The Press. SATURDAY, AUGUST 6, 1904. THE AGE OF THE HABITABLE GLOBE.

Press, Volume LXI, Issue 11955, 6 August 1904, Page 6

The Press. SATURDAY, AUGUST 6, 1904. THE AGE OF THE HABITABLE GLOBE.

There has long been a conflict of opinion between physicists and geologists as to the jrobable age of the habitable globe. Lord Kelvin and other mathematical physicists declare that life can only.have existed on the surface of the earth for a period of from ten to twenty millions of years. The biologists and geologist*, howerer, with Darwin, Wallace, and Lyell at their head, consider that from one hundred to two hundred million* of yean are required to account for th# formatica of the earth's ■.~ \ ■

crust and the development of life from tbe aniceba up to man. It has been rather a pretty quarrel, for both sidee hare been very positive in their statements, and discussion has tended rather to emphasise than reduce the amount of divergence of their opinions. It is a marked instance of a comparatively rare phenomenon—the attack of a scientific problem from two different standpoints with discordant results. Slaking all allowances for the poscibilities of error, the huge discrepancy shows that there it something fundamentally wrong with the data on one side or the other.

Geological time 1% measured chiefly by the rate of denudation and deposition of rocks. We know, for example, thai the sedimentary strata are some 200,000 feet thick, lliis doee not include immense deposit* which have been washed avj. Ihus the geological iratvey of Scotland estimates that the Cambrian strata have at one thne been separated from the Devonian and Silurian by deposits 15,000 feet in thickness, all ol3**M» have been removed by denudation, and other similar agencies. Now the rate at which denudation goes on at present may be taken as about one foot in 6000 yean. To have removed these 15,000 feet of rock would have, therefore, required ninety millions of jears. Such considerations as these led Sir Cheriea Lyell to postulate a> period of two hundred million years as the protable amount of time required for the formation of the earth's crust, with a minimum of one hundred millions of years. Some of the data employed are not very reliable, but the beat geological opinions tend to confirm this estimate. Now the conditions m to temperature under which life exist are fairly well known. All plants and animals are killed by ft temperature above that of boiling water. Hence the period of organic evolution can only have commenced, when tbe earth had cooled considerably under 212deg. F. Yet Darwin considered that two.hundred.mil* lions of years was little enough time- to allow for life to reach its present high state of development.

The physicists, however, refuse to allow, him anything like so long. Their arguments as to the age of the habitable globe are based chiefly (1) on the age of the eolar heat, (2) on tbe rate of cooling of the earth's interior. Tbe mm cannot go on for an. indefinite time radiating heat, to the earth, nor can it hare don© go for an indefinite time in the past. The rain of meteoric matter on its eurface can scarcely supply it with any consaderable amount of energy, and it is therefore generally supposed that its temperature js chiefly maintained by contraction- It was Helmholta who first of all pointed out tlits source of heat, and various • attempts have been made to find out tbe actual amount that reaches the earth, and hence the total. amount emitted. The results of these experiments are fairly harmonious, and from them can be calculated the amount of contraction of the

pun's diameter necewary to maintain tlie present rate of emission. The recolte of these calculations further led to the conclusion that the total duration of the son's heat can only be from ten to twenty millions of yearn It has also been ehown by Lord Kelvin and Tait (Thomson and Tait) that about "one hundred million " years after the earth wae a molten mass, "tbe gradually cooling due to radiation " from its surface would account for the " average temperature gradient of 1-50 deg. "F. per foot, observed to-day near th« "earth's" eurface."

Profeeor Rutherford, however, in hie recently published work on Radio-activity, has thrown a bombshell into the camp of the mathematical physicist*. It is evident that in radio-activity they have left on important factor out of their calculations. Radio-active emanations have been obtained (ram deep wells and from tie earth at Munich, Cambridge, New Haven (Cam.), Battaglia (Northern Italy); and, indeed, wherever they have been looked for. In many cases, it is clear that they were due to radioni itself. Now it can be shown that the presence of an almost incredibly minute quantity of radium in die earth'* crust—3ese than a billionth by volume or by weight—would be sufficient to compensate for the loss of heat from the earth by conduction. Similarly, it is ea«y to show that the presence of 3.6 grain* of radinui in each cubic metre of the tun's turface is sufficient to account for its present raid ol emkeion of energy. Xie> Lave no 'evidence at present, however, to show that radium exist* in the «un. Still, it seem* likely that the physicist* have altogether vtdtrafUnaUd the postibl* duration of life

on the earth'e surface, and that Lord Kelvin may hare also mnich under-estimated the sane- life when fce seid, "Aat for, tho "fmteiis we may tayi with eftt»l cer"tojnty, that iahabit«nt« of the «arUi Scan"not continue to enjoy the %hi «d beat "eseentJal to their life for many maUione "of yeawloogw, unlesi eoureee now xm"known to o» *re prepared in the great "storehotia** of cweUon." In the light of our present knowledge the last remark seesae almost prophetic. '