Figure 4From: Ordovician ash geochemistry and the establishment of land plantsChemical Index of Alteration (CIA) for ashes and soils. Modern [60] and Ordovician volcanic ash (tuff) (sources in Additional file 1) show lower values than Precambrian soils [56]. Modern soils [56] show wide-ranging values, reflecting varying involvement of plants in different climates.Back to article page