From Origin of Life till Appearance of Man
How old is the earth? How long has man lived on it? In the past few years scientists have found much new evidence for answering these two questions.
Geologists, scientists who study the crust of the earth and its strata, or layers—believe that the earth is approximately 4½ to 5 billion years old.
According to scientific theories, the earth began as a flaming mass of gas and vapour that gradually cooled enough to harden. Clouds appeared and for millions of years dropped rain onto the hot surface of the earth. The heat turned the rain to steam, which again became part of the overhanging clouds. As the earth cooled still more, the fallen water collected as deep oceans and shallow seas, which covered most of the earth. It was in these oceans and seas that living things first appeared. And with them begins the story of life on earth. Living things developed from simple to more complex forms. Scientists believe the first living things—which existed at least a billion years ago—were simple one-celled, water-dwelling plants and animals.
These tiny bits of living matter had no bony structure. As advanced life forms developed, they became more complex; that is, they were composed of more than one cell. Jellyfish, worms, snails, crabs, and then fish appeared in the water. The hardened remains of these life forms are called fossils. All the earliest life forms lived in water. From them developed amphibians, which could live on land as well as in the water.
Later, great reptiles such as dinosaurs appeared. And, after a long time, birds and higher animals developed. Each stage of animal development took millions of years. Conditions were not easy for these early life forms. They had to struggle against other living things and against the strong forces of nature. Many plants and animals could not survive. Others did survive and became stronger as new generations changed to meet conditions on the earth. Some animals changed a great deal.
For example, millions of years ago horses were only a foot high, with four-toed front feet and three-toed hind feet. Skeletons gave clues to the appearance of early man. Although many theories about the origin of man exist, scientists believe that man came into being quite late in the long span of the development of life on earth—about 2 million years ago. Scientists have important clues to what the earliest men looked like. These clues are determined from the remains of ancient skeletons. Anthropologists can reconstruct the probable shape of an entire body from the bony parts which have been found. In 1891 and 1892, Eugene Dubois, a Dutch surgeon and anthropologist, found the top of a skull, three teeth, and a left thighbone in a dry river bed on the island of Java.
From these remains, anthropologists have reconstructed a type of early man which was called Java Man. He was shorter than the average man of today. His head hung forward on his chest, and his strong teeth and jaws stuck outward. His skull was small and very thick, and his forehead sloped back. Java Man, who probably lived about 500,000 years ago, was considered the oldest known man until the mid-1900’s.
In 1959, Dr. L. S. B. Leakey, a British anthropologist, made exciting discoveries in Tanganyika (now called Tanzania) in East Africa. Dr. Leakey unearthed the skull of a near-man, estimated to have lived 1% million years ago. This East Africa Man, which he named Zinjanthropus, was lowbrowed and long-faced, with large, deep jaws. In 1964 Leakey announced another discovery, which he called Homo habilis (“man with ability”). Though Homo habilis lived about the same time as Zinjanthropus, he was more advanced. His teeth were not so worn down as earlier types, showing that he did much of the work of grinding and cutting with stone tools. Dr. Leakey claimed that Homo habilis was a direct ancestor of modern man. Before Leakey’s discoveries, parts of the skeletons of other early men had been found in Asia, Africa, and Europe.
Peking Man is considered to have been more advanced than Java Man. Other finds included Heidelberg Man, Neanderthal Man, and Cro-Magnon Man. The study of the skeletons of these finds show the changes that occurred in man over thousands of years. The brain became larger, the teeth became smaller, the legs became longer and straighter, and a more erect posture was developed. The skeleton of the Cro-Magnon Man was much like that of modern man.
