Late Devonian
Origin of woody trees
The Late Devonian (383–359 Ma) occurs after the Givetian of the Middle Devonian, and before the Tournaisian of the Mississippian
Geologic Age
382.7–358.9 Ma
Subdivisions
Eon / Era / Period / Epoch
What happened during this time?
Biological
The appearance of trees with a vascular cambium and lateral growth.
Plants with robust, woody growth are called Lignophytes.
The progymnosperm, Archaeopteris, is the oldest known woody tree.
Plants clearly identified as sphenopsids, Xihuphyllum, appear (Huang et al. 2016)
Early rhizomorphic lycopsids appear on the landscape
Cymastrobus, an isoetalean from the Late Devonian of Australia (Evreïnoff et al. 2017)
Increase in the number of seed plants
Several early seed plants are found in Famennian sediments from around the world: Elkinsia, Moresnetia, Archaeosperma, Hydrasperma, etc.
Above: Diagram of representative plant groups during the Late Devonian
Left: Late Devonian reconstruction showing fish and amphibians in water, and Archaeopteris forest in the background
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
Above: Reconstruction of Xihuphyllum, an early sphenopsid from the Late Devonian
Additional Reading
Algeo, T.J. 1998. Terrestrial-marine teleconnections in the Devonian: links between the evolution of land plants, weathering processes, and marine anoxic events. Phil. Trans. R. Soc. Lond. B 353: 113-130.
The Root of an Ancient Mass Extinction (In Defense of Plants 18Dec2022)
A new theory emerges for where some fish became four-limbed creatures (Phys.org 27Dec2011)