K/Pg (Cretaceous/Paleogene) Extinction

• the dinosaur killer

• at least 50% of all species were lost

  • classified as an intermediate mass extinction

• nothing over 55 pounds on land survives

• this didn’t just happen to land species

• marine animals suffered too

  • example: ammonites, marine reptiles

  • 80-90% of marine species were lost

Iridium Anomaly

• chemical element that’s much more abundant in meteoroids than on Earth

• last clay layer formed during the Cretaceous is strongly enriched in iridium

• it was noticed first in Gubbio, Italy, but it was a global phenomenon

The Smoking Gun: Chicxulub Crater

• years before a crater was discovered, “odd”, melted rocks were found

• melted rocks weren’t explored further until…

• gravity survey revealed a 93 mile diameter crater

  • shallow entry (20-30 degrees)

  • 6.8-50.3 mile diameter impactor

Meteorite Effects

• initial effects:

  • vaporizes everything close by

  • causes wildfires

  • generates tsunamis

• longer term effects:

  • sunlight shut off

    • photosynthesis effectively stops on land and in oceans for up to several months

• even longer-term effects:

  • up to 18 degree Fahrenheit global warming

    • water vapor remains in the atmosphere after the dust clears

    • CO2 produced from vaporization of certain rocks during the impact

  • acid rain

    • NOx (oxides of nitrogen) formed due to impact combined with the water in the atmosphere →nitric acid

      • oceans and soils acidified