MOTHER EARTH'S AGE.

Auckland Star, Volume LXII, Issue 305, 26 December 1931, Page 10

MOTHER EARTH'S AGE.

WRAPPED IN MYSTERY.

THE BASIS OF ESTIMATES

RADIO-ACTIVE DISINTEGRATION.

(From Our Special' Correspondent.)

WASHINGTON, November 20.

Mother Earth refused to tell her age

She is at least. 1,000,000.000 years old, and she may have reached the ripe old age of 3,000,000,000, but,-she cannot be tricked- into admitting the -number of birthdays, she has. known. .:' •.''.

Such is the. conclusion from- the most exhaustive application ever made of all known methods -for' estimating' the age of the world, the results of which have just been published by the " National Research Council. The above estimates were reached from a world-wide survey of radio-active disintegration, wliich' all the experts agreed was the best measuring stick, conductedby the British geologist, Arthur Holmes.

The method is based on the fact that certain rare elements, especially uranium and thorium, disintegrate spontaneously at. constant, determinable rates and change into lead. If it could be assumed that they were present at the beginning of tinvj the amount of lead associated with them would reveal accurately the age of the earth.

The oldest uranium-bearing rocks Dr. Holmes could find were some from the Black Hills of South Dakota, and from the province of Carelia, in Russia.. .The former showed an age of ; 1,400,000,000 years. The lead, associated . with the latter indicated 1,852,000,000 years, but the results were.not quite so,'.reliable. There is evidence that in .both: ; cases these rocks have intruded into still'older rocks which are. not * subject tip measurable atomic disintegration. '.. ■ \ .■ "We can still find," Dr. Holmes says, "no trace of a beginning. We.can.be sure that the earth is older than the oldest known rocks,", and therefore considerably older, than the oldest granitic intrusions. Before the oldest granites were intruded • into the earth's crust there was at least one' cycle of denudation and deposits" of the sedimentation being represented by the rocks into which the. granites; Were injected.". '.*:.< • ■'■ ".;-:;•'.. ■■■;':'} %' ' : "■'■ Thus, he holds,, to'the 1,160,000,600 i years of the South Dakota "rocks must! be added at least yearfeio.; account for the formation of' the .still' older rocks: . "•'■■"'•'•'; }i\ 1,600,000,000 is Minimum. ■■ _\-;. ; < But, Dr. Holmes stresses, this 1,600,000,000 years is very close to the minimum. Taking the average proportion of lead in igneous rocks, or those rocks which cooled from a molten state and probably were volcanic lava in the beginning, and assuming that it all came from radio-active disintegration the; world over, then the world's age. would: be;.close to 3,700,000,000 years. Eight here comes the. extreme difficulty; of: telling.:the. earth's age;> . :..-vi #}J;.'.'-- .?'■•:•. \ .'; There . are~'•. two of;'. lead and . ore lead; 1 / 'They' 1 differ in atomic weight. The the lead of; commierce,. could '-'■ riot. haVe] been derived, from atomic ■disintegratipftij But some of.it is found diffused" thVougfo; igneous rocks';:. The "rock*'?leadvfs/deajl* Uranium and thorium; When -this, alonej is> '.considered, on a- conservative Ae'sjti-i mate the figure 'is reduced ; to labovttt 3,000,000,000 years. Further research; ■ id- -expected -to make mOre'reductions/ but the geopliysicist rests on the conclusion that the earth is.betweeri : 000,000 and'.3,000,000,000 years'tild.: •An -important check on time/ it is. pointed out in. the report, comes• from the • discovery off the ' still ' mysterious phenomena of pleochroic halos.': ''These are ; Small, halo-like effects/ found in rocks which result from. \thg.; shooting out of. helium atoms' ..from tiny,' em< bedded pockets of radioactive material." They change the coloiu- of ing rock - as..far. las,.■ they t can,, penetrated While the interpretation ,of . is very obscure, Dr. Holmes explains; thev show beyond much doubt -that the fate of disintegration was the same 500,000,000 years ago as to-day. Most Puzzling Question. The age of the earth, it is pointed out in the National Research Council report, is one of the-most puzzling and.disputed questions in. science. Before, the dis : covery of radio-activity all authorities agreed that, estimating from the rate of cooling, the accumulation of salt in the sea, and the distance of the earth from the moon, the earth was between 20,000,000 and 90,000,000 years old. This was not enough time for the process of evolution to have taken place, even if life were coeval with the. earth itself. With the discovery of radio-activity In rocks' the estimates jumped . enormously, even to as high as 11,000,000,000 years. The value of the new method was'increased by theoretical considerations which showed that uranium, the heaviest of all the elements, must have been present from the beginning as part of the original material of the earth torn from the sun. •

But even with such an accurate hourglass there was little agreement as to how it should be read. The National Research Council Committee, headed by Prof. Adolph Knopf, set to work to accumulate all the available evidence. Reports of experts on the age of the earth as indicated by the depth of sedi-, mentary rocks formed through the ages, the salinity of the sea and astronomical considerations also are included. These are considered far less reliable clocks of the eons than radioactive disintegration—(N.A.N.A.)