The terrestrial environment, crust and material cycling

Terrestrial environments consist of solid (rocks, sediments and soils), liquid (rivers, lakes and groundwater) and biological (plants and animals) components. The chemistry of terrestrial environments is dominated by reactions between the Earth s crust and fluids in the hydrosphere and atmosphere. 

silt and sandy sediments form mainly by weathering—the breakdown and alteration of solid rock. Usually, these sedimentary particles are transported by rivers to the oceans, where they sink onto the seabed. Here, physical and biological processes and chemical reactions (collectively known as diagenesis) convert sediment into sedimentary rock. Eventually these rocks become land again, usually during mountain building (orogenesis). 

The geological record shows that this material-transport mechanism has operated for at least 3.8 billion years. New sediments are derived either from older sedimentary rocks or from newly generated or ancient igneous and metamorphic rock. The average chemical composition of suspended sediment in rivers, sedimentary mudrock and the upper continental crust is quite similar (Table 4.1). 

Rivers 89 Present dissolved load 17%, suspended load 72%. Present suspended load higher than geological past due to human activities (e.g. deforestation) and presence of soft glacial sediment cover 

Glacier ice 7 Ground rock debris plus material up to boulder size. Mainly from Antarctica and Greenland. Distributed in seas by icebergs. Composition similar to average sediments 

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