Reading 7

This passage comes from a book titled Finding Your Inner Fish by Neil Shubin (© 2008 Neil Shubin).

  1. That a column of rocks has a
  2. progression of fossil species
  3. probably comes as no surprise. Less
  4. obvious is that we can make detailed
  5. predictions about what the species in
  6. each layer might actually look like by
  7. comparing them with the species of
  8. animals that are alive today; this
  9. information helps us to predict the
  10. kinds of fossils we will find in ancient
  11. rock layers. In fact, the fossil
  12. sequences in the world’s rocks can
  13. be predicted by comparing ourselves
  14. with the animals at our local zoo
  15. or aquarium.
  16. How can a walk through the zoo help
  17. us predict where we should look in
  18. the rocks to find important fossils?
  19. A zoo offers a great variety of
  20. creatures that are all distinct in many
  21. ways. To pull off our prediction,
  22. we need to focus on what creatures
  23. share. We can then use the features
  24. common to all species to identify
  25. groups of creatures with similar
  26. traits. All the living things can be
  27. organized and arranged like a set
  28. of Russian nesting dolls, with smaller
  29. groups of animals comprised in
  30. bigger groups of animals. When we
  31. do this, we discover something
  32. very fundamental about nature.
  33. Every species in the zoo and the
  34. aquarium has a head and two eyes.
  35. Call these species “Everythings.”
  36. A subset of the creatures with a
  37. head and two eyes has limbs. Call
  38. the limbed species “Everythings
  39. with limbs.” A subset of these
  40. headed and limbed creatures has
  41. a huge brain, walks on two feet,
  42. and speaks. That subset is us,
  43. humans. We could, of course,
  44. use this way of categorizing
  45. things to make many more
  46. subsets, but even this threefold
  47. division has predictive power.
  48. The fossils inside the rocks of the
  49. world generally follow this order,
  50. and we can put it to use in designed
  51. new expeditions. To use the
  52. example above, the first member of
  53. the group “Everythings,” a creature
  54. with a head and two eyes, is found in
  55. the fossil record well before
  56. “Everythings with limbs.” More
  57. precisely, the first fish
  58. (a card-carrying member of the
  59. “Everythings”) appears before the
  60. first amphibian (an “Everything with
  61. limbs”). Obviously, we refine this by
  62. looking at more kinds of animals and
  63. many more characteristics that
  64. groups of them share, as well as by
  65. assessing the actual age of the
  66. rocks themselves.
  67. Besides helping us refine the
  68. groupings of life, hundreds of years
  69. of fossil collection have produced a
  70. vast library, or catalogue, of the ages
  71. of the earth and the life on it. We can
  72. now identify general time periods
  73. when major changes occurred.
  74. Interested in the origin of mammals?
  75. Go to rocks from the period called
  76. the Early Mesozoic; geochemistry
  77. tells us that these rocks are likely
  78. about 210 million years old.
  79. Interested in the origin of primates?
  80. Go higher in the rock column, to the
  81. Cretaceous period, where rocks are
  82. about 80 million years old.
  83. The order of fossils in the world’s
  84. rocks is powerful evidence of our
  85. connections to the rest of life.
  86. If, digging in 600-million-
  87. year-old rocks, we found the
  88. earliest jellyfish lying next to the
  89. skeleton of a woodchuck, then we
  90. would have to rewrite our texts.
  91. That woodchuck would have
  92. appeared earlier in the fossil record
  93. than the first mammal, reptile, or
  94. even fish – before even the first
  95. worm. Moreover, our ancient
  96. woodchuck would tell us that much
  97. of what we think we know about the
  98. history of the earth and life on it is
  99. wrong. Despite more than 150 years
  100. of people looking for fossils—on
  101. every continent of earth and in
  102. virtually every rock layer that is
  103. accessible—this observation has
  104. never been made.