THE AGE OF THE EARTH.

Taranaki Daily News, 5 January 1922, Page 6

THE AGE OF THE EARTH.

“MODERATE MULTIPLE OF 1,000 MILLION YEARS.” London, Sept. 16, The age of the earth discussion on Tuesday attracted the largest and most representative audience one has seen, and some hundreds had to be turned away through lack of room. All the physicists, mathematicians, geologists, and zoologists were there, besides many of the chemist and stray members from other sections. Lord Rayleigh opened by stating that he had definite evidence to bring forward. He would not say that his answer was right, but he would not be giving it if he did not think it was. Thirty years ago Lord Kelvin said the earth was cooling at a rate which made it seem certain, “provided no new sources of heat were discovered,"’ that 20.000,000 years ago it was unfit for the existence of life. The same reasoning, with the same qualification, showed that in another 20,000.000 years the sun would no longer be a source of light and heat for its planets. The geologists and zoologists objected that the time was too short, but they had no very definite data to found their case on Within recent years the discovery of the release of intra-atomic energy by radioactive substances had put a a entirely new aspect on the question, at least as regards the earth. Uranium was changed through radium to lead by a long series of transformations, in which “chips” of helium were thrown off with enormous velocity producing heat as one of their results. Indeed the difficulty just now was to understand why th- earth should not be getting hotter instead of cooler, in view of the" quantity of uranium present in the earth’s crust.

AGE OF THE OLDEST ROCKS. How could the transformation of nra niuin into lead b«, made a clock for measuring past eras? The rate of the transformation per annum was accurately known. It was excessively small, only 1.22 x 10-10 of a given quantity per annum. If they took a mineral containing uranium lead and estimated the relative amounts of these substances present, they could calculate the time of the formation of the mineral in question. The result showed that the oldest or archean rocks had an antiquity of 925 million years. Similar evidence was got from the amount of helium present, if one allowed for its tendency to evaporeth-n and diffusion. If the same methods were used for rocks of more recent geological formation smaller results were naturally attained. On the whole physical chemistry confirmed geology in the sequences of strata it had accepted. For

example, iron ore from a certain eocene formation was found to b? 30 million years old. but the earth’s crust in some form or other was older than the oldest rocks, and from an estimation of the total quantities of uranium and lead present an- antiquity of something like 6,000 million years was probable. . Professor Sollas, the geologist, who followed, said that, like a “bloated capitalist” of time. Lord Rayleigh had aiven the geologists more millions of years than they knew what to do with; but Professor Gregory, also a geologist, warmly denied this, and would apparently be content to have still more. Professor Eddington added that stellar physics had something to say on the question of the duration of the suns heat, which had probably been maintained for a time long enough to cover the millions of years postulated by Lord Rayleigh. There was a group of variable <nant stars, the Cepheids. One of them, so large that it could fill the earth s orbit. had a period of 5 1-3 days, but was gradually slowing down, the rate of change being 1 per cent, in 58.000 years. This gave a change of density and through that a comparison with our sun as ft is now. We could safely credit the sun with a -past history as a heat and li'dit giving source of several thousand million years. Probably the variability of the Cepheid in question was due to the enormous alternate expansion and contraction on its part.