Speculated Causes For the Cambrian Extinction
The two most accepted current hypotheses for the Cambrian extinction are:
- Glaciation in the early
Ordovician
- Cooling and depletion of oxygen
in marine waters
Glacial Cooling Hypothesis
The advancement of the theory of glaciation as the predetermining agent for the Cambrian extinctions has been developed by James F.Miller of Southwest Missouri State University. Through research undertaken by Miller, evidence of early Ordovician sediment of glacial origin has been uncovered in South America.
Miller suggests in his hypothesis that this evidence of
continental glaciation at the Cambrian-Ordovician boundary is responsible for a decrease in global climatic conditions. Such a decline in temperature is implied by Miller to destroy Cambrian fauna which are intolerant of cooler conditions, producing a mass extinction of mostly warm water species. He also suggests that a significant continental glaciation would bring large amounts of ocean water onto the land in the form of frozen glacial ice. This trapping of ocean water inevitably results in the decrease of sea-level and the withdrawal of shallow seas. Miller implicates that this reduction in sea-level would produce reduced habitat for marine species as continental shelves are obliterated. Ecological competition would consequently ensue, perhaps acting as a driving agent for extinction.
Oxygen Depletion Hypothesis
The development of a hypothesis invoking the cooling and depletion of water in marine waters as a causative agent for the Cambrian extinctions has been advanced by several geologists, primarily Allison Palmer and Michael Taylor of the U.S. Geological Survey and James Stilt of the University of Missouri. The cooling and oxygen depletion would occur when cool waters from deep zones of the ocean spread up onto the continent, eliminating all organisms not able to tolerate cool conditions. The cooling would also result in stratification of the water column. Thus, species would ultimately perish due to their inability to tolerate dramatic shifts in such limiting factors as temperature and oxygen availibility.
Further research is required to more fully test the validity of the above outlined Cabrian extinction hypotheses.
Ordovician Mass Extinction
Mass Extinctions of the Phanerozoic Menu
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