Primeval 10 – Devonian Period

 

Between 419 and 359 million years ago, the Earth was in what is known as the Devonian Period, also known as the Age of Fish do to the abundance of fish species found in the geological record. During this Period the forests first spread across the inland regions of the continents, and the first terrestrial insects became well-established on land. The Devonian was a relatively warm period, and probably lacked any glaciers. The weather was also very arid, especially in equatorial regions.(1)M. M. Joachimski et al. (2009) “Devonian climate and reef evolution: Insights from oxygen isotopes in apatite” Earth and Planetary Science Letters Volume 284 Number 3–4, Pages 599–596 Reconstruction of tropical sea surface temperature from seashell remain implies an average value of 30 °C (86 °F) in the Early Devonian. Carbon-dioxide levels dropped steeply throughout the Devonian period as the burial of the new land based forests drew carbon out of the atmosphere into the sediment. This may be reflected by a Mid-Devonian cooling of around 5 °C (9 °F). The Late Devonian warmed to levels similar to the Early Devonian, however there is no corresponding increase in carbon-dioxide levels.

Earth 370 Million Years Ago

Earth 370 Million Years Ago

At the end of the Devonian Period came the Late Devonian extinction, which was one of five major known extinction events in the existence of the Earth. A major extinction, the Kellwasser Event occurred at the boundary that marks the beginning of the last phase of the Devonian period, about 374 million years ago.(2)George R. McGhee Jr. (1996) The Late Devonian Mass Extinction: the Frasnian/Famennian Crisis A second distinct mass extinction, the Hangenberg Event closed the Devonian period(3)Mark L. Caplan and R. Mark Bustin (1999) Devonian-Carboniferous Hangenberg mass extinction event, widespread organic-rich mudrock and anoxia: causes and consequences around 359 million years ago. Overall 19% of all families and 50% of all genera went extinct. By the late Devonian, the land had been colonized by plants and insects. In the oceans were massive reefs built by corals and stromatoporoids. Euramerica and Gondwana were beginning to converge into what would become Pangaea. The extinction seems to have only affected marine life. Hard-hit groups include brachiopods, trilobites, and reef-building organisms. Coral reefs only returning upon the evolution of modern corals during the Mesozoic. The causes of these extinctions are unclear.

The Age of Fish

The Age of Fish

The Kellwasser Event involved widespread oceanic anoxia, although the atmosphere doesn’t seem to have changed immediately. If this anoxia was caused by the same cause as modern anoxic dead-zones in the ocean, then they could have been caused by wide-scale agricultural runoff. Currently nitrogen-rich fertilizers are finding their way to the oceans via our rivers, and poisoning the continental shelves, creating localized areas similar to the global oceanic anoxia found in shale deposits from the late Devonian.(4)David K. Brezinski et al. (2009) Evidence for long-term climate change in Upper Devonian strata of the central Appalachians The secondary Hangenberg Event appears to have affected not only the ocean, which became anoxic, but also the atmosphere, as terrestrial life also died off.(5)Lauren Cole Sallan and Michael I. Coates (2010) End-Devonian extinction and a bottleneck in the early evolution of modern jawed vertebrates. Could a quasi-intelligent species like modern humanity have caused it’s own extinction event? There doesn’t seem to be any evidence of a quasi-intelligence evolving at the time, therefore it is more likely that the event was caused by a temporary extraterrestrial agricultural colony, or some unknown natural disaster.

References   [ + ]

1. M. M. Joachimski et al. (2009) “Devonian climate and reef evolution: Insights from oxygen isotopes in apatite” Earth and Planetary Science Letters Volume 284 Number 3–4, Pages 599–596
2. George R. McGhee Jr. (1996) The Late Devonian Mass Extinction: the Frasnian/Famennian Crisis
3. Mark L. Caplan and R. Mark Bustin (1999) Devonian-Carboniferous Hangenberg mass extinction event, widespread organic-rich mudrock and anoxia: causes and consequences
4. David K. Brezinski et al. (2009) Evidence for long-term climate change in Upper Devonian strata of the central Appalachians
5. Lauren Cole Sallan and Michael I. Coates (2010) End-Devonian extinction and a bottleneck in the early evolution of modern jawed vertebrates.