%0 Journal Article
%T Ordovician ash geochemistry and the establishment of land plants
%A John Parnell
%A Sorcha Foster
%J Geochemical Transactions
%D 2012
%I BioMed Central
%R 10.1186/1467-4866-13-7
%X The establishment of land plants in the terrestrial environment brought about a fundamental transformation of the Earth¡¯s surface [1-7]. It involved new soils and soil microbiota, greatly enhanced biological weathering and new controls on landforms and erosion, a new food chain, and new habitats for animals that increased their diversity. It also enhanced the influence of photosynthesizers on the planet's atmosphere, increasing oxygen concentrations and drawing down carbon dioxide by biological weathering [1]. The Earth¡¯s surface biomass is now dominated by land plants [8], and is so extensive that the occurrence of life on Earth would be evident to observers from space [9]. The establishment of this high surface biomass represented a crucial shift from a planet dominated by subsurface life to one in which surface life became proportionately significant. This change intrinsically involved an increase in the proportion of life ultimately supported by photosynthesis (carbon dioxide) rather than hydrogen.Understanding the colonization of the land surface by plants requires us to identify if special geochemical circumstances had arisen to promote it, or if it was simply an aspect of a wider diversification of life into new niches. This event is dated to the early/mid-Ordovician. There are several records of Ordovician plant spores, extending back to an Arenig (Floian; 476 Ma) occurrence of liverwort-type spores [10-13], and fungal hyphae in the Ordovician could have been closely associated with evolving plants [14,15]. Plant growth is envisaged to have been sufficiently extensive and well-anchored to trigger the end-Ordovician glaciation by weathering-drawdown of CO2[7]. An essential requirement to allow colonization of the subaerial environment was the availability of nutrients in the soil rather than through water. The ready availability of nutrients requires some kind of soil, in which mineral matter can dissolve into pore waters at a fast rate. For much of Earth¡¯s h
%K Ash geochemistry
%K Tuff
%K Land plants
%K Chemical index of alteration
%K Phosphorus
%K Biomass
%K Ordovician
%U http://www.geochemicaltransactions.com/content/13/1/7