430 EARTH SYSTEM SCIENCE EARTH SYSTEM SCIENCE R C Selley, Imperial College London, London, UK ß 2005, Elsevier Ltd All Rights Reserved Introduction What on Earth is Earth System Science? Earth system science is founded on the precept that the Earth is a dynamic system that is essentially closed materially, but open with respect to energy This statement needs to be qualified by noting that the Earth continues to accrete matter from space in the form of meteorites, asteroids, and comets Incoming energy is principally derived from solar radiation at a rate that may fluctuate with time Earth processes in the lithosphere, the biosphere, and the atmosphere are linked, with a change in one impacting on one or more of the others Earth system science has grown out of an appreciation of the need to integrate geology with other scientific disciplines, not only to understand the planet on which we live, but also most particularly to predict its future in general and climate change in particular Earth system science requires a holistic approach to education in which students learn geoscience, bioscience, climatic science, astroscience, and space science synchronously and seamlessly The Genesis of Earth System Science In the fourteenth century Richard de Bury (Bishop of Durham 1333–45) divided all research into ‘Geologia’ (geology), the study of earthly things, and ‘Theologia’ (theology), the study of heavenly things Masons, miners, and engineers were the first investigators of rocks The Church taught them that the Earth was an inert mass of rock formed in days Subsequently natural philosophers pondered the meaning of fossiliferous strata and how it was that they were intruded by crystalline rocks and truncated by unconformities Gradually it dawned on these natural philosophers that the rocks were not formed in an instant, but resulted from processes, many of which could be observed on the modern surface of the Earth This was formulated in Hutton’s principle of uniformitarianism, (see Famous Geologists: Hutton) and was epitomized in the dictum that ‘the present is the key to the past.’ As Lyell (see Famous Geologists: Lyell) wrote in his Principles of Geology in 1834: The entire mass of stratified deposits in the Earth’s crust is at once the monument and measure of the denudation which has taken place By the beginning of the twentieth century it was realized that the history of the Earth could be interpreted in terms of cycles Davies (1850–1934) recognized the landscape cycle, commencing with uplift, followed by youthful, mature, and senile landforms, followed by rejuvenation Stratigraphers recognized cycles of weathering (see Weathering), erosion, transportation, deposition, and diagenesis Sedimentologists discovered that all sedimentation is cyclic, although some is more cyclic than others The hydrologic cycle was revealed, in which water fell as rain on land, flowed into rivers, was discharged into the world’s oceans, evaporated and reprecipitated Geochemists identified the cycles of carbon (see Carbon Cycle) and other key elements, such as nitrogen, oxygen, and sulphur Agassiz (1807–73) (see Famous Geologists: Agassiz) was the first geologist to establish the existence of ancient glaciation Subsequently evidence accumulated for past climatic cycles of alternating ‘greenhouse’ and ‘icehouse’ phases, as they became picturesquely termed Thus cyclicity was revealed in rocks, water, and air – or the lithosphere, the hydrosphere, and the atmosphere The extent to which these cycles interrelated with one another was little understood Initially palaeontologists took the view that the evolution of the biosphere responded to external changes, and had little inter-reaction with them Subsequently it was realized that this is far from the case The stromatolitic limestones (see Fossil Plants: Calcareous Algae) of the Late Precambrian, some 3400 My BP, are a dramatic example (Figure 1) These limestones are the relicts of primitive algae and cyanobacteria They are found worldwide in Late Precambrian and Phanerozoic strata, and form today in tidal-flat environments Stromatolitic limestones provide the earliest case preserved in the stratigraphical record of the interaction of organic and inorganic processes to form rock Their creators, the first abundant photosynthesizers, took carbon dioxide from the atmosphere, replaced it to some degree with oxygen, extracted calcium from sea water, and precipitated the vast limestone rock formations that are preserved all over the world to this day (see Atmosphere Evolution) Analysis of ice cores from modern polar regions shows a strong positive correlation between carbon