A group of researchers from the University of Rochester, New York (USA), has been able to reconstruct the evolution of the Earth’s deep core over hundreds of millions of years by analyzing ancient rock crystals and the records of magnetism that are stored in them.
paleomagnetic research
The study suggests that Earth’s solid inner core – a hot, compact mass of iron and nickel – formed 550 million years ago and restored our planet’s magnetic field. Spinning liquid iron in the Earth’s outer core, many kilometers below ground (more than 2,500 km), generates our planet’s protective magnetic field; It is what we know as the magnetosphere.
We cannot see it, it is invisible to our eyes, but thanks to it there may be life on the surface of the Earth. This is because the magnetosphere protects the planet from the solar wind, the currents of radiation from the sun. However, about 565 million years ago, the strength of the magnetic field was reduced to 10% of its current strength. It almost collapsed, scientists say. This almost complete collapse of the magnetic field began early in the Cambrian period. Fortunately for us, and in an unknown way, the magnetic field woke up again, regaining its strength just before the Cambrian explosion of multicellular life on Earth.
Scientists rely on rock crystals, in this case the feldspar crystals in anorthosite (igneous rock) , to indirectly study the Earth’s core because it would be nearly impossible to do so due to great distances and extreme temperatures. In either case, these crystals serve as extremely accurate loggers of magnetism.
Thanks to this examination, they were able to determine the change in magnetic force, separating the innermost inner core from the outermost.
What caused this recovery of the magnetic field?
According to the research, published in the journal Nature Communications, this rejuvenation occurred within a few tens of millions of years, quite fast on geological time scales, and coincided with the formation of the Earth’s solid inner core, suggesting that the core is probably the direct cause of this new awakening of the magnetosphere.
“The inner core is tremendously important,” says John Tarduno, William R. Kenan, Jr., professor of geophysics in the Department of Earth and Environmental Sciences and dean of arts, sciences and engineering research at the University of Rochester. “Just before the inner core started to grow, the magnetic field was about to collapse, but as soon as the inner core started to grow, the field regenerated .”
Geological summary:
550 million years ago – time when the magnetic field began to rapidly renew itself after a near collapse 15 million years earlier. The molten outer core recharged and restored the strength of the magnetic field.
450 million years ago: time when the structure of the growing inner core changed, marking the boundary between the innermost and outermost inner core. These changes coincide with almost concurrent changes in the structure of the overlying mantle, due to plate tectonics at the surface.
“Because we constrained the age of the inner core more precisely, we were able to explore the fact that the current inner core is actually made up of two parts,” Tarduno said. ” Tectonic plate movements on the Earth’s surface indirectly affected the inner core, and the history of these movements is imprinted deep within the Earth in the structure of the inner core.”
Reference: “Early Cambrian renewal of the geodynamo and the origin of inner core structure” by Tinghong Zhou, John A. Tarduno, Francis Nimmo, Rory D. Cottrell, Richard K. Bono, Mauricio Ibanez-Mejia, Wentao Huang, Matt Hamilton, Kenneth Kodama, Aleksey V. Smirnov, Ben Crummins and Frank Padgett III, 19 July 2022, Nature Communications.
DOI: 10.1038/s41467-022-31677-7
