Geology 105: History of Life
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Lecture Notes
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Introduction and Overview
Fossils 1
Fossils 2
Geologic Principles
Relative Time
Absolute Time
Diversity of Life
Evolution and Diversity
Rates of Evolution
Plate Tectonics
Origin of the Earth
Origin of Life
Early Precambrian (Archean) Life
Late Precambrian (Proterozoic) Life
The Cambrian Explosion
Early Paleozoic Life
Late Paleozoic Marine Life
The Invasion of Land 1
The Invasion of Land 2
The Permo-Triassic Extinctions
Mesozoic Marine Life
Mesozoic Terrestrial Life
Cretaceous-Tertiary Extinctions
Cenozoic Life

Cretaceous-Tertiary Extinctions

Lecture 25

 The Cretaceous-Tertiary extinctions resulted in the extinction of the dinosaurs and many other groups. As a result it opened environments and paved the way for modern floras and faunas.
Key Points
 The Cretaceous-Tertiary extinctions are one of the major extinction events in the history of life
 Unlike the Permian-Triassic extinctions, the Cretaceous-Tertiary extinctions appear to be sudden.
 An asteroid impact at the time appears to have played a major role in the extinction.
Magnitude of Extinction
 Marine Biosphere
 15% of all marine families
 50 % at generic level, maybe 80-90 % of all species
 concentrated on planton, marine predators, and shallow water communities
 Terrestrial Biosphere
 25 % of terrestrial families
 56 % at generic level
 nothing bigger than 25 kg survived
 Generally unaffected
 higher plants 10 %
 dinoflagellates 5 %
 mammals + 20 %
 Appears to be very sudden
 The Cretaceous-Tertiary boundary sediments
 well described around the world
 can be shown to be a single bed
 At Gubbio, Italy
 A wide range of suggested
 climatic change to dinosaur blindness
 several events took place at or near the boundary
 Volcanic Eruptions
 Deccan Traps basalt
 Asteroid Impact
 Discovery of irridium in boundary clay
 Similary deposits were found world wide
 Stevns Klint in Denmark
 New Zealand
 In North America
 Other materials in the boundary layer
 shocked quartz
 Origins of the irridium
 Irridium is rare on the surface of the earth
 Irridium is much more common in space
 Discovery of an Impact Crater
 Chicxulub Impact structure
 Buried beneath the Yucatan Peninsula
 150 - 300 km in diameter
 Age dates of melt rock in the structure have at date of 65 Ma
Did the Impact cause the extinctions?
 This remains an issue of contention
 You must explain all of the extinctions
 We don't understand all of the implications the event
 General Scenerio
 Impact wipes out most plankton & primary production
 This lose travels up the food chain and heavily impacts top order consumers
 Smaller organisms may survive by burrowing, hibernating, or migrating
 Shallow marine faunas hit by acid rains and temperature changes
 Plants & planton return from resting spores & seeds to repopulate planet.