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widened. These magnet- ic anomalies have now been age-dated, and sea- floor mapping based on the magnetic anomalies is shown in figure 1. The distribution of the oceanic geology demon- strates that all the oceans contain mid-ocean ridges, and distribution of geology symmetrical about, and parallel to, the mid-ocean-ridge axes demonstrates that the sea-floor crust ages away from the mid-ocean ridges, with the oldest Early Jurassic crust located adjacent to the continents. More impor- tantly, the oceanic geolo- gy demonstrates that all the oceans are enlarging approximately normal to the ridge axes, and all continents are now mov- Figure 1. Bedrock geological map of the world showing continental and oceanic time-based geology. Oceanic mapping in each of the oceans represents the main geological periods, ranging from the Recent along the mid-ocean ridges to the Early; Jurassic adjacent to the continents. The map is shown to 80 degrees north and south latitudes only. (After the Geological ing away from each other Map of the World, published by CGMW & UNESCO, 1990) as the sea floor enlarges. The current rate of sea-floor spreading in each of the oceans GLOBAL EXPANSION TECTONICS varies between | to 10 centimetres per year. Empirical modelling and investigation into Earth expansion To account for sea-floor spreading in all the oceans, though, we from the Archaean era to the present is based on the published must consider the presumption that either: Bedrock Geology of the World map (CGMW & UNESCO, 1990) (a) the Earth's radius has remained constant throughout geologi- (figure 1). The geology shown in this map is time-based, which cal time, and, to compensate for lava added along the spreading means that the continental bedrock geology represents the major _ ridges, older pre-existing crust is continuously disposed of along geological aeons (Archaean, Proterozoic) and eras (Palaeozoic, inferred subduction zones located around the Pacific margin, dis- Mesozoic, Cenozoic), and oceanic geology represents the geologi- _ placing and recycling the crust into the mantle to maintain a con- cal periods (subdivisions of the Mesozoic and Cenozoic eras) stant total surface area, i.e., plate tectonics; or ranging from the Jurassic period to the Recent. (b) the Earth's radius has increased with time as lava is added at The oceanic geology shown in this map was compiled from spreading ridges. In this concept, sea-floor crust older than the magnetometer surveys, sea-floor drilling and radiometric and Early Jurassic period does not exist, subduction of crust is not palaeontologic age-dating over the oceans, carried out during the —_ required, and an increase in the Earth's surface area is a measure 1960s to 1980s. Geophysical surveys covering all the world's of the rate of change in the Earth's radius with time, i.e., Earth oceans revealed long, linear, magnetic anomalies in the sea floor —_ expansion. that are symmetrical about, and parallel to, mid-ocean ridges To quantify Earth expansion, spherical models of the ancient located centrally within each of the oceans. These anomalies Earth were constructed by progressively removing sea-floor crust were interpreted by geophysicists as evidence for sea-floor parallel to the mid-ocean ridges and refitting the crust along each spreading, where mantle-derived lava wells up along the length of — mid-ocean ridge at a reduced Earth radius. Each model shown in the ridge axes as the central spreading zones are continuously figure 2, for the Indian Ocean, and figure 3, for the Atlantic Empirical modelling and investigation into Earth expansion from the Archaean era to the present is based on the published Bedrock Geology of the World map (CGMW & UNESCO, 1990) (figure 1). The geology shown in this map is time-based, which means that the continental bedrock geology represents the major geological aeons (Archaean, Proterozoic) and eras (Palaeozoic, Mesozoic, Cenozoic), and oceanic geology represents the geologi- cal periods (subdivisions of the Mesozoic and Cenozoic eras) ranging from the Jurassic period to the Recent. The oceanic geology shown in this map was compiled from magnetometer surveys, sea-floor drilling and radiometric and palaeontologic age-dating over the oceans, carried out during the 1960s to 1980s. Geophysical surveys covering all the world's oceans revealed long, linear, magnetic anomalies in the sea floor that are symmetrical about, and parallel to, mid-ocean ridges located centrally within each of the oceans. These anomalies were interpreted by geophysicists as evidence for sea-floor spreading, where mantle-derived lava wells up along the length of the ridge axes as the central spreading zones are continuously ‘a) (c) (a) (e) if) (g) {h) (i) {i} Figure 2. Expanding Earth reconstructions of the Indian Ocean for the beginning of the (a) Recent, (b) Pliocene, (c) Miocene, (d) Oligocene, (e) Eocene, (f) Palaeocene, (g) Late Cretaceous, (h) Mid Cretaceous, (i) Early Cretaceous and (j) Late Jurassic periods. Each ancient Earth model was constructed by pro- gressive removal of sea-floor crust, shown in figure 1, and reuniting plates along each mid-ocean ridge at a reduced Earth radius. (2) if (a) (h) {i) ti 42 - NEXUS GLOBAL EXPANSION TECTONICS OCTOBER — NOVEMBER 2000