A surprising observation has recently highlighted a close relationship between our planet's magnetic field and the oxygen content of its atmosphere.
Over more than half a billion years, these two parameters appear to have evolved in concert, revealing a connection between Earth's depths and surface conditions. Published in
Science Advances, this discovery suggests that Earth's habitability might be influenced by internal processes over long timescales.
To reach these findings, NASA scientists examined geological records covering nearly 540 million years. They compared fluctuations in the magnetic field, recorded in magnetic minerals, with changes in atmospheric oxygen, inferred from the chemistry of rocks. The team sought to identify common trends, which revealed impressive correlations between these two essential elements.
Earth's magnetic field is generated by currents of molten iron in the outer core. Like a giant dynamo, this internal activity produces a shield that protects the atmosphere from energetic particles emitted by the Sun. Changes in this field over the eons could thus affect the retention of gases, offering a possible link to the measured oxygen levels.
Evidence of this distant past is preserved in rocks. When magma cools, the minerals it contains trap the orientation of the surrounding magnetic field. In parallel, the chemical composition of sediments reflects the amount of oxygen present during their deposition. Thanks to databases compiled by geophysicists and geochemists, these traces could be analyzed on a vast timescale, allowing the reconstruction of the history of Earth's atmosphere and magnetism.
The observed correlation dates back to the Cambrian explosion, an era when complex life began to diversify on Earth. Researchers propose that phenomena like plate tectonics could be at the origin of this synchronization, acting on both the planet's interior and the atmosphere. Thus, this pivotal period in biological evolution appears linked to deep geological dynamics.
Looking ahead, the team plans to study even older periods and other important elements, such as nitrogen. Understanding the precise mechanisms that link Earth's core to surface conditions will require further investigation, but this line of inquiry opens new avenues for exploring the evolution of life on our planet.