(ORDO NEWS) — More than half a billion years ago, the Earth experienced an almost complete disappearance of the magnetic field. It began in the early Cambrian period. Then, about 15 million years later, the field began to recover again.
The reason for this collapse and restoration of the field has been a mystery. A team of geologists then studied rocks from Oklahoma that had been created during that time.
Magnetic marks in the minerals of the rocks pointed to an event that began about 550 million years ago. This was before the advent of multicellular life on our planet.
According to John Tarduno, professor of geophysics at the University of Rochester in New York, the formation of the solid inner core of the Earth was the cause.
“The inner core is extremely important,” he said. “Right before the inner core started to grow, the magnetic field was on the verge of breaking down, but as soon as the inner core started to grow, the field was restored.”
In their article, Tarduno and a group of researchers cited the most important dates in the history of the inner core. They also gave an accurate estimate of the age of collapse and regeneration.
Since they cannot penetrate the core and directly observe it, how did they find out when these events occurred? To find the answer, the team turned to the field of paleomagnetism.
This is a study of magnetic markers in rocks that were created when the rocks formed. Geologists often use this to track records of other changes in the Earth’s magnetic field, such as a reversal of the poles.
The Earth’s magnetic field extends from the core through the mantle and crust into space. It is impossible to measure the magnetic field inside the Earth directly. This is due to the location and extreme temperatures of the materials in the core.
So geologists came up with a better way. They looked for paleomagnetic markers in rocks and minerals that had risen to the surface.
These marks are like tiny needles that record the direction and intensity of the magnetic field that existed when the minerals cooled after being formed.
Tarduno and his team wanted to accurately determine the age and height of the Earth’s inner core, using paleomagnetism to measure these particles.
So, they used a CO2 laser and a superconducting quantum interference device (SQUID) magnetometer to analyze anorthosite feldspar crystals and study their ideal magnetic markers.
By studying the magnetism contained in these ancient crystals, the researchers identified two important new dates. The first occurred when the magnetic field began to strengthen after the near-total collapse 15 million years ago.
This rapid recovery was due to the formation of a hard inner core. This effectively 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. Far above the core, there have been changes in the mantle due to plate tectonics at the surface.
According to Tarduno, paleomagnetism has provided more information about the Earth’s core.
“Because we have more accurately determined the age of the inner core, we have been able to explore the fact that the modern inner core is actually two parts,” he said.
“Tectonic plate movements on the Earth’s surface have indirectly affected the inner core, and the history of these movements is etched deep inside the Earth in the structure of the inner core.”
The study also provides insight into how the Earth 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 did not have magnetic fields.
For example, Mars once had a magnetic field, but it disappeared over 4 billion years ago. This left the planet vulnerable to the solar wind and likely played a role in the loss of the Martian oceans.
It is unclear whether the Earth would have suffered the same fate if its magnetic field had not recovered. Tarduno said that our planet would lose a lot of water if the magnetic field did not return.
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