Slide 1Darwin recognized that evolution required an old earthSlide 3Fossils allow us to learn about extinct speciesMost organisms don’t fossilizeOccasionally soft tissues fossilizeFossils provide clues about behaviorFossils provide clues about developmentSlide 9Cat scans help determine function of hadrosaur crestBiomarkers reveal traces of lifeCarbon isotopic signatures used to infer diet of early homininsKey ConceptsScientists search for evidence of life in old rocksEarliest signs of lifeKey ConceptsHow do early organisms fit in the tree of life?Slide 18Slide 191/12/13Chapter 3What the rocks say: how geology and paleontology reveal the history of life1/12/13Darwin 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 flawed1/12/13Radiometric dating indicates that the earth is 4.6 billion years old1/12/13Fossils allow us to learn about extinct species•Morphology•Behavior•Development1/12/13Most organisms don’t fossilize1/12/13Occasionally soft tissues fossilize•Burgess shale–505 million years ago–~65,000 specimens–~93 species1/12/13Fossils provide clues about behavior1/12/13Fossils provide clues about development1/12/13Scanning electron microscopy provides evidence of cellular structure•Structure of melanosomes suggests striking plumage1/12/13Cat scans help determine function of hadrosaur crest•Crest connected to nasal cavity–Sound generated by blowing air •Ears tuned to this frequency1/12/13Biomarkers reveal traces of life•Biomarker: distinctive molecules only produced through biological activityEnzymatic reaction only carried out by purple sulphur bacteria1/12/13Carbon isotopic signatures used to infer diet of early hominins•C4 plants have lower C13 than C3 plants–C13/C14 ratio used to infer types of plants eaten1/12/13Key Concepts•Technology provides insights into morphology and behavior of extinct species•Biomarkers reveal information about the history of life1/12/13Scientists search for evidence of life in old rocks•Earliest life unlikely to be preserved in fossils•Presence of carbon in early rocks suggests life –Isotopic signature distinguishes from lifeless carbon sources1/12/13Earliest signs of life•Oldest evidence of life dates to 3.7 bya–Carbon contained in rocks–Claim is controversial•Oldest stromatolite (bacteria) fossils date to 3.45 bya Top: Living stromatolitesBottom: Fossil stromatolites1/12/13Key Concepts•Potential signs of life date to 3.7 bya but claim is controversial•Earliest accepted fossils of bacteria date to 3.45 bya•Microbes still constitute most of the earth’s biodiversity1/12/13How do early organisms fit in the tree of life?Earliest fossils: potentially 3.45 myo; abundant by ~2.6 mya, corresponding to rise in oxygen Earliest fossils: ~3.5 bya Earliest fossils: ~1.8 bya1/12/13Origin of multicellularity a major transition in history of life•Evolved independently in different lineages•Extant organisms provide clues about origin of multicellularity1/12/13Oldest fossils of multicellular life date back 2.1 million years•Unclear where they fit in the tree of
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