﻿AGE 
  OF 
  THE 
  EARTH 
  — 
  CHAMBERLIN 
  AND 
  OTHERS. 
  243 
  

  

  Sollas. 
  4 
  These 
  estimates 
  form 
  an 
  admirable 
  point 
  of 
  departure 
  for 
  

   this 
  discussion. 
  They 
  represent 
  the 
  mode 
  of 
  geologic 
  interpretation 
  

   that 
  has 
  been 
  most 
  current 
  until 
  recently 
  ; 
  they 
  typify 
  opinions 
  widely 
  

   held 
  by 
  the 
  conservative 
  school 
  of 
  geologists 
  ; 
  they 
  stand 
  out 
  in 
  con- 
  

   trast 
  to 
  the 
  views 
  of 
  the 
  new 
  school. 
  5 
  The 
  mean 
  of 
  the 
  four 
  esti- 
  

   mates, 
  on 
  the 
  basis 
  of 
  the 
  sediments, 
  was 
  90,000,000 
  years, 
  roundly 
  ; 
  

   on 
  the 
  basis 
  of 
  the 
  ocean, 
  95,000,000 
  years. 
  The 
  highest 
  individual 
  

   estimate 
  was 
  150,000,000 
  years; 
  the 
  lowest 
  70,000,000 
  years. 
  I 
  shall 
  

   not 
  deal 
  with 
  the 
  individual 
  estimates, 
  but 
  merely 
  with 
  their 
  mean 
  

   value, 
  and 
  with 
  that 
  only 
  as 
  representative. 
  

  

  My 
  discussion 
  can 
  not 
  be 
  specific 
  and 
  concrete 
  without 
  some 
  refer- 
  

   ence 
  to 
  views 
  in 
  other 
  fields. 
  My 
  colleagues 
  in 
  this 
  symposium 
  will 
  

   give 
  you 
  the 
  last 
  word 
  from 
  their 
  viewpoints, 
  and 
  if 
  I 
  could 
  follow 
  

   them 
  I 
  would 
  gladly 
  take 
  their 
  estimates 
  as 
  specifically 
  representa- 
  

   tive 
  in 
  their 
  several 
  lines. 
  In 
  lieu 
  of 
  this, 
  I 
  can 
  only 
  use 
  such 
  gen- 
  

   eral 
  views 
  as 
  are 
  current. 
  It 
  has 
  long 
  been 
  known 
  to 
  be 
  the 
  view 
  of 
  

   many 
  biologists 
  that 
  the 
  evolution 
  of 
  life 
  required 
  much 
  more 
  than 
  

   100,000,000 
  years. 
  It 
  is 
  also 
  well 
  known 
  that 
  most 
  estimates 
  based 
  on 
  

   radio-activity 
  greatly 
  exceed 
  this. 
  Astronomical 
  opinion 
  has 
  re- 
  

   cently 
  been 
  trending 
  toward 
  the 
  view 
  that 
  long 
  periods 
  are 
  neces- 
  

   sary 
  for 
  certain 
  typical 
  phases 
  of 
  celestial 
  evolution. 
  Perhaps 
  I 
  

   may 
  overstep 
  my 
  proper 
  limits 
  far 
  enough 
  to 
  say 
  that 
  I 
  have 
  re- 
  

   cently 
  tried 
  to 
  form 
  some 
  notion 
  of 
  the 
  time 
  required 
  for 
  the 
  gather- 
  

   ing 
  of 
  planetesimals 
  from 
  what 
  seemed 
  a 
  probable 
  distribution 
  into 
  

   the 
  collecting 
  planetary 
  nuclei, 
  and 
  found 
  a 
  period 
  of 
  the 
  order 
  of 
  

   two 
  or 
  three 
  billion 
  years 
  the 
  most 
  probable. 
  6 
  These 
  current 
  views 
  

   in 
  the 
  collateral 
  fields 
  warrant 
  me 
  in 
  assuming 
  that 
  there 
  is 
  a 
  wide 
  

   discrepancy 
  between 
  the 
  geological 
  estimates 
  just 
  cited 
  and 
  the 
  

   present 
  estimates 
  in 
  the 
  related 
  fields. 
  In 
  view 
  of 
  this 
  I 
  can 
  perhaps 
  

   serve 
  you 
  best 
  by 
  inquiring 
  whether 
  the 
  recent 
  additions 
  to 
  geologic 
  

   evidence 
  and 
  the 
  newer 
  modes 
  of 
  interpretation 
  mitigate 
  this 
  

   discrepancy 
  in 
  any 
  appreciable 
  measure. 
  Let 
  us 
  consider 
  first 
  what 
  

   the 
  newer 
  evidence 
  relative 
  to 
  the 
  sediments 
  has 
  to 
  say, 
  and 
  turn 
  

   later 
  to 
  the 
  solutions. 
  

  

  4 
  W. 
  J. 
  Sollas, 
  "Presidential 
  address," 
  Quart. 
  Jour. 
  Geol. 
  Soc, 
  vol. 
  65 
  (May, 
  1909), 
  

   Froc. 
  Geol. 
  Soc. 
  of 
  London., 
  sess., 
  1908—9, 
  pp. 
  1-cxxii. 
  

  

  8 
  It 
  is 
  not 
  practicable 
  to 
  summarise 
  the 
  time 
  estimates 
  of 
  the 
  newer 
  school 
  consistently 
  

   with 
  the 
  division 
  of 
  labor 
  adopted 
  In 
  this 
  symposium 
  since 
  they 
  are 
  composite, 
  embracing 
  

   organic, 
  astronomic, 
  and 
  radioactive 
  factors, 
  with 
  some 
  emphasis 
  on 
  the 
  last. 
  The 
  fol- 
  

   lowing 
  papers 
  of 
  this 
  class 
  may 
  be 
  taken 
  as 
  representative 
  : 
  J. 
  Joly, 
  " 
  Radioactivity 
  and 
  

   geology," 
  Van 
  Nostrand, 
  New 
  York 
  (1909), 
  pp. 
  233-251 
  ; 
  Arthur 
  Holmes, 
  " 
  The 
  age 
  of 
  the 
  

   earth," 
  Harper 
  Bros., 
  London 
  and 
  New 
  York 
  (1913), 
  pp. 
  1-196; 
  J. 
  Barrell, 
  "Rhythm 
  and 
  

   the 
  measurement 
  of 
  geological 
  time," 
  Bull. 
  Geol. 
  Soc. 
  Am., 
  vol. 
  28 
  (1917), 
  pp. 
  745-904; 
  

   T. 
  C. 
  Chamberlin, 
  " 
  Diastrophism 
  and 
  the 
  formative 
  processes," 
  XIII, 
  " 
  The 
  time 
  over 
  

   which 
  the 
  Ingathering 
  of 
  planetesimals 
  was 
  spread," 
  Jour. 
  Geol., 
  Vol. 
  XXVIII 
  (1920), 
  

   pp. 
  675-681. 
  

  

  • 
  Diatrophism 
  and 
  the 
  formative 
  processes, 
  XIII, 
  The 
  time 
  over 
  which 
  the 
  ingathering 
  

   of 
  the 
  planetesimals 
  was 
  spread, 
  T. 
  C. 
  Chamberlin, 
  Jour. 
  Geol., 
  Vol. 
  XXVIII 
  (1920), 
  pp. 
  

   675-681. 
  

  

  