How did Earth avoid a Mars-like fate? Ancient rocks hold clues

Our planet's protective magnetic field is generated by the swirling iron in the Earth's outer core. The magnetic field is invisible but vital for life because it protects the planet from solar wind.

The magnetic field's strength went down to 10 percent. The field regained its strength just before the explosion of multicellular life on Earth.

The magnetic field bounced back.

The rejuvenation happened within a few tens of millions of years and coincides with the formation of Earth's solid inner core, according to new research from the University of Rochester.

The dean of research for Arts, Sciences and Engineering at Rochester says the inner core is important. The magnetic field was at the point of collapse before the inner core began to grow.

The researchers estimated the age of the inner core in a paper published in Nature Communications. Clues about the history and future evolution of Earth are provided by the research.

Information can be found in ancient rock.

The solid inner core is composed of an innermost inner core and an outer inner core.

The Earth's magnetic field can be found in its outer core, where the swirling liquid iron causes electric currents.

Scientists have been trying to understand how Earth's magnetic field and core have changed over time. The magnetic field can't be directly measured due to the extreme temperatures of the materials. At the time the minerals cool from their molten state, they contain tiny magnetic particles that lock in the direction and intensity of the magnetic field.

To better understand the age and growth of the inner core, Tarduno and his team used a CO 2 laser and a SQUID magnetometer. Tarduno says that these crystals are perfect magnetic recorders.

The researchers were able to determine two important dates in the history of the inner core by studying the magnetism locked in ancient crystals.

• 550 million years ago: the time at which the magnetic field began to renew rapidly after a near collapse 15 million years before that. The researchers attribute the rapid renewal of the magnetic field to the formation of a solid inner core that recharged the molten outer core and restored the magnetic field's strength.
• 450 million years ago: the time at which the growing inner core's structure changed, marking the boundary between the innermost and outermost inner core. These changes in the inner core coincide with changes around the same time in the structure of the overlying mantel, due to plate tectonics on the surface.

Tarduno says that they were able to explore the fact that the present-day inner core is actually composed of two parts. The history of plate tectonic movements on Earth's surface can be seen in the inner core.

It's possible to avoid a fate like Mars.

Understanding the dynamics of the inner core and the magnetic field can have important implications, not only in uncovering Earth's past and predicting its future, but in unraveling the ways in which other planets might form magnetic shields and sustain the conditions necessary to harbor life.

Mars is vulnerable to solar wind and the surface without oceans because it once had a magnetic field, according to researchers. Earth would have lost more water if the magnetic field hadn't been regenerated. The planet would not be the same as it is now.

The importance of a magnetic shield and a mechanism to sustain it is emphasized in the research.

The need for a growing inner core that sustains a magnetic field over the lifetime of a planet is highlighted by this research.

More information: Tinghong Zhou et al, Early Cambrian renewal of the geodynamo and the origin of inner core structure, Nature Communications (2022). DOI: 10.1038/s41467-022-31677-7 Journal information: Nature Communications