Earth's core

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Structure of Earth

The Earth's core is the part of Earth in the middle of our planet. It has a solid inner core and a liquid outer core.

Outer core[change | change source]

The outer core of the Earth is a liquid layer about 2,266 kilometers thick. It is made of iron and nickel. This is above the Earth's solid inner core and below the mantle. Its outer boundary is 2,890 km (1,800 mi) beneath the Earth's surface. The transition between the inner core and outer core is approximately 5,150 km beneath the Earth's surface.

The temperature of the outer core ranges from 4400 °C in the outer regions to 6100 °C near the inner core. 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.[1][2]

The outer core is not under enough pressure to be solid, so it is liquid even though it's mostly made of the same stuff as the inner core. Sulfur and oxygen could also be in the outer core.

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.[3][4] This magnetic field extends outward from the Earth for several thousand kilometers, and creates a protective bubble around the Earth that deflects the Sun's solar wind. Without this field, the solar wind would directly strike the Earth's atmosphere. This might have removed the Earth's atmosphere, making the planet nearly lifeless. It may have happened to Mars.[5]

Inner core[change | change source]

The inner core of the Earth, as detected by seismology, is a solid sphere about 1,216 km (760 mi) in radius, or about 70% that of the Moon. It is believed to be an ironnickel alloy, and may have a temperature similar to the Sun's surface, approximately 5778 K (5505 °C).[6]

In 2015 a Chinese scientist suggested the inner core has two layers.[7] The seismic wave data suggests that crystals in the "inner inner core" are in an east-to-west direction. Those in the "outer inner core" are lined up north to south. Another scientist commented: "If this is true, it would imply that something very substantial happened to flip the orientation of the core to turn the alignment of crystals in the inner core north-south as is seen today in its outer parts".[7] Other scientists are checking their data.

References[change | change source]

  1. Bruce A. Buffett 2010. Tidal dissipation and the strength of the Earth’s internal magnetic field. Nature 468, 952-954. doi:10.1038/nature09643
  2. http://www.nature.com/nature/journal/v468/n7326/full/nature09643.html
  3. Woodrow L. Shew, Daniel P. Lathrop 2005. Liquid sodium model of geophysical core convection. Physics of the Earth and Planetary Interiors 153 136–149
  4. Kent C. Condie 1997. Plate tectonics, Butterworth-Heinemann; 4th ed. p140 ISBN 978-0750633864
  5. http://scign.jpl.nasa.gov/learn/plate1.htm
  6. E.R. Engdahl; E.A. Flynn and R.P. Massé (1974). "Differential PkiKP travel times and the radius of the core". Geophys. J. Royal Astr. Soc. 39: 457–463. doi:10.1111/j.1365-246X.1974.tb05467.x .
  7. 7.0 7.1 Morelle, Rebecca 2015. Heart of Earth's inner core revealed. BBC News Science & Environment. [1]