We know that the core of the Earth is made of iron and we may be tempted to think that it is a block like the ones we are used to seeing, but it is not. The answer may be even more surprising: Geophysicists at the Carnegie Institution of Washington have hinted that there may be a huge crystal at the center of the Earth .
It all started in 1995 when they discovered something amazing: seismic waves go about 4 seconds faster when they travel from pole to pole than when they travel across the equator. This means that the solid core of the Earth is anisotropic, that is, it does not have the same properties in all directions. Ronald Cohen of the Carnegie Institution of Washington explained the situation like this: “We know there is a certain type of structure but we don’t know what it is. Hence, he and his team set their sights on the CRAY C90 supercomputer at the Pittsburgh Supercomputing Center to try to understand what happens to our planet’s solid iron core.
Iron can appear on the surface in three distinct crystalline forms: centered cubic packing (cc), face centered cubic packing (ccc) and compact hexagonal packing (hc). Until now it was thought that the iron in the center of the Earth would be in the first form (cc), but the detailed calculations of the CRAY show that this crystalline structure cannot exist at those pressures and temperatures, but the other two can. Furthermore, the hexagonal packing of the iron is the one that best fits the seismic data.
But what is really surprising is that such a pronounced anisotropy can be caused by a single large iron crystal. The other explanation, that the nucleus is composed of myriads of crystals , has the disadvantage that to explain this anisotropy all the crystals must be oriented in the same direction.
Can a single huge crystal really exist in the center of the Earth? The proposal is so radical that different laboratories around the world try to see experimentally if it is possible.
