered by another South African paleontologist, Dr. Robert Broom, to confirm that these early creatures were not slightly unusual chimpanzees but higher forms of primates more closely allied to humans, despite their small brain case and small sta­ture.

These creatures are known as Australopithecines (southern apes). The potassium-argon method of radio­active dating has found some of the Australopithecine remains to be as old as 2.5 million years.

It is in this same region of Africa where the Austra­lopithecines once flourished that more advanced and recognizably manlike beings eventually are believed by anthropologists to have arisen, probably as descendants of the Australopithecines. If the Australopithecines can­not quite qualify as the first men on the Earth, their descendants do and it is widely accepted that all humans originally descended from ancestors in what is now Africa.