Earth's outer core

The outer core of Earth is liquid, unlike its inner core, which is solid. Evidence for a fluid outer core includes seismology which shows that seismic shear-waves are not transmitted through the outer core. Although having a composition similar to Earth's solid inner core, the outer core remains liquid as there is not enough pressure to keep it in a solid state. Seismic inversions of body waves and normal modes constrain the radius of the outer core to be 3483 km with an uncertainty of 5 km, while that of the inner core is 1220±10 km. Estimates for the temperature of the outer core are about in its outer region and near the inner core. Modeling has shown that the outer core, because of its high temperature, is a low-viscosity fluid that convects turbulently. As Earth's core cools, the liquid at the inner core boundary freezes, causing the solid inner core to grow at the expense of the outer core, at an estimated rate of 1 mm per year. This is approximately 80,000 tonnes of iron per second. == Light elements ==

Composition Earth's outer core cannot be entirely constituted of iron or iron-nickel alloy because their densities are higher than geophysical measurements of the density of Earth's outer core. The outer core is approximately 5 to 10 percent lower density than iron at Earth's core temperatures and pressures. Hence it has been proposed that light elements with low atomic numbers compose part of Earth's outer core, as the only feasible way to lower its density. the composition of light elements can be meaningfully constrained by high-pressure experiments, calculations based on seismic measurements, models of Earth's accretion, and carbonaceous chondrite meteorite comparisons with bulk silicate Earth (BSE). , estimates are that Earth's outer core is composed of iron along with 0 to 0.26 percent hydrogen, 0.2 percent carbon, 0.8 to 5.3 percent oxygen, 0 to 4.0 percent silicon, 1.7 percent sulfur, and 5 percent nickel by weight, and the temperature of the core-mantle boundary and the inner core boundary ranges from 4,137 to 4,300 K and from 5,400 to 6,300 K respectively. Implications for Earth's accretion and core formation history Tighter constraints on the concentrations of light elements in Earth's outer core would provide a better understanding of Earth's accretion and core formation history. Consequences for Earth's accretion Models of Earth's accretion could be better tested if we had better constraints on light element concentrations in Earth's outer core. These reactions are dependent on oxygen, silicon, and sulfur, In another example, the possible presence of hydrogen in Earth's outer core suggests that the accretion of Earth's water was not limited to the final stages of Earth's accretion Implications for Earth's magnetic field , silicon dioxide, and iron(II) oxide. Earth's magnetic field is driven by thermal convection and also by chemical convection, the exclusion of light elements from the inner core, which float upward within the fluid outer core while denser elements sink. This chemical convection releases gravitational energy that is then available to power the geodynamo that produces Earth's magnetic field. but one estimate is that the core would not be expected to freeze up for approximately 91 billion years, which is well after the Sun is expected to expand, sterilize the surface of the planet, and then burn out. ==See also==