﻿AGE 
  OF 
  THE 
  EARTH 
  CHAMBERLIN 
  AND 
  OTHERS. 
  271 
  

  

  waves, 
  and 
  measurements 
  of 
  the 
  rigidity 
  of 
  the 
  earth 
  by 
  various 
  

   methods, 
  and 
  more 
  particularly 
  by 
  that 
  lately 
  developed 
  at 
  Chicago 
  

   by 
  Michelson 
  and 
  his 
  colleagues. 
  From 
  these 
  phenomena 
  we 
  know 
  

   with 
  fair 
  certainty 
  that 
  the 
  earth 
  behaves 
  mechanically 
  like 
  a 
  solid 
  

   body 
  which 
  has 
  approximately 
  the 
  rigidity 
  of 
  steel. 
  It 
  is 
  sometimes 
  

   assumed 
  that 
  this 
  shows 
  that 
  the 
  interior 
  of 
  the 
  earth 
  consists 
  of 
  

   matter 
  which 
  under 
  surface 
  conditions 
  of 
  pressure 
  would 
  be 
  solid. 
  

   Unfortunately 
  the 
  argument 
  is 
  doubtful, 
  because 
  we 
  know 
  nothing 
  

   of 
  the 
  condition 
  of 
  matter 
  under 
  the 
  pressures 
  which 
  it 
  experiences 
  

   at 
  depths 
  of 
  100 
  miles 
  or 
  more 
  below 
  the 
  surface 
  of 
  the 
  earth. 
  

   It 
  is, 
  therefore, 
  impossible 
  to 
  argue 
  with 
  any 
  security 
  concern- 
  

   ing 
  the 
  temperature 
  conditions 
  in 
  the 
  interior 
  of 
  the 
  earth 
  from 
  

   these 
  observational 
  data. 
  Lately, 
  Jeffreys 
  has 
  shown 
  that 
  under 
  

   almost 
  any 
  theory 
  of 
  evolution 
  the 
  earth 
  must 
  at 
  one 
  time 
  have 
  

   been 
  sufficiently 
  hot 
  so 
  that 
  all 
  its 
  materials 
  were 
  in 
  a 
  liquid 
  state, 
  

   understanding 
  by 
  this 
  latter 
  phrase, 
  a 
  state 
  liquid 
  under 
  surface 
  

   conditions 
  of 
  pressure. 
  

  

  Thus 
  the 
  astronomical 
  evidence 
  which 
  can 
  be 
  furnished 
  as 
  to 
  the 
  

   age 
  of 
  the 
  earth 
  is 
  practically 
  nil, 
  and 
  one 
  must 
  turn 
  to 
  methods 
  out- 
  

   side 
  the 
  range 
  of 
  the 
  astronomer's 
  work. 
  

  

  A 
  further 
  difficulty 
  may 
  be 
  mentioned. 
  Evidence 
  is 
  accumulating 
  

   that 
  there 
  is 
  widely 
  extended 
  diffuse 
  matter 
  in 
  space, 
  some 
  of 
  which 
  

   is 
  visible 
  and 
  some 
  of 
  which 
  is 
  only 
  evident 
  on 
  account 
  of 
  the 
  

   obscuration 
  of 
  light 
  which 
  it 
  causes. 
  It 
  therefore 
  seems 
  highly 
  prob- 
  

   able 
  that 
  the 
  solar 
  system 
  in 
  the 
  course 
  of 
  several 
  hundred 
  million 
  

   years 
  may 
  have 
  passed 
  through 
  one 
  or 
  several 
  such 
  clouds. 
  These 
  

   would 
  have 
  effects, 
  which 
  from 
  theory 
  are 
  well 
  known, 
  such 
  as 
  

   diminishing 
  the 
  mean 
  distances 
  of 
  the 
  planets 
  from 
  the 
  sun, 
  the 
  cir- 
  

   cularization 
  of 
  their 
  orbits, 
  possible 
  changes 
  in 
  the 
  total 
  angular 
  mo- 
  

   mentum 
  of 
  the 
  system, 
  and 
  other 
  effects, 
  such 
  as 
  the 
  possible 
  forma- 
  

   tion 
  of 
  comets 
  and 
  the 
  production 
  of 
  glacial 
  and 
  interglacial 
  periods. 
  

   At 
  present, 
  however, 
  the 
  consequences 
  of 
  this 
  hypothesis 
  are 
  still 
  in 
  

   the 
  range 
  of 
  speculation 
  and 
  need 
  to 
  be 
  worked 
  out 
  in 
  considerable 
  

   detail 
  before 
  any 
  arguments 
  can 
  be 
  built 
  on 
  it. 
  It 
  may, 
  however, 
  be 
  

   stated 
  that 
  such 
  a 
  hypothesis 
  would 
  have 
  the 
  general 
  tendency 
  of 
  

   increasing 
  the 
  age 
  of 
  the 
  earth 
  as 
  estimated 
  from 
  other 
  sources. 
  

  

  THE 
  RADIOACTIVE 
  POINT 
  OF 
  VIEW. 
  

  

  By 
  William 
  Dcanh, 
  

   Harvard 
  University. 
  

  

  In 
  estimating 
  the 
  age 
  of 
  the 
  earth 
  one 
  should 
  measure 
  the 
  time 
  

   that 
  has 
  elapsed 
  by 
  some 
  process 
  in 
  nature 
  that 
  takes 
  place 
  in 
  one 
  

   direction 
  only 
  and 
  that 
  does 
  not 
  change 
  its 
  rate 
  when 
  conditions 
  

   (temperature, 
  pressure, 
  etc.) 
  alter. 
  In 
  most 
  of 
  the 
  estimates 
  of 
  

  

  