Lecture 1: What Happened to the Dinosaurs?
August 27, 2015
- 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
- Lastly, we will ask, "Did the dinosaurs really become
extinct?"
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