Properties
The temperature of the outer core ranges from 4400 °C in the outer regions to 6100 °C near the inner core. Because of its high temperature, modeling work has shown that the outer core is a low viscosity fluid (about ten times the viscosity of liquid metals at the surface) that convects turbulently. Eddy currents in the nickel iron fluid of the outer core are believed to influence the Earth's magnetic field. The average magnetic field strength in the Earth's outer core was measured to be 25 Gauss, 50 times stronger than the magnetic field at the surface. The outer core is not under enough pressure to be solid, so it is liquid even though it has a composition similar to that of the inner core. Sulfur and oxygen could also be present in the outer core.
This growth rate is estimated to be 1 mm per year. As heat is transferred outward toward the mantle, the net trend is for the inner boundary of the liquid region to freeze, causing the solid core to grow.
Read more about this topic: Outer Core
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