Lecture XII: The Origin ofComplex Animal LifeLast LectureOutlineLectureEES 1040 1st Edition Lecture 11Lecture XII: The Origin ofComplex Animal LifeLast LectureExam IOutlineI. Schrag and HoffmanII. PrecambrianIII. First life looks lifeIV. Precambrian-Cambrian V. When did complex animal life start?LectureI. Schrag and HoffmanA. “Cap Carbonates”1. “Ice house” to GreenhouseB. C isotopes1. If no life and CaCO2 from seawater would have original ratio of 12C/13C2. If abundant life, burying organic C (preferentially 12C)a. LESS 12C available for CaCO3, so 13C is elevated3. ONSET OF GLACIATIONa. Major depletion of 13C all way down to near original source levelsII. PrecambrianA. 542MAstart of common fossil record1. first evidence of complex animal life2. GlaciationsB. 1.0BAi. Dominated by prokaryotes start to diversify (eurkaryotes)C. 1.6BA1. Paleoproterozoic2. 1.8a. Start of buildup of atmospheric oxygen3. 2.3D. 2.5BA1. Archaean Eon2. 3.2 first Stramatolites3. 3.5 first fossils4. 3.8 First evidence of lifeE. 3.96BA1. Hadean Eon no preserved recordF. 4.6BAIII. First life looks lifeA. ~580Ma1. Complex animals suddenly appear (only last 20-30 million years of “Precambrian”)2. “Ediacara Fauna” Ediacara hills of South Australia3. Soft-bodied animals preserved as imprints in sediment4. Weirda. Debate overi. Belong to extent Phyla- Vs.ii. Basically a separate Kingdom- “Vendobionta”- DolfSeilacherIV. Precambrian-Cambrian A. OrdovicianB. Cambrian1. Large Cambrian Cambrian Explosioni. Radiation2. Middle Cambrian Cambrian Explosioni. Radiation of complex large animals- “all” known phyla developedb. Sudden appearance of armored fossils3. Lower Cambriana. Sudden appearance of armored fossilsb. Trilobite tracks (but no trilobites (so no hard parts developed yet on the trilobites))c. Small, simple skeletal fossil “SSF” (small shelly fossils)C. 542MA latest Precambrian1. First hardparts2. First animal tracksD. ~570MA1. Ediacaran FaunaV. When did complex animal life start?A. “the molecular clock”1. We can measure the genetic difference or “distance” between different animals2. By estimating the rate of genetic change over time, we can calculate how long ago two different animals split from a common
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