Early magnetic shield was stronger: The geomagnetic field, generated in the core of our planet, provides a shield against cosmic radiation, which can damage artificial satellites, electrical energy networks and the ozone layer. In the absence of this shield, the solar wind could gradually erode the atmosphere, and eventually leave the planet without water.
Our dipole magnetic field has diminished in strength during the last 160 years at an alarming rate, which has motivated an energetic debate about whether we are in the early stages of an inversion of the geomagnetic pole.
A group of researchers discovered evidence that our planet had a strong magnetic field 4.2 billion years ago, 750 million years earlier than previously thought and only 350 million years after the formation of the Earth. The research, published in PNAS , corroborates the theory that this magnetism protected the atmosphere of our planet from the highly energetic particles sent from the Sun – allowing life to develop.
“This research is telling us facts about the formation of a habitable planet,” said John Tarduno, one of the scientists, in a statement . “One of the questions we want to answer is why the Earth evolved as it evolved – and that gives us even more evidence that the magnetic shield was registered very early on the planet.”
Analyzing crystals for Early magnetic shield was stronger
Some even believe that we are late. But in geological terms, 160 years is just the blink of an eye. The record is too short to have great confidence about what these trends could mean in causal processes and the future.
In this sense, a team of researchers from the University of Rochester is trying to unravel the changes of the magnetic field throughout its history, an understanding that can provide clues about the future evolution of the Earth, as well as that of other planets.
To do this, the research team analyzed zircon crystals, the oldest known terrestrial materials collected in Australia. These crystals contain magnetic particles that show the magnetization of the Earth at the time they were formed.
The Earth’s magnetic field is generated in the core of the planet, thanks to the huge amount of liquid iron present there: the material moves, generating electric current and boosting magnestism. Due to the location and extreme temperatures of this material, scientists are not able to directly measure the planet’s magnetic field.
However, when some of these minerals reach the Earth’s surface – for volcanic activities , for example – they can be studied. That’s how Tarduno’s team was able to study small zircon crystals, one of the oldest minerals we know, found in Australia.
That’s because zircons, about two tenths of a millimeter, contain even smaller magnetic particles that store information about terrestrial magnestism from when the crystals were formed. It was by studying this material that Tarduno and his team concluded that when the Earth’s original rock (containing zircon) cooled for the first time, the magnetic field was created.
Although the researchers initially believed that the Earth’s initial magnetic field was weak, the new zircon data suggests a much higher intensity. However, as the core of our planet had not yet formed, this magnetism was probably the result of a phenomenon other than the movement of iron. “We think that this mechanism is the chemical precipitation of magnesium oxide”, pointed out Tarduno.
Previous research found that the Earth’s magnetic field is at least 4.2 billion years old, and that the inner core of the planet formed “only” 565 million years ago.
While the planet’s early magnetic field was initially thought to be weak, the analysis of zircon crystal data suggests a stronger field.
For the researchers, this is a controversial observation, since because the inner core had not yet formed, the strong intensity of the magnetic field revealed in the zircon crystals had to be driven by a different mechanism.
In this regard, researcher John A. Tarduno, a professor in the Department of Earth and Environmental Sciences at the University of Rochester and lead author of the study, said:
“We believe that mechanism is the chemical precipitation of magnesium oxide inside the Earth.”
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The researchers propose that this magnesium oxide may have spread in the atmosphere due to the intense heat produced by the impact that the Moon would eventually form, and that while the Earth’s interior cooled, the chemical compound precipitated on the Earth’s surface, driving the magnetic field strength.
While the source of magnesium oxide was depleted, to the point that the magnetic field collapsed almost completely, the formation of the inner core provided a new source of momentum to the geo dynamic and planetary magnetic shield that Earth currently has.
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