Accurate measurements of the magnetization of the ancient rocks of the Earth on the Kola Peninsula helped Russian scientists to find out that the solid inner core of our planet was formed much later than geophysicists had previously believed. This was reported by the press service of the Institute of Physics of the Earth RAS.
In the distant past, the Earth's core was completely liquid, and did not consist of two or three, as some geologists today suggest, layers - the inner metal core and the surrounding melt of iron and lighter elements.
In this state, the core quickly cooled and lost energy, which led to a weakening of the magnetic field generated by it. After some time, this process reached a certain critical point, and the central part of the nucleus "froze", turning into a solid metal nucleolus. This was accompanied by a surge and growth in the strength of the magnetic field, as well as dramatic changes in the mechanism of its work.
The time of this transition is extremely important for geologists, as it allows us to roughly estimate how fast the Earth's core is cooling down today and how long the magnetic shield of our planet will last, protecting us from the action of cosmic rays, and the Earth's atmosphere from the solar wind.
While scientists do not have an accurate estimate of exactly when this happened - theoretical models predict that this could have happened both long ago, in the Archean era, about two billion years ago, and noticeably later, during the Proterozoic or even Ediacaran times, shortly before the Cambrian explosion”and the emergence of modern multicellular animals.
Veselovsky and his colleagues took a big step towards obtaining an accurate answer to this question by studying the properties of the so-called dolerite sills - horizontal layers of deep crustal rocks that "wedged" into its near-surface layers during large magma eruptions. The most striking examples of their existence can be found in the rocks of the famous East Siberian traps, which caused the Perm extinction, as well as on the Kola Peninsula.
The latter, as noted by Veselovsky and his colleagues, formed in the first half of the Proterozoic era, approximately 1.96-0.92 billion years ago. This gave Russian scientists the opportunity to study the state and properties of the Earth's magnetic field in that geological epoch by measuring the residual magnetization of rocks mined on the seashore in the northern part of the Murmansk region.
In them, as scientists have found, preserved sufficiently high-quality and unambiguous traces of the ancient magnetic field of the Earth, which allowed them to calculate the position of its poles and the strength of about 1.86 billion years ago, as well as follow its "migrations" in previous and subsequent eras, using other ancient samples of bark rocks.
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In addition, scientists calculated the position of the Kola Peninsula at that time - it was in subtropical latitudes and was "rotated" 25 degrees in relation to its current configuration.
These measurements showed that the magnetic field was relatively weak at that time, but its position remained almost unchanged. Both confirms the popular theory that the Earth's magnetic field was relatively weak before the solid part of the core "solidified", and at the same time indicates that this did not occur until the middle of the Proterozoic.
Russian scientists suggest that it appeared much later, during the Ediacaran era, since many measurements of the strength of the magnetic field that reigned on Earth about 1.5 billion years ago could be greatly overestimated. In addition, these abnormally high values may indicate that its tension may have fluctuated strongly up and down until the nucleolus was formed.