Smithsonian National Museum of Natural History Geologic Time The Story of a Changing Earth
Presented by the Department of Paleobiology.
The Devonian
Contents
Overview
Life in the Devonian Seas
Terrestrial Habitats Conquered
The Devonian Extinction
and Tectonics during the Devonian
Evidence
Leaf and wood of Archaeopteris.
learn more
sample
Placoderm
Ammonite
Shark
Brachiopods
Trilobites
Centipede
Lobe-finned fish
Amphibian skull
references and links
Foundational Concepts
Dating Methods
Earth Processes
Life Processes
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The Devonian Extinction
Toward the end of the Devonian, nearly 70% of all invertebrate species vanished during the Late Devonian extinction. Marine species (especially tropical ones) suffered the most extinctions, followed by freshwater species, whereas terrestrial species were hardly affected. In particular, tabulate coral/stromatoporoid reefs vanished entirely, leading to a great decline in worldwide coral reef-building until the Triassic Period. Many species of brachiopods, trilobites, and early fishes went extinct, as did the planktonic graptolites. These extinctions were not the result of a single major extinction event, but rather smaller extinction events that occurred over a period of more than 20 million years.

The causes of the extinctions are uncertain, although there are several viable hypotheses. Most of these focus on the theory that the expansion of terrestrial plants decreased the amount of carbon dioxide in the atmosphere through two separate processes. One process is chemical weathering, a process that uses up carbon dioxide from the atmosphere, and that plants accelerate. The second process is carbon storage. Plants fix carbon dioxide from the atmosphere and convert it to organic carbon, stored in their stems, roots, and leaves. After plants die the organic carbon can be released to the soils. Both of these processes would have increased as terrestrial vegetation spread, reducing the amount of carbon dioxide in the atmosphere, triggering global cooling and eventually glaciation. An asteroid impact may also have occurred at this time.




Overview | Life in the Devonian Seas | Terrestrial Habitats Conquered
The Devonian Extinction | Climate and Tectonics during the Devonian



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