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.