HUMANITY'S SPAN

Evening Star, Issue 21091, 2 May 1932, Page 13

HUMANITY'S SPAN

HOW LONG WILL IT LAST? Although from time to time fears are expressed that this world of ours is nearing its end as a home for the human race, from a scientific point of view it is probable that man is still in his infancy. Life in some form or other lias already existed on this earth for more than a thousand million years, and for all we know it may continue for an equal length of time, writes Sir Richard Gregory, emeritus professor of astronomy at Queen’s College, London, in the ‘ Daily Herald.’ There is always, however, the chance of a physical accident bringing the earth, or at any rate human life, to an untimely end. Our solar system probably came into existence through a celestial collision, and a similar occurrence may well bring it to an end. There are substantial reasons for believing that the “ new stars ” which appear from time to time are caused by collisions in space. Whatever the truth, it is by no means impossible that the earth may one day become involved in a celestial collision of a similar kind. Our sun, with its planets, is moving into an unknown part of space at the rate of about 800,000 miles a day. Who knows whether some other non-luminous body or vast cloud of dark cosmic dust will not one day cross our path? We know that in certain parts of the sky there are “ curtains ” of obscuring matters which blot out whatever is behind them. In course of time the earth may encounter one of these dark aggregations of non-luminous material, and then the doom of this planet will be sealed. But Jong before we reached such a cloud of cosmic dust in our path eccentricities in the motions of the other planets would reveal our impending fate. As we approached the dark mass its force of gravitation would presently cause eruptions and tidal waves never before known. Shortly before the collision this force would become so great that the adjacent oceans would be drawn upwards in vast tides. They would overwhelm a largo part of the land, and oven the solid earth would become distorted. Apart from such a catastrophe, there is always the prospect of our being struck by a much smaller body, such as a comet, in Juno, 1921, the earth narrowly escaped such an encounter. A comet crossed its path only a few days before. More than once this earth has passed through the tail of a comet, but beyond an occasional display of shooting stars no one noticed anything unusual as the result. If, however, we happened to strike the head of a comet —and it is always possible for such a chance to occur—the effects would bo very different. That head may be anything from 500 miles to 2,000 miles in diameter, and the heat generated by collision with such a mass would be sufficient to destroy all forms of life on the earth and leave our world a waste of barren rock. The earth is of such an age that it has no doubt como into collision with comets more than once, and there is little doubt that similar collisions will take place. In addition to comets, the solar system contains vast numbers of meteors. They travel singly or in swarms, and continually register their existence as shooting stars and fireballs. Several millions of them cross tho earth’s path every day. Fortunately for us, most of them are burnt up in passing through our atmosphere, which acts like a torpedo net, but it occasionally happens that some larger one reaches the earth’s surface before this occurs. Meteors have devastated a large area of forest in Brazil. In 1908 thousands of tons of shooting stars swept many square miles of primeval forest in Siberia. In Northern Arizona is a crater three-quarters of a mile in diameter and 200yds deep. No doubt it mark:-; the spot where some huge meteorite fell. An encounter with a largo swarm of such bodies would denude the earth's surface and obliterate the human racx