Chapter 3 What the rocks say: how geology and paleontology reveal the history of life
Darwin recognized that evolution required an old earth • Darwin argued that earth could be billions of years old • Disputed by Lord Kelvin – Proposed earth was no more than 20 million years old based on the temperature of rocks – Calculations later proven to be flawed
Radiometric dating estimates the age of the earth at 4.56 billion years old
Radiometric dating indicates that the earth is 4.6 billion years old
Fossils allow us to learn about extinct species • Morphology • Behavior • Development
Most organisms don’t fossilize
Occasionally soft tissues fossilize • Burgess shale – 505 million years ago – ~65,000 specimens – ~93 species
Fossils provide clues about behavior
Fossils provide clues about development
Scanning electron microscopy provides evidence of cellular structure • Structure of melanosomes suggests striking plumage
Cat scans help determine function of hadrosaur crest • Crest connected to nasal cavity – Sound generated by blowing air • Ears tuned to this frequency
Carbon isotopic signatures used to infer diet of early hominins • C 4 plants have higher C 13 than C 3 plants – C 13 /C 12 ratio used to infer types of plants eaten
History of life on earth revealed by fossil record
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