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The End of the Devonian Period:
A Mass Extinction
Alexandra Allen
San Francisco Sate University
Earth Science Department
Life Flourishes Throughout the Period:
During the Devonian, a majority of the Earth was covered in a vast ocean,
giving marine life the ability to evolve and thrive. Some species hat evolved in
the Devonian were the first of their kind such as:
Ammanoid Cephlapods
Gnathostomes
Siliceous Sponges
Life Flourishes Throughout the Period:
And many other species evolved and expanded, including:
Spiny Acanthodians
Osteichthyans
Placoderms
Chondrichthyan Fish
Sacopterygians
Actinopterygians
Trilobites
Mass Extinction of Marine Life:
The Devonian Period ends with a series of mass extinctions that
wipe out nearly 70% of all invertebrate species. Tropical marine
species suffered the most loss, followed by freshwater species.
The Devonian extinction occurred over a period of 20 million
years, leading paleoscientists to speculate on the causes.
There are two theories as to the domino effect of Devonian Extinctions…
Both based on the idea that expanding erogenous plants decreased the
amount of Carbon Dioxide in the atmosphere, leading to a cooling planet, and
eventually, glaciation of the Southern Pole.
Devonian Extinction Theories:
Cooling of Earth due to CO2 Decreases
1) Chemical Weathering- This process creates Calcium and
Magnesium, removing CO2 from the atmosphere, and cooling
Earth.
2) Carbon Storage- Plants convert CO2 to Carbon which is then
stored inside the plant structure. When it dies, the Carbon is
released into soils. Through weathering, CO2 is again removed
from the atmosphere effectively cooling the Earth.
Why does the Earth Cooling and Glaciation matter?