Magnetic field protected already early earth

Astonishingly high field strength already 3.2 billion years ago

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Contrary to previous assumptions, the Earth's magnetic field was already as strong as it was now even 3.2 billion years ago. This is shown by a new study, now published in Nature . It also gives the first indications that the solid inner iron core of the Earth could also have existed much earlier than assumed.

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The importance of an intact, strong magnetic field lies above all in its protective effect against the harmful and eroding cosmic rays of the solar wind. They hit a planet almost unchecked, they not only decompose the atmosphere but kill off everything that is on the surface. Mars, which lost its magnetic field early in its history, is a typical example. The earth, on the other hand, escaped this fate as the interplay between the solid inner and the liquid outer core of the Earth created and continues to sustain a magnetic field.

Searching for clues in the rock

So far, however, it was unclear exactly when the solid inner core of the Earth formed and thus set the magneto dynamo in motion. Although data from very old rocks gave indications of the existence of a magnetic field, they seemed rather to indicate a very weak field, only about one-tenth as strong.

Geophysicists at the University of Rochester, led by John Tarduno, have now used a new method to move magnetic measurements, which had previously only reached 2.5 billion years, to over three billion years. While previously, whole rock samples were heated in the laboratory to determine their magnetic properties, the researchers now performed the analysis using individual quartz and feldspar crystals from a 3.2-billion-year-old granite block in Africa. These crystals are considered good "magnetic archives" because they preserve very well the strength and orientation of the field at the time of their formation. display

Inner core already 3.2 billion years ago

Using a laser beam and a so-called "SQUID" sensor - short for "Superconducting Quantum Interface Device", a sensor that is normally used in chip manufacturing, they were the first to accurately determine the magnetic intensity in a rock of this age. "The intensity of the prehistoric magnetic field was very similar to that of today, " explains Tarduno. "The data suggest that the field was surprisingly strong and robust. This is interesting because it could mean that the Earth already had a solid inner core 3.2 billion years ago - a time of creation that is quite at the limit of the previous models. "

To make sure that the values ​​were not altered by subsequent heating of the rock and thus falsified, the researchers also compared the preserved in the crystals orientation of the magnetic field with that of other rocks of this age. Since they agree, this confirms that the measured values ​​actually came from the time of 3.2 billion years ago. "The data suggest that the magnetic field strength was at least 50 percent of the current field of 40 to 60 microtesla, " explains Tarduno. "That means the Earth was already shielded by a magnetic field 3.2 billion years ago."

(University of Rochester, 05.04.2007 - NPO)