We know that the magnetic fieldmagnetic field which protects us from harmful cosmic radiation has existed for a long time. A recent study has also shown that it already existed 3.7 billion years ago and that its intensity was relatively strong. The early establishment of a strong magnetic field is suspected of having played a role in the emergence of life. Much later, the presence of this invisible magnetic shell would also have allowed primitive organisms to leave the protection of the oceans and venture onto dry land.
Unexplained drops in magnetic field intensity
Since then, despite its small fluctuations and its numerous polarity reversals, the magnetic field has remained generally stable. However, there are some accidentsaccidents » whose origin is not yet understood, during which the intensity of the magnetic field decreased dramatically. Earth’s geological records reveal that around 360 million years ago, the magnetic field weakened to the point where it could no longer be correctly recorded in the magmatic rocks produced at that time. An exceptional situation fortunately short durationdurationwhich would not, however, have threatened terrestrial life, even if scientists note that at this time, plants beginning to colonize the terrestrial environment would have suffered abnormally high rates ofUVUV-B, radiations usually blocked by magnetospheremagnetosphere.
But this anomalyanomaly However, the magnetic field of the Devonian would not be the only one to have marked the history of the Earth. Much earlier, 591 to 565 million years ago, the magnetic field experienced a totally unusual drop in intensity. We are then at the end of the Neoproterozoic, and more precisely at the Ediacaran period. Life, already well established in the Earth’s oceans, has not yet invaded the land surface and appears in the form of very primitive organisms with soft bodies. At first glance, the wobble of the Earth’s magnetic field at this time does not seem to have impacted this relatively simple and only marine life, the water making it possible to block the more intense cosmic radiation then striking the Earth’s surface.
A weakness of the magnetic field coinciding with a diversification of living things
Things could have stayed there, except that by looking closely at this period of Earth’s history, a team of researchers noticed some major coincidences of events. The registers fossilsfossils indicate in fact that organisms experienced significant complexity and diversification, between 575 and 565 million years ago. Previous studies have suggested that this evolutionary episode was caused by a significant increase in oxygen levels in the oceans and atmosphere. An upheaval in environmental conditions that is often associated with the saturation of oxygen wells, which until then “stored” the dioxygen produced by photosynthetic organisms in the form of oxides (of ironiron notably). When all the elements capable of being oxidized would have been, we would have witnessed a drastic and rapid increase in free oxygen in theatmosphereatmosphere.
However, it is not clear whether the saturation of oxygen wells is the sole cause of this unprecedented oxygenation of the Earth. And the coincidence with the virtual disappearance of the magnetic field at this same moment made scientists tick.
Could there indeed be a link between these two events? Yes, according to Wentao Huang and John Tarduno of the University of Rochester (United States), main authors of an article published in the journal Communications Earth and Environment.
An increase in oxygen concentration linked to the loss of hydrogen in space
The analysis of tiny plagioclase crystals having recorded the characteristics of the magnetic field during the Ediacaran reveals that the magnetic field reached its lowest intensity in all of Earth’s history during this period. About 30 times less than the current intensity! This situation would have lasted at least 26 million years. However, this virtual absence of magnetic field could have allowed thehydrogenhydrogen to escape into space, thus increasing the percentage of oxygen in the atmosphere.
Hydrogen is in fact a very light element, which mainly forms part of the composition of the outermost layers of the atmosphere (ionosphereionosphere). If usually these layers are protected from erosion of solar windssolar winds by the magnetosphere, scientists show that 591 to 565 million years ago, this would not have been the case. Subjected to the “abrasive” action of cosmic particles, hydrogen would therefore have escaped in massmass during this period, participating in the rapid oxygenation of the atmosphere.
It could therefore be that via This process of atmospheric erosion, the drastic drop in the intensity of the magnetic field during the Ediacaran, favored the diversification of living organisms, a major stage in the history of terrestrial life.
