Anything Up to 5,000 Million Years: How Science Arrives at Estimates: Sediments, Ocean Salt, "Radio-Activity One of the best of a series of Joctures arranged by the Quest Society was given on Monday in the hall of the Royal Asiatic Society, by Dr. GB. Cressey, of the Shanghai College, on "How Old is 'Mother Earth?" Dr. H. Chatley presided and reminded those pres tent that' the next, leeture would be on April 30, when he will speak on "The Mystery of the Great Pyramids." In the course of his Interesting address, Dr. Cressey: said.
"The age of the earth is a problem which has engaged man's attention 1¢e the earliest times." Many peoples have had, legends about the origin of the world and the time since its creation, The Chaldeans fixed the age of the earth as two million years, while the Babylonians considered man to be half a million years old. The Persian sags limited the history of the death to 12,000 years, while the Hebrew chronology, as interpreted by Bishop Usher, fixed October 9, 5 the day of creation, avenge appeared at ten o'clock morning, On the other hand peoples in India have considered the earth as eternal. These early attempts to estimate the axe of the earth took the form of vague guesses which have no value today. Even at present any ate tempt to reconstruct pre-human history is regarded by some as bo-necessarily speculative, "The story of the earth ix written in the layers of sediments and the fossils which they contain. Those deposits form trustworthy aute-Biography of the earth evolution, and in them we may yead a most wonderful story, There can be no argument ubout the accuracy of this record, for it hax been written by the neth itself, The main task of geology ix to interpret the re-ori of the rocks.
The Sedimentary Record The first_method is based upon sntary record, This may the strictly geological method, The ago of the earth is fexevodingly great, however, that it is neceamry for us to prepare our minds for the figures.
The Yangtze River each year carries w great amount of sediment to the ocean, Tu addition to the mud transported in suspension there ie a great deal of material rolled along the bottom and even larger toad carried in. solution, Each ye r the Yangtze trans-rate of deposition at present, the figure daring most of earth' history was but a fraction, perhaps one-fifth or one-tenth. Thus, a 900 ft. well represents several ' times 90,000 years, probably a period of several hundred thousand years.
Tt we thus add together the maximum for each of the twenty' odd periods we find that in the course of earth history a total of 350,000 ft. of sediments have been deposited; in other words, about 70 miles, At the rate of one foot a century, it would require 35 mil-ion years for their accumulation. The evidence of she sedimentary method is: that the history of the earth represents many hundreds of millions of years. One estimate is 300, another 600, and others still longer, On any basis the earth exceedingly old, The sedimentary method cannot pretend to.be absolute, it is only relative; its value ies' in the indication of the great Tength of geologic time.
The Sodium Method The second method is somewhat more accurate: it is known as the sodium method, or the salt method. Each year the rivers transfer great quantity of rock matter solution from the lands to the eoans. On the basis of many analysis, this chemical lod of the world's rivers is fairly well Known. It ix believed that in the beginning the oceans were fresh and that all the salt has been added in this way. Over 200 years ago was suggested by Bailey, then Royal Astronomer of England, that here was a clue to the age of the earth, The problem may be expressed graphically as follows total sodium in the oceans by. the annual sodium in equals the age of the ocean, This of course is not the age of the earth, but only the period since water began to accumulate, but far as geology is concerned the two are closely related. The amount of sodium in the oceans is estimated to bbe 1441:80,600,000,000,000 tons, while the rivers annually contribute 142.- 521,000 tons. When these figures are divided the result is just about years. This again is only a minimum figure, The third method ix the most re-Hable and ix based upon radio-n tivity. In 1896 the discovery was made that when a certain" substance was left next to a photographic plate wrapped in black Paper, something happened to the age quantities of lead and uranium in the rocks of the earth's crust. On this basis the figure is less than 3,000 million years. Stil! other methods are based "upon astronomic considerations and nood not be discussed. In general-they assign a figure of from 2,000 to 5,000 million years as the age of the planet. Geologic time may be taken as 1,500 million years; this figure cannot be presented as strictly accurate, for the error may be 20 per cent. or more.
'Such figures are dazzling and pass all human comprehension. Only by a detailed study of the events of earth evolution, both physical and biological, can' we ap-Preciate such a vast duration of time. If, for the sake of comparative values, we compress all of earth history into the period of a day, one minute equals a milli yeats, The Archeozoie and Proterozoie eras, shrouded in the darkness of night, lasted fifteen hours. The Cambrian. period, which marks the beginning of clearly recorded history, commenced about nine hours ago. The first land vegete. tion appeared in the Devonian, about six hours ago. Dinosaurs raled the earth for an hour about two hours ago. Man has been on the earth but one minute. Sine the last glaciation but two seconds have elapsed. Civilization has all Jdeveloped within half a second, while the Han dynasty was but one-eighth of a second ago, How shall we compare one lifetime or even one century with the vast ness of time?
Text read from the printed page and cleaned; old type leaves the occasional error.