Age Of Mammals
( Originally Published Early 1900's )
A NEW AGE OF LIFE
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 toady 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 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 as 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. We may be moving now towards a warmer phase. Half a million years hence this may be a much sunnier and pleasanter world to live in than it is today.