Lecture #1: Dinosaur Extinction
Tertiary-Cretaceous Boundary - Dinosaurs all disappeared 65 million years ago
Evidence for an impact - Layer of ash deposited worldwide.
The ash contains:
-- Rare earth element iridium more abundant than in earth.
-- Spherules of glass caused by melting during impact.
-- Quartz grains with shocked lamellae.
Effects of a large impact:
Immediate - Blast wave, base surge (dust cloud), tsunamis, vaporization of water and rock, earthquakes.
Short Term but Global (days to weeks) - global distribution of ejecta, global wildfires.
Long Term Global Effects (months to years) - Acid rain, Global darkness, Greenhouse effect.
Impact Craters:
Meteor Crater, Arizona — 1200 m wide, 180 m deep. Excavated 50,000 years ago by an iron meteorite about 30 m across.
Chicxulub Crater, Yucatan Mexico - half the size of the state of Connecticut. Hit the Earth about 65 million years ago. This is the crater responsible for the Cretaceous-Tertiary extinction event.
Manicouagan Crater, Quebec - 210 million years ago. Less than the size of Chicxulub but large enough to cause some extinctions.
Periodic extinction (every 26 million years) - Nemesis Theory which is that a companion star orbits our Sun over a period of 26 million years. The companion star is in a highly elliptical orbit passing through the Oort Cloud of comets outside of Pluto's orbit. On passing through the Oort cloud the gravitational field of the companion star throws many of the comets toward the earth.