5. Mineral, Plant And Animal Creation

We are accustomed today to regard the Earth as having always existed in the form in which it appears to us today. We inhabit a continent, we are surrounded by plants, by animals, by birds of the air. We are aware that we ourselves are living in a kind of atmospheric ocean surrounding the Earth, that we take oxygen out of this atmosphere into ourselves but that our relation to nitrogen has also a certain part to play. In general we simply think of the air around us as consisting of oxygen and nitrogen. Then we turn to look at the seas and oceans—further details need not be mentioned—and finally we have a picture of the planet we inhabit in the Universe. But the Earth has not always been as it is today; it has undergone tremendous changes, and if we go back to the epochs I have just mentioned—perhaps only to the Lemurian epoch or a little earlier—we shall find an Earth very different from that of today.