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Case study, the K orT extinction.docx

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GEOL 2207

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Case study, the K/T extinction (or K/P) 65 Ma K/T Extinction • Describe the character of extinctions at the K/T boundary  The dinosaur killer  At least 50% of all species lost  On land: nothing over 25kg survives  Not just terrestrial species, marine fauna suffers: ammonites/marine reptiles 80-90% lost • Discuss the evidence used to support the K/T impact  Water and Luis Alverez = latest cretaceous clay layer, enriched in iridium (iridium anomaly and clay layer is global)  Source of such high iridium? Comets/meteorites  Impact scenario  Fern spores vs. pollen: ferns first to colonize after fire impacted landscape (spores act as a proxy for forest fires) o After K/T, massive increase in “spike” in the % of spores in sediments that are from ferns  Soot layers associated with the iridium layer, evidence of massive global fires  Tektites: natural glass produced by melting rocks during impact  Shocked quartz: another impact feature, cross-hatched lines = stress lines in the quartz  Tsunami deposits: evidence of almost global tsunami activity at end of Cretaceous • Describe the location and probable nature of the K/T impactor  The Crater: the smoking gun, drilling off coast of Mexico (Yucatan Peninsula), odd rocks, completely melted rocks
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