Lecture 1: What Happened to the Dinosaurs?

January 21, 2020

• The Great Dinosaur Extinction occurred 65 million years ago, at the boundary between the Cretaceous and Tertiary Geological Time Periods

• Most modern explanations point to environmental and climatic changes, but they differ on the exact mechanism that triggered the changes.

• The two main hypotheses in the dinosaur extinction are:
      1) massive volcanic activity
      2) asteroid impact

• Can we test these ideas?
      -- yes, to some degree
      -- but can we distinguish between the effects of volcanic activity and an impact?

• First - What Happened?
      --  On land, the big dinosaurs disappears, along with some small ones
      --  Many other land organisms went extinct, including pterosaurs, some mammals
      --  50 to 80% of land plants disappeared
      --  In the oceans, many marine microscopic single-celled organisms (plankton) disappeared
      --  Many larger marine animals disappeared (rudistid clams, ammonites, many vertebrates, including plesiosaurs, ichthyosaurs, mosasaurs)

• The Volcanic Hypothesis
      -- mass extinction occurred gradually, acting over thousands to millions of years
      -- atmosphere is gradually polluted by high level of dust, ash, and toxic gasses
      -- lava flows pile up over large regions of the globe
      -- acid rain degrades terrestrial environment
      -- deteriorating environmental conditions cause decline in population levels of many species
      -- winter temperatures gradually cool; summers become hotter
      -- one by one, species die off until perhaps as many as half the world's species are gone

• The Asteroid Hypothesis
      -- mass extinction occurred instantaneously - in a few days or a few years - one generation
      -- an asteroid of enormous proportions strikes the Earth at between 50,000 to 150,000 miles per hour
      -- the impact blast is more than 1 million times greater than the strongest earthquake ever recorded
      -- about 5000 cubic miles of debris is ejected from the crater, throwing a great dust cloud into the atmosphere
      -- huge tidal waves scour across the continental margins
      -- wildfires incinerate the more inland regions
      -- atmosphere becomes so choked with debris and smoke that no sunlight penetrates to the ground
      -- plants died, herbivores starved, and so did the carnivores   

• Is either or some combination of both of these hypotheses true?    
  
•   There are three important criteria in testing the hypotheses:
      1) is there any geological evidence for the proposed mechanism?
      2) how did the effects of that particular mechanism affect the organisms that died, and why did the survivors survive?
      3) how well does the time-line for the proposed mechanism match the evidence in the rock and fossil record?
     
• In order to understand how test them, we will look at the "crime scene" to see what kinds of evidence are  preserved, and where in the world we have to go to see the evidence

• Time of the "crime"
      - approximately 65 million years ago
      - the extinction marked the end of the Cretaceous and beginning of the Tertiary time periods
      - the most direct evidence of the extinction is preserved in rocks of Cretaceous and Tertiary age

• Place:
      - the extinction is thought to have affected organisms all over the Earth
      - there are more than 100 locations around the world that record evidence of what happened in the oceans
      - there are only about 26 places that record what happened on land at the end of the Cretaceous

• Lastly, we will ask, "Did the dinosaurs really become extinct?"

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