Mars and Its Canals

by Percival Lowell

Following upon the Old Red Sandstone were laid down the Carbonic strata, and with the Carbonic entered upon the scene the advance scouts of an army of progress evolutionarily impelled to spy out the land—the first amphibians. They made their début in the Subcarboniferous section of the era, the oldest of the three periods into which the Carbonic is divided, crawling out of the sea to return again and leaving but footprints at first on the sands of time. In the second period, the Coal-measures proper, they ventured so far as to leave their skeletons on terra firma, or rather infirma, while their tracks there show them to have been now in great numbers. In this manner the ancestors of the oldest land inhabitants began to struggle out of the sea. In the Permian, the third and latest period of paleozoic times, we find their descendants established in their new habitat, for in it we come upon the first reptiles. Such possession marks a distinct step up in function as in fact, for while amphibians visited dry land, reptiles made it their home. The getting out of the water had now, in the case of the more evolved forms, become an accomplished fact. The reptiles were, indeed, the lowest and most generalized of their class, Rhynchocephalians, “beak-headed” species that by their teeth proclaim their marine origin and their relationship to the great amphibians that still felt undecided where to stay. Meanwhile, in Europe dragon-flies, two feet across, possessed the air; while amphibians there, as here, ancestrally preceded reptiles in occupying the land.

Mesozoic times were, par excellence, the age of monsters; for the Triassic (the New Red Sandstone), Jurassic and Cretaceous eras marked the reign of the reptiles. Great dinosaurs sleep still in the Triassic strata of the Atlantic border and in the Jurassic of the Western states, to be unearthed from time to time and be given mausolea in our museums. Gigantic they were and very literally possessed the earth. In Europe they were substantially as in America during these mesozoic eras, and showed their dominance by long survival in time as well as world-wide distribution in space; for they lived all the way from Kansas to New Zealand and from the Trias to the Upper Cretaceous. It is supposed by Professor Osborn that many of them, like the herbivorous brontosaurus, waded in marshes, not wholly unlike in habit to the modern hippopotamus. Others were land-stalking carnivores, like the megalosaurs of a little later date. Of enormous size, the largest exceeded any animal which has ever lived, the whales alone excepted; the biggest, the atlantosaurus and the brontosaurus, reaching a length of sixty feet. For all their bulk they had scant brains, just enough to enable them to feed and wallow, probably. It is interesting to note that many of the reptiles, the less adventurous, apparently reverted to the sea. For though the crocodilians existed already in the Trias, the plesiosaurians did not come in till the Middle Trias in Europe, and the sea-serpents (mosasaurus) till the Upper Cretaceous.

Though the dinosaurs dominated life in those days, higher forms, their descendants, unnoticed were gradually creeping in, eventually to supplant them. For brain was making its way unobtrusively in the earliest of the mammals, diminutive creatures at first and of the lowest type. First appearing in the Trias as something approaching the missing link between reptiles and mammals, they later developed into monotremes and marsupials, not rising in differentiation above the latter order to the end of Mesozoic times. And this both in the old world and the new. In the Jurassic, too, flying lizards and the first birds appeared, showing their pedigree in their teeth.

With Cenozoic times we come upon the first true or placental mammals with their culmination up to date in man. In the Eocene they were of a primitive type; they were also of a comprehensive one, fitted to eat anything. From this they specialized, some evolving and some on the whole devolving; the whale, for instance, taking to the water in the Eocene through the same degenerate proclivity that had characterized the sea-saurians ages before. The earth was growing colder, though still fairly warm, and with the fall in temperature the higher types of life antithetically rose, evolution gradually fitting them to cope with more advanced conditions. In this manner did the land supplant the sea as the essential feature of the earth’s surface, first, in coming into being, and then, by offering conditions fraught with greater possibilities, as the habitat of the most advanced forms of life, both plants and animals.

The possibility of advance in evolution was largely due to the fact that the land did thus supplant the sea. Spontaneous variation, the as yet unexplained primum mobile in the genesis of species, is probably to be referred to chemism and is likely later to receive its solution at the hands of that science. In the meanwhile it is evident that unless the variation obtain encouragement from the environment no advance in type occurs. Now the land offers to an organism sufficiently evolved to benefit by it, opportunities the sea does not possess. First of these, undoubtedly, is the care it enables to be given to the young. To cast one’s brood upon the waters is not the best method of insuring its bringing up. There is too much of the uncertainties of wave and current to make the process a healthy one, and even when attached to rocks and seaweed, the attachment to a mother is to be preferred. Without a period of infancy, when the young is unable to do for itself, no great development is possible. In the only striking exception, the case of the whales, dolphins, and porpoises, size has probably counted for much in the matter, while the development of the cetaceans is far behind that of the majority of land mammals.

Change of place, not in distance, but in variety, is another factor. The sea is same as a habitat, one square mile of it being much like another, except for gradually changing temperature. The land, on the other hand, from its accidented surface, presents all manner of diversity in the conditions. And the more varied the conditions to which the organism is exposed, the greater its own complexity must be to enable it to meet them.

That the terrestrial stage of planetary development is subsequent to the terraqueous one, and must of necessity succeed it if the latter ever exist on a body, follows from the loss of internal heat on the one hand and from the kinetic theory of gases on the other. To which of the two to attribute the lion’s share in the business is matter for doubt; but that both must be concerned in it we may take for certain.

So long as the internal heat suffices to keep the body fluid, the liquid itself sees to it that all interstices are filled. As the heat dissipates, the body begins to solidify, starting with the crust. For cosmic purposes it undoubtedly still remains plastic, but cracks of relatively small size are both formed and persist. Into these the surface water seeps. With continued refrigeration the crust thickens, more cracks are opened and more water given lodgment within, to the impoverishment of the seas. The process would continue till the pressure of the crust itself rendered plastic all that lay below, beyond which, of course, no fissures could be formed. How competent to swallow all the seas such earth cuticle cracks may be we ignore; for we cannot be said to know much of the process. We can only infer that to a certain extent internal absorption of surface seas must mark a stage of the evolution by which a star becomes a world and then an inert mass, one of the dark bodies of which space is full.

Of the other means we know more. We are certain that it must take place, though we are in doubt as to the amount it has already accomplished. This method of depletion is by the departure of the water in the form of gas, in consequence of the molecular motions. If we knew the temperature and the age of Mars and also the amount of atmosphere originally surrounding it, we could possibly predicate its state. Reversely, we can infer something as to age and temperature from its present condition.