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Text File  |  1996-11-22  |  8KB  |  162 lines
  1.  
  2.                                GEOLOGIC TIME SCALE:
  3.                       FROM 4600 MILLION YEARS AGO TO PRESENT
  4.  
  5. millions
  6. of years
  7.   ago      era          period                          notes
  8.  
  9.    4600 ^  Precambrian  Precambrian                     The formation of the
  10.         |      .            .                           Earth's crust and the
  11.         |      .            .                           subsequent evolution of
  12.         |      .            .                           life
  13.         |
  14.    4550 +
  15.         |
  16.         \ (Note:  Precambrian era lasts from 4600 million years ago to 570
  17.         /  million years ago, a span of over four billion years.  A time-
  18.         \  line showing this would extend another 403 lines, or roughly 7
  19.         /  pages.)
  20.         |
  21.     600 +
  22.         |
  23.         |
  24.         |  Palaeozoic   Cambrian                        Marine animals with
  25.         |      .            .                           mineralized shells
  26.     550 +      .            .                           appear:  trilobites,
  27.         |      .            .                           echinoderms, brachio-
  28.         |                                               pods, molluscs,
  29.         |                                               primitive graptolites;
  30.         |                                               a variety of worms
  31.     500 +               Ordovician                      Graptolites dominant;
  32.         |                   .                           also trilobites, 
  33.         |                   .                           brachiopods, bryozoans,
  34.         |                   .                           gastropods, bivalves,
  35.         |                                               echinoids, crinoids,
  36.     450 +                                               cephalopods, and corals
  37.         |               Silurian                        Barchiopods, crinoids, 
  38.         |                   .                           corals, corals; prim-
  39.         |                   .                           itive fish
  40.         |                   .
  41.     400 +               Devonian (395)                  Corals, brachiopods,
  42.         |                   .                           ammonoids, crinoids;
  43.         |                   .                           fishes and early land
  44.         |                   .                           plants
  45.         |
  46.     350 +               Carboniferous (345)             Foraminiferans, corals,
  47.         |                   .                           bryozoans, brachiopods,
  48.         |                   .                           blastoids; seed ferns, 
  49.         |                   .                           lycopsids, and other 
  50.         |                                               plants; amphibians 
  51.     300 +                                               become more common
  52.         |               
  53.         |               Permian                         Trilobites extinct;
  54.         |                   .                           Amphibians and reptiles
  55.         |                   .                           dominant land animals;
  56.     250 +                   .                           gymnosperms dominant
  57.         |                                               plants
  58.         |  Mesozoic     Triassic                        Molluscs dominant
  59.         |      .            .                           invertebrates; reptiles
  60.         |      .            .                           dominant:  turtles,
  61.     200 +      .            .                           dinosaurs, ichthyosaurs
  62.         |               Jurassic                        Ferns, cycads, ginkgos,
  63.         |                   .                           rushes, conifers; ammo-
  64.         |                   .                           nites and other inver-
  65.         |                   .                           tebrates; pterosaurs,
  66.     150 +                                               _Archaeopteryx_ appears
  67.         |               Cretaceous (136)                Angiosperm plants;
  68.         |                   .                           Mesozoic reptiles peak
  69.         |                   .
  70.         |                   .
  71.     100 +
  72.         |
  73.         |
  74.         |  Cenozoic     Tertiary (65)                   Mass extinction:  dino-
  75.         |      .            .                           saurs, pterosaurs, and
  76.      50 +      .            .                           ammonites extinct; rise
  77.         |      .            .                           of modern animals;
  78.         |                                               shrubs, grasses, and
  79.         |                                               other flowering plants
  80.         |                                                   .
  81. PRESENT +               Quarternary (1.8)                   .
  82.         v
  83.  
  84.  
  85.                          INSET:  CENOZOIC ERA
  86.  
  87. millions
  88. of years
  89.   ago      era          period       epoch              notes
  90.  
  91.         ^
  92.         |
  93.      65 +  Cenozoic     Tertiary     Palaeocene         Mammals become abundant
  94.         |      .            .            .              after extinction of
  95.         |      .            .            .              dinosaurs and large
  96.         |      .            .            .              reptiles; by the
  97.         |                                               beginning of the Eocene
  98.      60 +                                               rodents and primates
  99.         |                                               have evolved
  100.         |
  101.         |
  102.         |
  103.      55 +
  104.         |                            Eocene             Mammals dominant:
  105.         |                                .              rodents, artiodactyls,
  106.         |                                .              carnivores, perisso-
  107.         |                                .              dactyls (including
  108.      50 +                                               horses); whales make
  109.         |                                               their first appearance
  110.         |
  111.         |
  112.         |
  113.      45 +
  114.         |
  115.         |
  116.         |
  117.         |
  118.      40 +
  119.         |
  120.         |                            Oligocene          Continued rise of 
  121.         |                                .              mammals:  pigs,
  122.         |                                .              rhinoceroses, and 
  123.      35 +                                .              tapirs make their
  124.         |                                               appearance
  125.         |
  126.         |
  127.         |
  128.      30 +
  129.         |
  130.         |
  131.         |
  132.         |                            Miocene            More and more modern
  133.      25 +                                .              mammals:  horses, dogs
  134.         |                                .              and bears, modern 
  135.         |                                .              whales, South American
  136.         |                                               monkeys; modern birds,
  137.         |                                               apes present in 
  138.      20 +                                               southern Europe, 
  139.         |                                               _Ramapithecus_ appears
  140.         |
  141.         |
  142.         |
  143.      15 +
  144.         |
  145.         |
  146.         |
  147.         |
  148.      10 +
  149.         |
  150.         |
  151.         |                            Pliocene           Mammals similar to 
  152.         |                                .              modern forms evolve;
  153.       5 +                                .              australopithecines
  154.         |                                .              appear, the forerunners
  155.         |                                               of humanity, appear
  156.         |               Quarternary  Pleistocene (1.8)  Ice ages; _Homo 
  157.         |                   .            .              sapiens_ evolves
  158. PRESENT +                   .        Holocene (0.01)    Human history
  159.         v
  160.  
  161.  
  162.