| OCR Text |
Show ESTIMATING AGE OF EARTH ! Geologists Have Differed Greatly at to the Time It Has Been In Existence. As long ago as I860 John Phillips, tho geologist, estimated that tho tlmo required for tho deposition of tho stratified stra-tified rocks lay botweon 38,000,000 and 9b,000,000 years. This was probably the only cstlmato prior to Kelvin's epoch-making paper of 1862. Slnco that time many estimates have neon made, varying all tho way from 17,000,-000 17,000,-000 years to 400,000,000 years. Kelvin wob tho first to discuss tho ago ot tho earth considered as a cooling body. In 1893 Clarence King Introduced the Important criterion ot tidal stability and reached the conclusion that 24,-000,000 24,-000,000 represented tho conditions. This result was adopted by Kelvin In 1897, and then ho placed tho limits as 20,000,000 and 40,000,000 years. Only Sir Oeorge Darwtn has discussed the age of tho earth from a purely astronomical astro-nomical point ot view. From his theory ot the earth-moon system he derived an estimate ot more than 60,000,000 ears, which for a long time stood between be-tween groups of higher and lower figures. fig-ures. J. Joly was tho first to baao estimates of tho ago "of tho earth, In 1899, on the sodium contained In tho ocean. Adopting the hypothesis that the sodium content of the ocean Is derived at a constant rato from that of tho rocks, he arrived at an age ot 80,000,000 or 90,000,000 years, and increased in-creased this by 10,000,000 in 1900. In 1909 Mr. Sollas made a searching Inquiry In-quiry Into this subject and placod the age ot the ocean at betwoon 80,000,000 and 160,000,000 years. |
