Late Devonian Epoch

Geophysical

• "Biotic crisis" decimates tropical marine environments (Algeo et al. 1995, Algeo and Scheckler 1998)

  • Land plants, in particular evolving forests, may have increased weathering of rocks and soils, producing an influx of minerals to the marine env't (Smart et al. 2022)

  • Both an increase in root depth and penetration as well as the ability of seed plants to colonize drier, upland env'ts may have contributed to increased soil formation (pedogenesis)

    • Plant roots fracture rocks exposing more surface area to carbon dioxide and water 

    • They also introduce organic acids that directly weather rocks chemically

  • Enhanced soil formation by plants “resulted in elevated fluxes of soil solutes (especially biolimiting nutrients) as a consequence of (1) enhanced mineral leaching, (2) fixation of nitrogen by symbiotic root microbes, and (3) shedding of plant-derived detrital carbon compounds … [and] elevated river-borne nutrient fluxes may have promoted eutrophication of semi-restricted epicontinental seas and stimulated algal blooms” (Algeo et al., 2001, 233). 

  • Increased nutrient input on rivers creates eutrophic conditions in epicontinental seaways, "resulting in algal blooms, widespread bottom water anoxia, and high sedimentary organic carbon fluxes" (Algeo and Scheckler 1998).

    • There is an accumulation of unoxidized organic hydrocarbons in black shales, rather than returning the carbon to the atmosphere through normal aerobic respiration by bacteria (Carmichael et al. 2016)

• Volcanic eruptions have also been cited as a possible cause of the Late Devonian mass extinction (Racki et al. 2018)

• An increase in plant biomass causes a draw-down of atmospheric CO2, and results in global cooling and glaciation. (Algeo et al., 1995)

  • Archaeopteris covered vast coastal and lowland areas of the Earth by the late Frasnian removed carbon from the atmosphere to form organic hydrocarbons

  • The increased burial rate of organic carbon on land began the process of depleting carbon dioxide in the atmosphere