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Some studies believe that the earth's rotation axis changed greatly from late Neoproterozoic to early Cambrian, and the geographical movement of the north and south poles led to dramatic changes in the living environment on the surface, which contributed to the outbreak of life in the Cambrian. However, new research shows that the earth may not be spinning at that time, but the earth's magnetic field rotates violently.

Wen Jing | Wen Jing

The geomagnetic field is generated by the movement of matter in the earth's core and extends through the surface to outer space to protect life on Earth from solar wind and high-energy cosmic rays. In the history of the earth, the birth of the core has caused a great disturbance to the geomagnetic field. New research shows that the Cambrian life explosion is related to the change of magnetic field at that time.

The geomagnetic field of the earth's core from scratch is produced by the magnetic material flowing in the core, which is mainly in the outer core, while the core is a solid iron ball. The geomagnetic field can resist the erosion of the atmosphere by the solar wind and block high-energy cosmic rays, thus protecting the creatures living on the earth's surface. Like Earth's "good brother" Mars, there is no magnetic field protection, its core is a completely solidified state, there is no magnetic material flow, therefore, we can not observe the signs of life on Mars.

The solid core of the earth has gone through a process from scratch, and now it is still growing, and may eventually be completely solidified, but that is too far away for mankind, so we do not have to worry about facing the predicament of Mars. For more information, please poke: is the core solidifying rapidly? Will Earth become as lifeless as Mars?)

Reviewing the history of the earth, we can say that the evolution of the geomagnetic field plays an important role in the origin and evolution of life on the earth.

It is generally believed that the solid core of the earth began to appear in the late Neoproterozoic-that is, before the arrival of the Cambrian-and then continued to grow and grow to its present size. Scientists think so because paleomagnetic evidence shows that the polarity of the geomagnetic field reverses frequently in the late Neoproterozoic and is the lowest in existing records.

Scientists infer that during the initial formation of the solid core, great changes have taken place in the structure of the earth's core, which disturbed the original geomagnetic field, resulting in frequent reversal of geomagnetic polarity, weakening of magnetic field and so on.

The true pole shift contributed to the Cambrian explosion of life? The instability caused by the initial formation of the core is obviously disadvantageous to the biological evolution on Earth. Since then, the geomagnetic field has experienced a process of returning from an unstable state to a relatively stable state, and scientists have been exploring this recovery mechanism and how the recovery process affected the Precambrian-Cambrian biological evolution.

It is believed that during the early Cambrian (the farthest of the three Cambrian periods, the closest to the late Neoproterozoic), a true pole shift with an amplitude of about 90 °occurred on the earth, which was an important reason for the outbreak of life in the Cambrian.

The true pole shift means that due to the change of the mass distribution of various parts of the earth, the solid layer outside the earth (including the crust and the upper mantle) rotates relative to the inner circle, which further leads to the change of the earth's rotation axis and the location shift of the south and north poles. The true pole shift of 90 °is equivalent to the original pole reaching close to the equator.

Scientists who support this view believe that the true pole shift has caused great changes in the latitude positions of the earth's land and oceans, as well as significant fluctuations in sea levels, further affecting the surface environment on which organisms live. It has even led to the reorganization of climatic zones and ecosystems, and these changes have accelerated the evolution of life on Earth.

Geomagnetic pole change rather than rotation axis change? Recently, a study published in Nature Communications questioned the idea that the true pole shift contributed to the Cambrian explosion of life.

In the new study, a team led by Professor Li Yongxiang of Nanjing University studied the geomagnetic pole changes in the late Cambrian, the most recent of the three Cambrian periods. The results show that at that time, the Earth's magnetic poles may have wobbled rapidly, with an amplitude of about 90 °, but only lasted about 80,000 years.

If we want to compare 90 °true pole shift and 90 °geomagnetic pole swing, the characteristics of them are very similar, and the judgment of true pole shift and geomagnetic pole swing depends on the study of paleomagnetism. The difference is that the earth cannot have such a large true pole shift in such a short time (80,000 years).

The wobble of the geomagnetic poles can also have an impact on life on Earth, but the changes are relatively modest. Moreover, on the earth at that time, animals that rely on geomagnetic field for migration and human beings who make use of electromagnetic effects to carry out various production and life activities have not yet appeared, so the impact of geomagnetic field changes may be more limited.

When did the geomagnetic field stabilize? In the new study, scientists also infer that the earth's core may not have become large enough from the beginning of its birth to the late Cambrian, thus disturbing the geomagnetic field. However, the geomagnetic field did not stabilize until the late Cambrian to early Ordovician. At the same time, the marine biodiversity and marine oxygen content of the earth increased, and the earth also appeared the Phanerozoic (from Cambrian to the present; different from the previous Pterozoic, Archean and Proterozoic, there were more life activities in this period).

Scientists believe that during the Cambrian, the earth's rotation was stable. However, even if the dimension of the earth does not change greatly and rapidly, the process of the recovery of the geomagnetic field from the disturbance caused by the birth of the core has promoted the evolution of life on Earth to a certain extent. so that biodiversity can be greatly improved during this period.

References:

Late Cambrian geomagnetic instability after the onset of inner core nucleation | Nature Communications

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