The center of Earth, colder than expected

1993/12/01 Elhuyar Zientzia Iturria: Elhuyar aldizkaria

• Geologia

The temperatures of the Earth in the inner core, in the outer core, and in the lower mantle are unknown. Geophysics usually say that the border temperature between the inner core and the outer core is 7,500 °C, but they reach this figure with extrapolations. The inner core is solid, it is said, and the outer core that surrounds it, placed under the lower mantle, liquid.

These temperatures are obtained from a series of calculations in which two factors intervene: the pressure and nature of the melted materials. However, the melting temperature of iron that is part of the core at very high pressures and the influence of certain alloys of light elements in these temperatures is unknown.

R. R. Max Planck Institute of Mainz The scientist Boehler has indicated that these temperatures would be lower than the calculations made to date. Small amounts of iron and oxygen and iron compounds have been placed between the two diamond tips and have been heated with laser by pressing up to 2 million bars or 2 thousand hectopascales of pressure. As the pressure increases, temperatures are measured.

Underground, the limit of the solid and liquid core is 5.100 kilometers and the pressure is 3.3 Mbar. The essay, Mr. Boehler indicates that the melting temperature in these conditions is only 4.600 °C. The temperature limit between both cores is, therefore, 3.000 °C lower than expected.

The temperature on the surface of the outer core would be 3.700 °C, due to the lower pressure. Because the bottom of the silicate mantle is a few kilometers above, it would be at an approximate temperature of 2,400 °C.