Deep within our planet, in the inner core, vortexes of liquid iron produce our magnetic field, an invisible shield that protects all life from the incredible solar winds. Knowing more about the magnetic field can provide us with clues to understand the future evolution of the Earth, as well as that of other planets in the solar system. If the magnetic field did not exist, the flow of high-energy particles from the Sun would destroy the ozone layer and with it the possibility of life on Earth and our landscape would look a lot like the desert Mars, where the old magnetic field collapsed when the planet cooled and the core stopped spinning.
How did they discover that the early magnetic field was so strong?
Thanks to small crystals found in rocks in Australia (rocks more than half a billion years old), which are helping scientists unravel the ancient history of our planet’s first magnetic field, which disappeared hundreds of millions of years ago . These crystals show that this shield, originated some 350 million years after Earth was formed, was much more powerful than previously thought , a mystery that could help answer the question of how life arose here. And it is that this magnetic field would have protected the Earth, its atmosphere, from the high-energy particles of the sun, and perhaps helping life to take hold.
We are talking about a stage known to geologists as the Hadic or Hadeic eon , which lasted from 4,550 million years to 4,000 million years ago – of which there are fragmentary clues in rocks in the Jack Hills area of Western Australia. These rocks contain tiny crystals of a mineral called zircon, the oldest known terrestrial material. The experts, using new paleomagnetic and geochemical data, together with electron microscopes, dated and analyzed these zircon crystals of about two tenths of a millimeter, in whose magnetic particles the magnetism of the Earth was recorded at the moment in which the magnetism was formed. mineral.
“This research tells us something very important about the formation of a habitable planet”, clarifies John Tarduno, geophysicist at the University of Rochester, New York (USA) and leader of the work collected by PNAS magazine. “One of the questions we want to answer is why the Earth evolved the way it did, and this work offers us even more evidence that the Earth’s magnetic shielding was recorded on the planet very early on.”
What drove the magnetic field?
However, the core of the Earth had not yet formed. It was formed only 565 million years ago . Then? The early magnetic field must have been driven by a different mechanism. What was it
“We think that this mechanism is the chemical precipitation of magnesium oxide within the Earth, ” Tarduno said.
Magnesium oxide, which had dissolved in the fully liquid core during the same impact that created our Moon, was slowly moving from the core towards the mantle. That movement also generated a circulation in the liquid core that would eventually create Earth’s primitive magnetic field. By the time the “fuel,” magnesium oxide, ran out (probably from the extreme heat related to the giant impact that formed Earth’s moon), the magnetic field nearly collapsed, scientists believe. But since the solid inner core formed around the same time, it came at the perfect time to save life on Earth. Just in time, as the formation of the inner core provided a new energy source to power the geodynamic and planetary magnetic shield that the Earth possesses today.
Thus, this study will help scientists to draw conclusions about the sustainability of the Earth’s magnetic shield and whether there are other planets within the solar system with the ideal conditions to host life.
Referencia: John A. Tarduno el al., “Paleomagnetism indicates that primary magnetite in zircon records a strong Hadean geodynamo,” PNAS (2020). www.pnas.org/cgi/doi/10.1073/pnas.1916553117
