The Outline of History: Being a Plain History of Life and Mankind

by H. G. Wells

The range of life of the Mesozoic Period as we know it was confined to water and fairly low-lying valley regions under equable conditions.

Meanwhile in each of these periods there were types involuntarily extending the range of life beyond the limits prevailing in that period; and when ages of extreme conditions prevailed, it was these marginal types which survived to inherit the depopulated world.

That perhaps is the most general statement we can make about the story of the geological record; it is a story of widening range. Classes, genera, and species of animals appear and disappear, but the range widens. It widens always. Life has never had so great a range as it has to-day. Life to-day, in the form of man, goes higher in the air than it has ever done before; man’s geographical range is from pole to pole, he goes under the water in submarines, he sounds the cold, lifeless darkness of the deepest seas, he burrows into virgin levels of the rocks, and in thought and knowledge he pierces to the centre of the earth and reaches out to the uttermost star. Yet in all the relics of the Mesozoic time we find no certain memorials of his ancestry. His ancestors, like the ancestors of all the kindred mammals, must have been creatures so rare, so obscure, and so remote that they have left scarcely a trace amidst the abundant vestiges of the monsters that wallowed rejoicing in the steamy air and lush vegetation of the Mesozoic lagoons, or crawled or hopped or fluttered over the great river plains of that time.[16]

VII
THE AGE OF MAMMALS

§ 1. A New Age of Light. § 2. Tradition Comes into the World. § 3. An Age of Brain Growth. § 4. The World Grows Hard Again. § 5. Chronology of the Ice Age.

§ 1

THE third great division of the geological record, the Cainozoic, opens with a world already physically very like the world we live in to-day. Probably the day was at first still perceptibly shorter, but the scenery had become very modern in its character. Climate was, of course, undergoing, age by age, its incessant and irregular variations; lands that are temperate to-day have passed, since the Cainozoic age began, through phases of great warmth, intense cold, and extreme dryness; but the landscape, if it altered, altered to nothing that cannot still be paralleled to-day in some part of the world or other. In the place of the cycads, sequoias, and strange conifers of the Mesozoic, the plant names that now appear in the lists of fossils include birch, beech, holly, tulip trees, ivy, sweet gum, bread-fruit trees. Flowers had developed concurrently with bees and butterflies. Palms were now very important. Such plants had already been in evidence in the later levels of the (American Cretaceous) Mesozoic, but now they dominated the scene altogether. Grass was becoming a great fact in the world. Certain grasses, too, had appeared in the later Mesozoic, but only with the Cainozoic period came grass plains and turf spreading wide over a world that was once barren stone.

The period opened with a long phase of considerable warmth; then the world cooled. And in the opening of this third part of the record, this Cainozoic period, a gigantic crumpling of the earth’s crust and an upheaval of mountain ranges was in progress. The Alps, the Andes, the Himalayas, are all Cainozoic mountain ranges; the background of an early Cainozoic scene, to be typical, should display an active volcano or so. It must have been an age of great earthquakes.

Geologists make certain main divisions of the Cainozoic period, and it will be convenient to name them here and to indicate their climate. First comes the Eocene (dawn of recent life), an age of exceptional warmth in the world’s history, subdivided into an older and newer Eocene; then the Oligocene (but little of recent life), in which the climate was still equable. The Miocene (with living species still in a minority) was the great age of mountain building, and the general temperature was falling. In the Pliocene (more living than extinct species), climate was very much at its present phase; but with the Pleistocene (a great majority of living species) there set in a long period of extreme conditions—it was the Great Ice Age. Glaciers spread from the poles towards the equator, until England to the Thames was covered in ice. Thereafter to our own time came a period of partial recovery.