﻿ORIGIN 
  OF 
  THE 
  EARTH 
  AND 
  ITS 
  CRUST 
  115 
  

  

  The 
  earth 
  Is 
  to 
  man, 
  one 
  of 
  the 
  two 
  most 
  important 
  members 
  

   of 
  a 
  group 
  of 
  celestial 
  bodies 
  held 
  in 
  relation 
  to 
  each 
  other 
  by 
  

   gravitation, 
  which 
  we 
  call 
  the 
  solar 
  system. 
  The 
  center 
  of 
  

   this 
  system 
  is 
  the 
  sun, 
  about 
  which 
  revolve 
  the 
  planets 
  with 
  

   their 
  satellites 
  and 
  the 
  planetoids, 
  and 
  without 
  which 
  as 
  a 
  source 
  

   of 
  light 
  and 
  heat, 
  no 
  life 
  could 
  exist 
  on 
  earth. 
  

  

  To 
  explain 
  the 
  origin 
  of 
  the 
  solar 
  system 
  the 
  Nebular 
  hypothesis^ 
  

   was 
  suggested 
  by 
  Swedenborg 
  and 
  Kant 
  and 
  elaborated 
  by 
  La- 
  

   place. 
  Although 
  not 
  completely 
  proven 
  it 
  is 
  highly 
  plausible, 
  

   and 
  answers 
  most 
  of 
  the 
  conditions. 
  According 
  to 
  this 
  hypothe- 
  

   sis 
  our 
  solar 
  sj^stem 
  originated 
  as 
  a 
  vast 
  nebula, 
  similar 
  to 
  

   nebulae 
  which 
  now 
  exist, 
  in 
  the 
  form 
  of 
  an 
  immense 
  volume 
  of 
  

   incandescent 
  gas 
  rotating 
  in 
  space 
  from 
  west 
  to 
  east, 
  of 
  which 
  

   the 
  limits 
  extended 
  beyond 
  those 
  of 
  the 
  present 
  solar 
  system 
  

   which 
  is 
  about 
  5,500 
  millions 
  of 
  miles 
  in 
  diameter. 
  

  

  As 
  this 
  mass 
  slowly 
  parted 
  with 
  its 
  heat 
  and 
  contracted 
  in 
  

   obedience 
  to 
  physical 
  laws, 
  its 
  velocity 
  of 
  rotation 
  would 
  increase 
  

   and 
  in 
  the 
  peripheral 
  or 
  outer 
  portion 
  the 
  centrifugal 
  force 
  would 
  

   overcome 
  the 
  attraction 
  toward 
  the 
  center, 
  causing 
  it 
  to 
  separate 
  

   from 
  the 
  central 
  portion 
  in 
  the 
  form 
  of 
  a 
  ring. 
  This 
  ring 
  through 
  

   unequal 
  condensation 
  would 
  subsequently 
  be 
  broken, 
  its 
  frag- 
  

   ments 
  uniting 
  by 
  gravitation 
  into 
  a 
  body 
  revolving 
  about 
  the 
  

   nucleus 
  and 
  ultimately 
  forming 
  a 
  planet 
  or 
  in 
  one 
  instance 
  a 
  

   zone 
  of 
  small 
  planets, 
  that 
  of 
  the 
  planetoids 
  or 
  asteroids. 
  This 
  

   process 
  is 
  supposed 
  to 
  have 
  continued 
  until 
  the 
  various 
  mem- 
  

   bers 
  'of 
  the 
  system 
  were 
  set 
  free; 
  the 
  remnant 
  of 
  the 
  much 
  dimin- 
  

   ished 
  but 
  still 
  intensely 
  heated 
  nucleus 
  remaining 
  as 
  our 
  sun 
  

   which 
  now 
  has 
  a 
  diameter 
  of 
  860,000 
  miles. 
  The 
  primary 
  rings 
  

   after 
  condensing 
  into 
  planets 
  are 
  believed 
  to 
  have 
  formed 
  second- 
  

   ary 
  rings 
  Y/hich 
  subsequently 
  broke 
  and 
  became 
  satellites, 
  except 
  

   in 
  the 
  case 
  of 
  Saturn 
  which 
  still 
  retains 
  two 
  rings. 
  

  

  Inasmuch 
  as 
  some 
  of 
  the 
  planets 
  near 
  the 
  sun 
  are 
  denser 
  than 
  

   those 
  more 
  distant, 
  it 
  has 
  been 
  suggested 
  that 
  in 
  the 
  rotation 
  

   of 
  the 
  primal 
  nebula 
  its 
  components 
  arranged 
  themselves 
  in 
  lay- 
  

  

  flSee 
  Young, 
  General 
  Astronomy, 
  p. 
  515-25. 
  

  

  