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Earth's magnetic field almost died during a critical transition

Earth's magnetic field almost died during a critical transition

You have almost certainly seen a diagram — the layers of the Earth were exposed as a slightly more complex hard boiled egg. The crust on which we live is actually a thin shell, under which the hot (but still hard) mantle forms a thick layer. In the center – against Jules Verne – there are inner and outer layers of the nucleus, consisting mainly of iron. The outer core is the only layer that is liquid, as the inner core is actually solid.

Although you will never visit the core, it will really greatly affect your life. Earth's magnetic field is created by convection of the liquid external core, which directs the compasses and protects us from the effects of the solar wind. The history of the Earth’s magnetic field is a big question – not least because we’re not really sure when the inner core has hardened.

Magnets … well, you know

There are in fact, geological records of the magnetic field. The tiny crystals of magnetic minerals in the cooling magma will align with the magnetic field before freezing in place. This can be useful because the Earth’s magnetic field often turns over the poles (i.e., the needles of the compass will point to the geographic south). The orientation of these mineral needles also indicates how close they were to the equator when they formed. The information trapped in these minerals was the last part to reveal the fact of plate tectonics, in fact, and it allows us to figure out where each continent was in the past.

We can also determine how strong the magnetic field was from these records. This is what the team, led by Richard Bono and John Tarduno of the University of Rochester, was most interested in when they analyzed about 565 million years of breed in Quebec.

We do not have much data for that period of time, which some researchers suspect could be when the inner core finally began to strengthen. In this case, the igneous rocks the researchers worked with slowly cooled underground, which means their records probably cover about 75,000 years. This should be longer than usually requires a reversal of the magnetic poles, so any temporary changes like this should be averaged.

Weak sauce

The team discovered that the magnetic field was incredibly weak at the time of the study. The Late Jurassic period is characterized by an abnormally weak magnetic field, but it was about one-fifth stronger than this time period. In addition, it seems that the magnetic poles turned upside down very often. This is a very strange behavior.

These data actually correspond to the limited information that we have for the periods closest to this time, which is also rather strange. And the research becomes really interesting when you compare it with modeling the history of the core of the Earth. Some of these simulations predict that the solidification of the inner core was relatively recent geologically and occurred around this time. In these models, the reorganization of the nucleus makes the magnetic field doze for a while, spinning in a weakened state.

Researchers say that their evidence corresponds to the scenario when the inner core only began to strengthen about 565 million years ago – almost 4 billion years in the life of the Earth. This adds to the question of how the “geodynamo” in the core, producing a magnetic field, looked like before this time and how it lasted for so long. It also adds to the crowded list of weird things that happened in this chapter of the history of the Earth, which includes a remarkable evolutionary explosion of complex animal life.

The summary accompanying the document in Nature studyPeter Driscoll, a researcher at the Carnegie Institute of Science (who did not participate in the study) outlines the work necessary to continue this juicy hypothesis: . Experiments on the solidification and conductivity of iron will further limit the thermodynamics of the core. Finally, numerical models of the evolving nucleus can produce detailed predictions that check how all these components are combined. ”

And if this timeline for the formation of the inner core is correct, Driscoll writes, “the nucleation of the inner core could have happened just at the last moment to recharge geodynamics and save the Earth’s magnetic shield.

Nature study, 2019. DOI: 10.1038 / s41561-018-0288-0, 10.1038 / s41561-019-0301-2 (О DOI).

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