Earth's outer core is a liquid layer about 2,266 km (1,408 mi) thick composed of iron and nickel that lies above Earth's solid inner core and below its mantle. Its outer boundary lies 2,890 km (1,800 mi) beneath Earth's surface. The transition between the inner core and outer core is located approximately 5,150 km (3,200 mi) beneath the Earth's surface.
The temperature of the outer core ranges from 4,300 K (4,030 °C; 7,280 °F) in the outer regions to 6,000 K (5,730 °C; 10,340 °F) 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 2.5 millitesla, 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.
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 inner core to grow. This growth rate is estimated to be 1 mm per year.
Effect on life
Without the outer core, life on Earth would be very different. Convection of liquid metals in the outer core creates the Earth's magnetic field.
- Gillan, Michael J.; De Wijs, Gilles iA.; Kresse, Georg; Vočadlo, Lidunka; Dobson, David; Alfè, Dario; Price, Geoffrey D. (1998). "The viscosity of liquid iron at the physical conditions of the Earth's core". Nature 392 (6678): 805. Bibcode:1998Natur.392..805D. doi:10.1038/33905.
- First Measurement Of Magnetic Field Inside Earth's Core. Science20.com. Retrieved on 2012-01-27.
- Buffett, Bruce A. (2010). "Tidal dissipation and the strength of the Earth's internal magnetic field". Nature 468 (7326): 952–4. Bibcode:2010Natur.468..952B. doi:10.1038/nature09643. PMID 21164483.
- Gubbins, David; Sreenivasan, Binod; Mound, Jon; Rost, Sebastian (May 19, 2011). "Melting of the Earth's inner core". Nature 473 (7347): 361–363. Bibcode:2011Natur.473..361G. doi:10.1038/nature10068. PMID 21593868.
- Waszek, Lauren; Irving, Jessica; Deuss, Arwen (2011). "Reconciling the hemispherical structure of Earth's inner core with its super-rotation". Nature Geoscience 4 (4): 264–267. Bibcode:2011NatGe...4..264W. doi:10.1038/ngeo1083.