The science of life : fully illustrated in tone and line and including many diagrams

INTRODUCTION

of a mile, to judge by the length of line a harpooned individual will reel out. But this depth is not equal to the height of such a winter resort as Arosa

Anything normally enclosing air or other gas, such as the strands of a rope or a piece of woolly fabric, is flattened out at great depths. If a ship’s hawser, says Professor J. Arthur Thomson—a hempen hawser, of course, is meant—is sunk to the depths of a couple of thousand fathoms, it is squeezed to less than the diameter of one’s wrist, and a piece of wood that has gone down so far will no longer float. Whatever lives at great depths—if it contains air or gas—must have its internal pressures as great as those about it.

Oceanographic exploration shows us that there is a definite zoning of life in the abyss, the creatures of the deeper levels being adapted to the peculiar conditions of their particular level.- They can no more come up than the surface life can go down—until it dies and drifts slowly to be eaten by the inhabitants of the lower darkness. Sometimes, however, some of the deep sea fishes fall upward. Many of them, like their surface kindred, have swimming bladders to accommodate themselves to varying levels. These bladders contain gas under enormous pressure. If one of the abyssal fishes rises too high in pursuit of its prey, the gas in its bladder may expand out of control of the muscles. The fish can no longer go down, but continues to rise helplessly, and as it rises to levels of less and less pressure, the expansive force of the gas within is less and less restrained, until at last the creature rushes up to the surface and arrives there distended or burst and dead.

The ocean at its deepest goes down perhaps for seven miles. Life, therefore, so far as we know, is confined to a layer of air and a layer of water, having a total thickness of less than fourteen miles, on this comparatively small planet Earth, and no one single form of life is able to span even these petty limits. Man’s vertical range seems to be as great as any creature’s and it is no more than eight miles. In all the wilderness of space outside this double film there are only the very faintest suggestions of the possible occurrence of life or of any processes parallel with and comparable to life.

§ 4 Is there Extra-terrestrial Life ? Speculation about life in extra-terrestrial space has occupied itself mainly in a search 8

for conditions similar to those recognized as the limiting conditions of life upon earth. Something like a wetter, hotter parallel to earthly conditions may be found upon the surface of the planet Venus, but the atmosphere of that planet is so continuously clouded, that it is impossible to obtain any confirmatory glimpses of vegetation or other living stuff. Slight changes of tint have been observed upon the surface of the moon and might just possibly be due to a transitory growth of plant-like organisms during the long sunlit day of that satellite. Mars displays rectilinear double markings, the “ canals,’ so unlike any other natural fissures in their straightness, that they have been ascribed to the engineering of intelligent beings, and there are also changes of colour upon the Martian surface that may be caused by the growth and ripening of irrigated crops. Mars has snow-caps which expand and contract as the Martian winter comes on and gives place to the Martian summer, and the canals may conceivably distribute the thawing water.

But ifindeed there are living things upon these other members of our solar system, they must be profoundly different in many ways from terrestrial life. It is doubtful if they could be transferred to terrestrial conditions and live, or if much or any terrestrial life could be transplanted to and acclimatized on the moon or Mars. The mass of Mars and still more so the mass of the moon is much less than that of the earth, the gravitational energy at the surface of either planet would be less, the atmospheric pressure would be much less, on the almost entirely airless moon it would be practically nil, and so the weight of a living body and of its parts and fluids would be much less there and the pressure on its surfaces very much less. ‘The lungs of a terrestrial animal would be unable to get air enough to breathe, the gases dissolved in the fluids of the body would effervesce and expand and blow out all its closed cavities, our joints would lock, the heart would drive the blood through the membranes that are sufficient to contain it on earth, and we should bleed in our lungs, in our throats, eyes, ears, and be choked with blood. On the other hand, a man reconstructed to walk on Mars would be crushed to death by his own weight on the earth. Life on Mars would have to be so different in its character from the life we know, that one would almost need another word for it. If we called terrestrial life Alpha life, we might call the life-parallel