Terrestrialization: The origin and early evolution of the terrestrial landscape

The palæontological evidence for evolution in non-marine habitats, prior to the origin of land plants, is actually quite sparce. Our research on cryptospores yields a limited view on the biology of charophyte algae that were adapting to subærial conditions during the middle Cambrian to mid-Silurian interval. According to the antithetic theory of Bower (1908), it was during this time that the plant sporophyte evolved complex multicellularity during its interpolation into a charophytic life cycle. Precambrian palæontology of non-marine settings is limited to a very few deposits, such as the ca. 1Ga Nonesuch Shale and the Diabaig Shale, and most evidence of biological activity on the Earth's surface during Precambrian time is baed on interpretations of geochemical signals from marine rocks. The existence of early terrestrial microfloras has been recently reviewed by Wellman, C. H. and Strother, P. K. (2015), The terrestrial biota prior to the origin of land plants (embryophytes): a review of the evidence. Palaeontology, 58: 601–627. doi:10.1111/pala.12172.

Various organisms from the lacustrine Diabaig Shale, Torridonian Series. From Wellman & Strother (2015).

Sequoia sempervirens in Muir Woods National Monument, California.

The origin of a forested landscape represents the beginning of the Modern Carbon Cycle, as it coincides with all atmospheric composition models that show a drawdown of carbon dioxide beginning in the Cambrian. Although this did not occur until the middle to late Devonian, there is ongoing debate as to how much the Earth was affected by the terrestrial carbon cycle prior to the accumulation of standing carbon biomass as lignophytes evolved.

Precambrian islands composed of Shinumo Quartzite, in the eastern Grand Canyon, protrude through middle Cambrian sediments of the Tonto Group. In some cases the weathered debris of this Cambrian landscape are found embedded in the former sands of the Tapeats embayment. Today these weathered Shinumo quartzites are strewn on top of the similar boulders buried 500 Myr ago.

Cambrian Islands.pptx

Lacustrine algae Moyeria uticaensis Thusu 1973 and Tapetisphaerites sp. Miller & Wood 2001co-occur in the Tuscarora Fm (Aeronian) at Mill Hall, Pennsylvania. Here is a plate of additional specimens of Tapetisphaerites from the Tuscarora Formation.