New research published in Thursday’s edition of the journal Science indicates that the Earth’s magnetic shield is far older than previously believed, which could mean that plate tectonics also started earlier and may explain why the planet is still habitable.
In the study, University of Rochester geophysicist John Tarduno and his colleagues report that their research has led them to conclude that the Earth’s magnetic field is more than four billion years old, not 3.45 billion years old, as previous estimates calculated in 2010 have claimed.
“A strong magnetic field provides a shield for the atmosphere,” protecting it from solar winds (streams of charged particles originating from the sun), Tarduno explained in a statement. “This is important for the preservation of habitable conditions on Earth,” as the magnetic field keeps the solar wind from stripping away the planet’s atmosphere and surface water.
The magnetic field is generated in the planet’s liquid iron core, and a steady release of heat is required for this “geodynamo” to operate. Today, plate tectonics assist with this heat release by transferring heat from the planet’s deep interior to the surface.
Findings may explain why Earth is still habitable (and Mars is not)
However, Tarduno said, the origins of plate tectonics are disputed, as some scientists believe that Earth did not have a magnetic field early on in its existence. Researchers have been attempting to determine how and when this magnetic field first arose, thus helping experts determine when and how plate tectonics began and how our homeworld was able to remain habitable.
The researchers looked at samples of a mineral known as magnetite, which records the magnetic field at the time they cooled from their molten state. The magnetite was obtained from zircon crystals collected from Western Australia, and they sampled zircon crystals of different ages and found evidence suggesting that the magnetic field is approximately 4.4 billion years old.
The measurements taken by Tarduno’s team reveal that the magnetic field likely helped protect the planet at a time when solar winds were 100 times stronger than they are today. Without it, he said, the protons that make up those solar winds would have ionized the atmosphere and caused the loss of the planet’s water – which may explain what happened to life on Mars.
Experts believe that Mars had an active geodynamo when it was formed, but that four billion years later, it had died off. As a result, the Red Planet lacked a magnetic field that could shelter the atmosphere from the solar winds, Tarduno explained. This could explain why Mars’ atmosphere is so thin, he added, as well as why the planet “was unable to sustain life.”
(Image credit: Michael Osadciw/University of Rochester)
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