| Show 0 THE casual observer the mountains seem a type of eternity we naturally of the ellla as ever lasting A favorite mode of expressing future eter alty Is to say as long as the world en dureth even to the astronomer with his most perfected instruments for measurement of both space and force no varla alon in the diameter of either the earth or the sun has been discovered this however Is not because no changes are taking place but because they are so slow and man so short lived that they do not make themselves percept elble to our dull senses la reality there Is no absolute uniformity in na ture everything la changing tomor to mor TOW will not be like today to day and today to day Js not like yesterday what were the conditions a million years ago and what will be a million years hence are largely matters of conjecture still we have data enough to make interesting it not perfectly con elusive it Is estimated that if all the matter in the solar estem had been moving from the utmost bounds of space to wards the center of the sun it would heat at the present rate tor only 18 years but it Is able that formerly the radiation of the THE Y hac ha sun when it filled much larger space than now was greater than at present it Is a rather startling fact that it the suns heat were increased by much more than one half it would boll away all the water on the globe As water Is necessary to life on the globe prof newcomb our great authority at washington thinks that the balance ot causes which would result n the aun radiating heat just fast enough to preserve the earth in its present state has probably not existed more than years and that this la therefore near the extreme limit of time that we can suppose water to have existed on the earth in the fluid state but though the mathematicians insist that some such limit as or years must be placed upon the existence of even the lowest forms of life on the earth geologists atall contend for a longer lease of time reasoning from the known rato at which forms 0 life change darwin and lyell assumed that it must have been on the earth for many hundred million years darwin indeed in his earlier editions of the origin of species speaks of yeara aa a mere trifle of geologic time but the geologists of the present day are more modest in their demands and would ap patently ly be satisfied with or twice that num her of years alfred russell wallace however from geological evidence calculates that 30 ears Is all that need be demanded for the facts of geology wallaces estimate la an interesting one taking the thickness of the sedimentary rocks at feet which s an extreme estimate and reckoning the coast line of the globe at miles and that the sediment brought into the sea la deposited on an average or a belt 30 a tl miles wide he ands that at the present rate the total thickness of rocks would be formed within the above mentioned length of time for at the present rate of ero slon of the continents the whole land surface of the earth Is lowered one toot in 3 years and the sediment deposited along the shores of the continents one foot fram square miles the land surface of the earth Is equal to 19 feet deposited in 3 years over the belt stretching 30 miles out from miles of shore line divided by 19 multiplied by equals 28 such Is the reduction to the age of the world made by the more recent investigations both of astronomers and geologists assuming the truth of the nebular hypothesis po thesis prof george II 11 darwin obtained results remark ably similar from calculations concerning the relations of the moon to the earth the moon produces tides upon the earth and coner the earth must produce i tides upon the moon As was long ago shown these tides retard the dally motion of the revolution of these bodies the tides are equivalent to a wave on the earth about three feet high striking twice a day on the eastern shore of the continents this has the same effect as a brake on a wheel and imperceptibly but surely regards retards its motion As the moon Is much smaller than the earth and benco has less momentum its motion baa been af fectea much more by its tides than has that of the earth whereas the moon once resolved on its axis very rapidly it now requires a whole month to revolve and so keeps the same face toward the earth all the time it Is estimated that to produce the present amount of heat the diameter of the sun must contract feet per year or a mile in 25 years tour miles a century though this is too small an amount to hare been noted by any present means of measurement since accurate observations began to be made it Is by no means an cant amount dy darwin s calculation it was shown that gormerly tor merly the earth revolved on its axis once every eight hours but was reduced to its present rate by the same process that has reduced the moon at the time when the moon and earth were revolving so rapidly they were touch nearer to each other than now indeed so near that the tides they produced on each other were many almea as great as those now produced so great indeed waa the tidal wave which then rolled over the world that it la hardly possible to suppose that any form of life could have endured the con going further mr darwin proved that the moon was originally thrown off from the mass of earth by the in creased centrifugal motion of the contracting sphere of the earth as water Is thrown of from a grindstone furthermore by his calculations of the retarding influx ence of tho tides he proves that this could not have occurred less than nor more than years ago all geologic time therefore must be brought much within these limits for after the birth of the moon an immensely long period must have elapsed before the conditions were such upon the earth that life could have endured them so that his calculations agree in remarkable manner with those of mr wallace and of prof newcomb but years Is a long time and slowly work i ing causes produce immense results within that period As darwin remarks few 0 us know what a million really means take a narrow strip of paper 83 feet tour inches in length and stretch it along the wall of a large hall then mark off at one end the tenth of an inch this tenth of an inch will represent yeara and the strip a million years bearing this in mind we shall appreciate the following calculations concerning the great length of the geological periods even on mr wallace a estimate of the total length of geological time and they will seem sufficiently long or all necessary purposes dana estimates the ratio for the paleozoic meso and cenozoic periods to be 12 3 I 1 that Is cenozoic times the time since the beginning of the tertiary period Is one sixteenth of the whole or about years mesozoic time the age of the prevalence of reptiles would be about thice of the time or years alle time be about three fourths of the time that Is about 20 years if however we should be compelled to accept the calculations of prof newcomb these would have to be reduced more than one half but the accumulating facts concerning the rapidity of the action of present geological forces seem to ba pointing toward these lower estimates and to make it entirely credible that the earth has not been suitable tor the existence of man tor very many thousand yeara the loose estimate in which hundreds ot thousands of years are assigned to the existence ot the human race take little account of the real facts which are coming to light |
