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It originates in the fluid motions of the outer core. These geomagnetic reversals , analyzed within a Geomagnetic Polarity Time Scale , contain polarity intervals in the last 83 million years, with change in frequency over time, with the most recent brief complete reversal of the Laschamp event occurring 41, years ago during the last glacial period. Geologists observed geomagnetic reversal recorded in volcanic rocks, through magnetostratigraphy correlation see natural remanent magnetization and their signature can be seen as parallel linear magnetic anomaly stripes on the seafloor.
These stripes provide quantitative information on seafloor spreading , a part of plate tectonics. They are the basis of magnetostratigraphy , which correlates magnetic reversals with other stratigraphies to construct geologic time scales. Unstable isotopes decay at predictable rates, and the decay rates of different isotopes cover several orders of magnitude, so radioactive decay can be used to accurately date both recent events and events in past geologic eras.
Even the mantle, though it has an enormous viscosity , flows like a fluid over long time intervals. This flow is reflected in phenomena such as isostasy , post-glacial rebound and mantle plumes. In the atmosphere it gives rise to large-scale patterns like Rossby waves and determines the basic circulation patterns of storms.
In the ocean they drive large-scale circulation patterns as well as Kelvin waves and Ekman spirals at the ocean surface. Mineral physicists study the elastic properties of minerals; their high-pressure phase diagrams , melting points and equations of state at high pressure; and the rheological properties of rocks, or their ability to flow. Deformation of rocks by creep make flow possible, although over short times the rocks are brittle.
The viscosity of rocks is affected by temperature and pressure, and in turn determines the rates at which tectonic plates move. Its thermodynamic properties determine evaporation and the thermal gradient in the atmosphere.
The many types of precipitation involve a complex mixture of processes such as coalescence , supercooling and supersaturation. Physical properties of water such as salinity have a large effect on its motion in the oceans. This bulge is due to its rotation and is nearly consistent with an Earth in hydrostatic equilibrium. The detailed shape of the Earth, however, is also affected by the distribution of continents and ocean basins , and to some extent by the dynamics of the plates.
This is also implied by its low moment of inertia 0. However, some of the density increase is compression under the enormous pressures inside the Earth. The effect of pressure can be calculated using the Adams—Williamson equation. The conclusion is that pressure alone cannot account for the increase in density. This indicates that the outer core is liquid, because liquids cannot support shear. For a complete model of the Earth, mineral physics is needed to interpret seismic velocities in terms of composition.
The mineral properties are temperature-dependent, so the geotherm must also be determined. This requires physical theory for thermal conduction and convection and the heat contribution of radioactive elements. Some parts of this model have been updated by recent findings in mineral physics see post-perovskite and supplemented by seismic tomography. The mantle is mainly composed of silicates , and the boundaries between layers of the mantle are consistent with phase transitions.
This makes plate tectonics possible. The solar wind flows from left to right. The solar wind, a stream of charged particles, streams out and around the terrestrial magnetic field, and continues behind the magnetic tail , hundreds of Earth radii downstream. Inside the magnetosphere, there are relatively dense regions of solar wind particles called the Van Allen radiation belts.
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