Roughly 1,800 miles below our feet, the spinning of liquid iron in Earth’s outer core is generating our planet’s protective magnetic field. This magnetic field is invisible but vital to life on Earth because it protects the planet from the solar wind – streams of radiation from the sun.
About 565 million years ago, the strength of the magnetic field decreased to 10% of its strength today. Then, mysteriously, the field bounced back, regaining its strength before the Cambrian explosion of multicellular life on Earth.
What caused the magnetic field to bounce?
According to new research by scientists at the University of Rochester, this regeneration occurred within a few tens of millions of years — fast on geological time scales — and coincided with the formation of Earth’s solid inner core, suggesting that the core is likely a direct cause.
“The inner core is very important,” says John Tarduno, professor of geophysics in the Department of Earth and Environmental Sciences and dean of arts, sciences and engineering research at Rochester. “Just before the inner core started growing, the magnetic field was about to collapse, but as soon as the inner core started growing, the field was renewed.”
In the paper published in Nature CommunicationsIn this article, the researchers identified several key dates in the history of the inner core, including a more accurate estimate of its age. The research provides clues about the history and future development of Earth and how it became a habitable planet, as well as the evolution of other planets in the solar system.
Unlock the information in the ancient rocks
The Earth is made up of layers: the crust where life exists; the mantle, the earth’s thick layer; The molten outer core and the solid inner core, which in turn consists of an outer inner core and a deeper inner core.
Earth’s magnetic field is created in its outer core, where the rotation of liquid iron causes electric currents, resulting in a phenomenon called geodynamo that produces the magnetic field.
Because of the magnetic field’s relationship to the Earth’s core, scientists have been trying for decades to determine how the Earth’s magnetic field and core changed throughout the history of our planet. They cannot directly measure the magnetic field due to the location and extreme temperatures of the materials in the core. Fortunately, minerals that rise to Earth’s surface contain tiny magnetic particles that lock in the direction and intensity of the magnetic field as the minerals cool from their molten state.
To better restrict the lifespan and growth of the inner core, Tarduno and his team used carbon dioxide2 In vitro laser and superconducting quantum interference device (SQUID) to analyze feldspar crystals from anorthosite rocks. These crystals have tiny magnetic needles inside that are “ideal magnetic recorders,” Tarduno says.
By studying magnetism trapped in ancient crystals – a field known as palaeomagnetism – researchers have identified two important new dates in the history of the inner core:
- 550 million years ago: The time when the magnetic field began to regenerate rapidly after a collapse approximately 15 million years before that. The researchers attribute the rapid regeneration of the magnetic field to the formation of a solid inner core that recharges the molten outer core and restores the strength of the magnetic field.
- 450 million years ago: The time when the structure of the growing inner core changed, indicating the boundary between the inner and outer core. These changes in the inner core coincide with changes at about the same time in the upper shelf structure, due to plate tectonics at the surface.
“Because we constrained the age of the inner core more precisely, we can explore the fact that the current inner core is actually made up of two parts,” Tarduno says. “The movements of the tectonic plates on the Earth’s surface indirectly affected the inner core, and the history of these movements is imprinted deep inside the earth in the structure of the inner core.”
Avoid a Martian-like fate
A better understanding of the dynamics and growth of the inner core and magnetic field has important implications, not only in revealing Earth’s past and predicting its future, but also in revealing the ways in which other planets may form magnetic shields and maintain the conditions necessary to harbor life.
Researchers believe that Mars, for example, once had a magnetic field, but that field dissipated, leaving the planet vulnerable to the solar wind and a surface without oceans. While it’s unclear whether the absence of a magnetic field would cause Earth to meet the same fate, “Earth would certainly have lost a lot of water if Earth’s magnetic field had not been renewed,” Tarduno says. “The planet will be much drier and different from the planet today.”
Regarding the evolution of planets, the research underscores the importance of the magnetic shield and a mechanism for its preservation, he says.
“This research really highlights the need for something like a growing inner core that maintains a magnetic field for the lifetime – several billion years – of a planet.”
New research provides evidence of a strong early magnetic field around Earth
Tinghong Zhou et al, Early Cambrian renewal of the geodynamo and the origin of the internal infrastructure, Nature Communications (2022). DOI: 10.1038 / s41467-022-31677-7
Presented by the University of Rochester
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