The Earth's magnetic field is a geomagnetic field powered by convection currents of molten iron and nickel in our planet's core. It shields the Earth from cosmic radiation, like solar winds, and from the charged particles released by the Sun. Additionally, it provides useful information for orientation and navigation by serving as the basis for a magnetic compass.
In a recent discovery, scientists have found evidence that the magnetic field already existed very early in Earth's history.
Understanding Earth's Magnetic Field
The presence of a magnetic field is vital for the formation of life on Earth. Experts strongly believe that the existence of an ancient magnetic field could have helped life get a foothold on our planet.
In previous studies, it was assumed that estimates and hints of Earth's early magnetic field have originated from mineral crystals known as zircons found within ancient rocks from Western Australia. These crystals suggested that the magnetic field existed about 4.2 billion years ago. However, this claim was doubted as unreliable.
Today, the magnetic field is generated by the dynamo effect by electrical currents in the molten iron outer core of our planet. This effect is triggered by the buoyancy forces as Earth's inner core cools and solidifies.
A Piece of Earth's History
Geologists have found ancient rocks in Greenland which show an ironclad record of our planet's magnetic field. These rocks are dated back to 3.7 billion years ago, making them the oldest record of the Earth's ancient magnetism. However, this discovery is quite mysterious.
It is hard to find rocks that are almost 4 billion years old. Most of them have been recycled through the Earth's tectonic activity by sliding down into the mantle through subduction zones before being thrown out by volcanoes. Still, a sequence of rocks in the Isua Supracrustal Belt in Greenland managed to survive the ravages of time. Scientists believed that it was due to its unique geology, since it is located on top of a thick continental plate that acts like a life-raft in the middle of an ocean.
Just recently, scientists from the Massachusetts Institute of Technology (MIT) and the University of Oxford decided to dig up some of the Isua rocks. They found that the Earth's magnetic field does not seem to have changed very much at all throughout its history. Still, experts are not sure where that magnetic field could have come from.
Unlike the previous claims from zircon crystals, the results from Isua rocks are considered more reliable. For the first time, they are based on entire iron-bearing rocks to derive the prehistoric field strength. This means that the sample provides the first solid measure of the strength of Earth's early magnetic field and also the timing of when it originally appeared.
The iron particles within the Greenland rocks act like tiny magnets which align with Earth's magnetic field when the rock around them crystallized for the first time 3.7 billion years ago. This alignment holds a record of the strength of Earth's early magnetic field, measured to have been at least 15 microtesla which is comparable to the current field strength of 30 microtesla.
RELATED ARTICLE : Iron Atoms Found Moving Inside the Earth's Solid Inner Core, Affecting the Magnetic Field With Their Collective Motion
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