The End of an Era - The Mesozoic/Cenozoic Mass Extinction

• EXTINCTION OF:
• Ichthyosaurs, plesiosaurs, & mosasaurs;
• Ammonoids, belemnites, rudist bivalves,
• Families of echinoids,bryozoans,
• Families of planktonic forams & calcareous phytoplankton.
• Dinosaurs & pterosaurs.
• Many forms of life that had played major ecologic roles for tens of millions of years disappeared.

• Possible Causes for Faunal Extinctions
• Early 1980s University of California at Berkeley discovered a layer of sediment at the K/T boundary containing 30% more Iridium than in rocks above or below.
• Iridium is so rare on Earth that enriched layer came from space.

• Bolide impact theory of Alvarez.
• Iridium in low concentrations in earth's crust and possible volcanism to account for anomaly.
• Asteroid impacted Earth producing large cloud of iridium dust and other impact ejecta.
• Dust cloud blocked sunlight, causing the loss of photosynthetic organisms, and resulting in global thermal lowering.

• Mt. Tambora Eruption 1816
• 4200' Elevation Loss
• 25 mi3 ejecta into atmosphere
• High altitude circulation to North America

• Acid Rain. The energy released by impact caused atmospheric oxygen and nitrogen to form oxides; contact with water vapor results in nitric acid. This would rain out as acid rain.
• Wildfires. Particles of charcoal & soot found at the boundary horizon with iridium. Interpreted to be remains of great fires that spread across the globe when the hot meteorite hit the Earth.

• Iridium anomaly
• Widespread occurrence of shocked quartz
• Tektites & Glass Microspheres
• Widespread charcoal layer
• Impact Site

• Change in flora to 99% fern spores.
• 75% taxa disappear in subtropical floras (N.Mex.)
• Mid-latitude temperate response (50%)
• Northern (25%) floras less affected
• Plants survived include high number of toothed margined leaves (adapted to deciduous habit).

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