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

The Cambrian Explosion

Lecture 17

 In the last two lectures, we looked at the fossil record from the late Precambrian and Cambrian times.
 Today we will use that record to look at the Cambrian Explosion.
Key Points
 The Cambrian Explosion is a unprecedented time in the evolution of metazoans
 Our understanding of the Cambrian Explosion is evolving
The fossil record
 Late Precambrian Fossils
 Ediacaran Fauna
 565 - 543 Ma
 Trace fossils
 Early Cambrian Fossils
 Tommotian stage
 543 - 530 ma
 Small shelly fossils (ssf)
 Atdabanian stage
 530 -520 ma
 Burgess Shale
 Chengjiang fauna, China
Time Constraints
 40 Million years
 565 to 525 Ma
 Development of nearly all of the modern metazoan phyla
Environmental Changes
 slowly increasing O2 levels
 end of Precambrian glaciation at 600 my
 global sea level rise
 increasing temperatures
Causes for the Cambrian Explosion
 Increasing O2 levels
 Crossed a threshold value that allows hard part production
 Simple genes
 Easier to have evolutionary experiments
 Led to an "arms race"
 Development of infauna
 vertically burrowing organisms
 development of teeth/predatory lifestyle