Earth’s Magnetic Field Almost Completely Collapsed 550 Million Years Ago
More than half a billion years ago, the Earth experienced an almost complete collapse of its magnetic field. It started at the beginning of the Cambrian period. Then, after a period of about 15 million years, the field began to grow again. The cause of this collapse and rebound of the field was a mystery. Then a group of geologists studied the rocks in Oklahoma that were created at that time. Magnetic markers in rock minerals indicated an event that began about 550 million years ago. This was before the introduction of multicellular life on our planet.
Look deep into the core
To understand what happened, look at the structure of our planet. Most of us learn in school that the Earth is made up of layers. There’s the crust, where you’re sitting reading this right now. Below is the mantle, the thickest layer of the Earth. It rests on the molten outer core, which surrounds the solid inner core. This inner core has two parts: an outermost inner core and an innermost inner core. The central region lies about 2900 kilometers below the surface. The swirling action of liquid iron in the outer core is what generates our magnetic field. Without this activity, we would not have a protective shield against the solar wind. In fact, without it, our planet might look more like Mars today.
So what happened in the kernel? Why did our magnetic field fade to almost 10% of its strength and then regenerate again? According to John Tarduno, professor of geophysics at the University of Rochester in New York, the cause was the formation of the Earth’s solid inner core.
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“The inner core is extremely important,” he said. “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 regenerated.”
Paleomagnetism reveals changes in our magnetic field
In a recent paper, Tarduno and a team of researchers cited crucial dates in the history of the inner core. They also gave an accurate estimate of the age of collapse and regeneration. Since they cannot reach the core and observe it directly, how did they find out when these events happened? The team turned to paleomagnetism for an answer. It is the study of magnetic markers in rocks that were created during the formation of rocks. Geologists often use it to trace records of other changes in the Earth’s magnetic field, such as the pole shift.
The Earth’s magnetic field extends from the core through the mantle and crust and out into space. It is impossible to directly measure the magnetic field inside the Earth. This is due to the location and extreme temperatures of the materials in the core. So geologists thought of a better way. They looked for paleomagnetic markers in the rocks and minerals that rose to the surface. These markers are like tiny needles that lock in the direction and strength of the magnetic field that existed when the minerals cooled after they were formed.
Tarduno and his team wanted to determine the age and growth of the Earth’s inner core by using paleomagnetism to measure these particles. So, they used a CO2 laser and a superconducting quantum interference device (SQUID) magnetometer to analyze feldspar crystals from rock anorthosite and study their perfect magnetic markers.
Meet rocks using magnetism for victory
By studying the magnetism locked in these ancient crystals, researchers have determined two new important dates. The first was when the magnetic field began to strengthen after nearly collapsing 15 million years earlier. This rapid regrowth was due to the formation of a strong inner core. It actually recharged the molten outer core and restored the strength of the magnetic field.
Another interesting thing happened about 450 million years ago. It was then that the structure of the growing inner core changed. The result was a boundary between the innermost and outermost inner core. High above the core, mantle changes have taken place due to surface plate tectonics.
Paleomagnetism made this new understanding of the Earth’s core possible, according to Tarduno. “Because we limited 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,” he said. “Plate tectonic movements on the Earth’s surface have indirectly affected the inner core, and the history of these movements is imprinted deep within the Earth in the structure of the inner core.”
What about magnetic fields elsewhere?
The team’s research into paleomagnetic clues to Earth’s interior evolution provides clues to the history and evolution of our planet. It also offers insight into how it became habitable. Finally, their work has implications for understanding the evolution of other planets in the solar system. Things could be very different if they had no magnetic fields. For example, Mars once had a magnetic field, but it dissipated over 4 billion years ago. This made the planet vulnerable to the solar wind and likely played a role in the loss of the Martian oceans.
It is not clear if the Earth would have suffered the same fate if its magnetic field had not regenerated. Tarduno said our planet would have lost a lot of water if the magnetic field hadn’t returned. “The planet would be much drier and very different from today’s planet,” he pointed out. “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.”
For more information
How did Earth avoid a Mars-like fate? Ancient rocks hold clues
Early Cambrian renewal of the geodynamo and origin of the inner core structure