You've probably seen the diagram – the layers of earth are like a more complicated hard-boiled egg. The crust we live on is actually a thin shell. The hot (but still firm) coat forms a thick layer underneath. In the middle – in contrast to Jules Verne ̵
Although you will never visit the Core, it deeply affects your life. The earth's magnetic field is created by the convection of the liquid outer core. This guides the compass and shields us from the effects of the solar wind. The history of the Earth's magnetic field is a big question – not least because we are not sure when the inner core will freeze.
Magnets … Well, you know,
There are actually actual geological records of the magnetic field. Tiny crystals of magnetic minerals in cooling magma align themselves with the magnetic field before they freeze. This can be useful as the earth's magnetic field often turns poles around (ie, compass needles would point to the geographical south). The orientation of these mineral needles also indicates how close they were to the equator as they formed. The information captured by these minerals was the last piece that has actually broken the case of plate tectonics, and we can find out where each continent was in the past.
We can also figure out how strong the magnetic field was from these records. One of the most interested in this was a team from Richard Bono and John Tarduno at the University of Rochester, where they analyzed approximately 565 million year old rocks in Quebec.
We do not have much data from this period Some researchers suspect that the inner core has finally solidified. In this case, the igneous rocks the researchers worked on slowly cooled underground, meaning that their record is likely to be around 75,000 years. This should be longer than reversing the magnetic poles normally takes, so such transient changes should be averaged.
The team found that the magnetic field was incredibly weak at the time. The late Jurassic period is characterized by an unusually weak magnetic field, which was only about one fifth as strong as this period. In addition, the magnetic poles seem to turn extremely frequently. It is a very strange behavior.
This data actually fits the limited information we have from periods closest to that time, which is also quite strange. The study will be really interesting if you compare it with simulations of the history of the Earth's core. Some of these simulations have predicted that geological solidification of the inner core was relatively new and occurred at that time. In these models, reorganizing the nucleus causes the magnetic field to go wild for a while and wander around in a weakened state.
The researchers say that their evidence fits a scenario in which the inner core did not solidify until after about 565 million years ago, almost four billion years ago in the Earth's life. This raises additional questions as to how the magnetic field-producing "geodynamo" at the core looked before this time and how it lasted so long. It also adds the jam-packed list of weird things that went on in this chapter of Earth's history, which happens to include a remarkable evolutionary explosion of complex animal life. Geoscience The scientist of the Carnegie Institution for Science, Peter Driscoll (who does not involved in the study) explains the work that is needed to pursue this succinct hypothesis: "Additional paleomagnetic observations, both directions and intensities, are the next step to provide a clearer picture of the state of the nucleus around that time. Iron solidification and conductivity experiments will further limit the thermodynamics of the nucleus. Finally, numerical models of the evolving kernel can provide detailed predictions to test how all of these components fit together.
And if this timeline of the formation of the inner core is correct, Driscoll writes: "Nucleation of the inner nucleus may be punctual to recharge the geodynamo and rescue the earth's magnetic shield.
Nature Geoscience 2019. 0301-2 (via DOIs).