Prehistoric Times: The World Before Man (1952)

Jimmy wants to be a scientist someday, and he likes to go exploring. Along the shores of the lake where he lives, he collects stones as a hobby. Strangest of all are small stone discs which have a hole through the center. Jimmy has learned that these discs were once the stem-like part of a simple animal that lived in an ancient sea millions of years ago. Resembling a flower, this animal was one of many forms of prehistoric life. Scientists can show us what these forms looked like from evidence they have found. For instance, this prehistoric kind of crustacean is called a trilobite. Geologists have found the remains of this ancient type of animal in the form of stone casts, which are one type of fossil. Fossils are part of the prehistoric evidence that has helped geologists reconstruct prehistoric times. From their studies of other kinds of evidence in the Earth's crust, many scientists estimate that the Earth is two or more billion years old. This time of about two billion years, scientists have divided into five great periods of time called geologic eras. During the first billion years, the Archeozoic era, continents and seas were forming. In the next half billion years, the Proterozoic era, simple forms of plants and animals appeared in the seas. The Paleozoic era of 300 million years was an age of underwater animals including fishes. Then came the Mesozoic Era, 125 million years during which reptiles dominated the Earth. Today we live in the Cenozoic Era, which began 60 million years ago. During this time appeared mammals, including man. Let's begin with the Archeozoic Era, about 2 billion years ago. During the first billion years, continents and seas were forming and since that time the Earth has been continually changing. There were periods when mountains were built up from the seas by volcanic action. Sometimes whole mountain ranges were built by volcanic action and by other slower forces, some of which pushed up rocks into great mountain folds. On the other hand, forces of erosion such as running water, wind, rain, and ice were wearing down the mountains and other high regions. The process of erosion is slow. The land wears away bit by bit. This process of building up and wearing down has been a continuous process. Even the oceans were changed in size and shape. Scientists think that during the latter part of the Archeozoic Era, in the warm seawater that covered much of the land, living matter appeared. Many scientists believe these earliest forms of life were tiny one-celled plants and animals, something like the one-celled amoeba. The long billion-year Archeozoic Era gave way to the Proterozoic Era. During this time, there is evidence that there were more complicated forms of plants and animals, probably similar to the tiny crustaceans and simple green algae we we today. Following the half billion years of the Proterozoic era, came Paleozoic times. At the start of this 300 million year era, there is no evidence of life on the land. But beneath the surface of the warm seas, the waters were teeming with prehistoric plants and animals. Among the early Paleozoic animals were the corals. Like corals of our seas today, they built hard external skeletons. Some of them lived in colonies. Among other forms of life in these ancient coral reefs, were animals called cephalopods. Some of them attained a length of 15 ft and were masters of the seas. The prehistoric cephalopods were related to the octopus of present-day times. The octopus has no backbone and no outside shell. However, during Paleozoic times, many cephalopods lived in elaborate shells. Important animals in the seas of mid-Paleozoic times were the fishes. Fish are vertebrates, animals with backbones. Among the early fishes was the lungfish. This present-day lungfish occasionally comes up to breathe air, just as these prehistoric lungfish did. More suited to life on the land were air-breathing amphibians. Living both in the water and on the land, the amphibians were part of the world of plants and insects of Paleozoic times. Dense forests of ferns and other kinds of plants grew in the warm, moist climate. It is from the trees and other plants of these Paleozoic forests that we get much of the coal we use today. The forests grew in great swampy lowlands, and when the trees died, they fell into the water and were covered with mud. With the passing of millions of years, they were changed into the coal we find today. So, this period of large coal forests is called the coal age. By the end of the coal age, air-breathing lizards had appeared. With the coming of these reptiles, the long Paleozoic era was drawing to a close. The next era, the Mesozoic, is often called the age of reptiles. It was a time of tremendous volcanic eruptions. Of all the life on the land, the lizards were among the animals that survived the violent upheavals. Gradually, gigantic reptiles came to dominate the Earth in the Mesozoic era, the age of reptiles. We call them dinosaurs, the Latin word for terrible lizard. This one had thick, armor-like plates along its back and was about the size of an elephant. Such huge, plant-eating dinosaurs were often attacked by vicious, flesh-eating reptiles. But, the fierce dinosaurs were not the only reptiles on the Earth. Reptiles with great, webbed wings, related to prehistoric birds, were also part of the Mesozoic era. Once again, changes in the Earth's surface brought this period to a close. With the Cenozoic era came the age of mammals. Among the earliest mammals were some simple types, not too different from the hedgehogs of our present day. This sloth was one of the common types of prehistoric mammals. Among the largest mammals of Cenozoic times were the mastodons, whose bones we still find in many parts of the earth. These great elephant-like animals were among those that lived during the severe climatic changes that happened during the ice age, which began about a million years ago. There were times when large portions of the earth were completely covered with glacial ice and snow. Living on the tundra near the edge of the ice fields were the woolly rhinoceros and the huge mammoths. The great shaggy mammoths belonged to the elephant family. They were related to the elephants on the earth today. In the same way, the horses that we know today can be traced to their prehistoric ancestors, small horses that roam the earth millions of years ago. The story of the horse and other mammals is only part of the evidence of prehistoric life that scientists are continually finding. Scientists estimate the age of the earth at some 2 billion years or more. The first great era is called Archaeozoic, the time of the formation of the earth's crust. In the next era, the Proterozoic, the waters of the earth contained simple forms of plants and animals. During the Paleozoic era, animals without backbones were most important. About the middle of this time, fish with backbones became abundant. And near the end of the era, air-breathing amphibians and lizards appeared. Giant reptiles called dinosaurs came to dominate the earth during the Mesozoic era, sometimes called the age of reptiles. And in the most recent era, the Cenozoic, mammals appeared on the earth. It was toward the end of this era, during one of the warmer stages of the ice age, that man, the most highly developed mammal, appeared. The story of prehistoric man is the last chapter in the long record of prehistoric times.