Cretaceous-Tertiary (K-T) mass extinction

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  • Cretaceous-Tertiary (K-T) mass extinction
    • What do we know?
      • Around 65 million years ago
      • 75% of species became extinct
        • Marine = large reptiles, brachiopods, ammonites, coccoliths, foraminfera, belemnites, fish and some bivalves
        • Land = Dinosaurs, pterosaurs and plants
        • Animals like crocodiles, turtles, lizards, mammals and birds survived without many casualties
      • It was gradual showing decline in species over several million years before
        • Similar to Permo-Triassic
    • Impact of an asteroid or meteorite
      • Layer of iridium (transition element rare on Earth)
        • Found concentrated in clays at boundary
      • Shocked grains of quartz
        • Usually found around impact craters
        • Tektites have a very low water content suggesting not Earth formed or formed as the rock melted quick on impact
      • Large-scale sedimentary evidence in Texas of a large tsunami
      • Large meteorite crater found on the Yucatan Peninsula in Mexico at Chicxulub
        • Shown by gravity variations in the region
        • Circular depression around 180km in diameter
    • Major volcanic activity (Deccan Traps)
      • Enormous series of eruptions in India
        • Covered area of roughly 500,000km2
      • The volcanism was probably the same as with Siberian Traps


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