Why is Earth a Magnet? (Part Two)



We’ve been wondering for a while if the hot spots, which are found around the Earth’s crust, are weak points in the earth’s magnetic fields (or strong points?) The earth’s magnetic field is changing rapidly and as it’s also induced by the sun’s magnetic field, which is also in a weak period, perhaps we will see an apparent increase in volcanic activity or the awakening of long dormant volcanic fields, such as the Garrotxa volcanic field in Spain or the Chaine du Puys in France? What seems amazing this year is the volcanic and seismic activity, in Italy, Tonga, Chile, Alaska, the Caribbean, Hawaii to name some areas.


What causes a Volcano, or an earthquake? Giant plates in the earth’s crust.

The overall pattern of movement of the tectonic plates is a widening of the Atlantic Ocean and a shrinkage of the Pacific Ocean. The Atlantic is widening because sea-floor spreading at the Mid-Atlantic Ridge continues to create lithosphere. The Pacific is shrinking because much of it is ringed by convergent plate boundaries that are consuming its lithosphere.

Scientists have traced the movements of tectonic plates millions of years into the past. According to the commonly accepted description of plate movement, all the continents once formed part of an enormous single land mass called Pangaea. A giant ocean known as Panthalassa surrounded this mass.

About 200 million years ago, Pangaea began to break up into two large masses called Gondwanaland and Laurasia. These masses, in turn, broke up into the continents, which drifted to their present locations.


Earth scientists find much evidence of plate movement at the boundaries of plates. They study surface features, such as mountains and ocean trenches, and investigate the frequencies and locations of earthquakes and volcanic eruptions.

Volcanoes that rise within plates are also evidence of plate movement. Scientists believe that these volcanoes are caused by mantle plumes, columns of very hot mantle that rise from deep inside Earth to the base of the lithosphere. These plumes generate magma that rises through the lithosphere and erupts in places called hot spots.

As a plate moves over a hot spot, the spot can generate a chain of volcanoes. For example, a hot spot under the Pacific Plate generated volcanoes that became the Hawaiian islands.

Paleomagnetism (the study of magnetism in ancient rocks) also provides evidence of plate movement. The evidence is in rocks that contain magnetic particles.

When such a rock was hot and liquid, the magnetic particles moved too rapidly to be influenced by Earth’s magnetic field. But as the rock cooled and solidified, the particles aligned themselves with Earth’s magnetic field, like tiny compass needles. Then, the particles continue to point in the direction of the magnetic field that was present during the time that the rock cooled.

So when the plate containing the rock either drifts to a different latitude or rotates, the particles no longer align with Earth’s magnetic field. A comparison of the direction in which the particles now point in the rock with the direction of Earth’s present magnetic field provides information about where the plate was when the rock solidified.


Tectonic plates slide mostly because of temperature changes and gravity. As an edge that has formed on the ocean floor cools, it shrinks, becoming denser. After about 25 million years of cooling and shrinking, the edge becomes so dense that gravity can pull it down into the asthenosphere. Because of the additional density, gravity pulls the plate edge into the asthenosphere even more strongly.

Gravity also causes plates to slide downhill away from ocean ridges. This sliding force is called ridge-push.

The circulation of mantle rock as it rises to the top of the asthenosphere, cools, and then sinks it is known as convection current.

A new technique for measuring the Earth’s magnetic field back to the days of the dinosaurs and beyond has revealed that the field was as much as three times stronger in ancient Earth than previous techniques suggested.

Scientists use the record of the Earth’s magnetic field locked in rocks to tease out secrets of the geodynamo – the currents of molten rock that seethe beneath the Earth’s crust, causing everything from earthquakes and volcanoes to the drift of the continents themselves.

Researchers have known that the magnetic poles have flipped several times during our planet’s lifetime –  meaning a compass 100,000 years ago could have pointed south instead of north. Great bands of rock displaying north-south flips are laid across the ocean floors.

With the method tested, it was time to see what it revealed about the magnetic field back in the days of the dinosaurs. It took dozens of samples from lava flows in India that were nearly 100 million years old. Besides possibly giving T-Rex a better northern lights show, the field strength gives researchers a glimpse into what the Earth’s hot, molten core was doing back then.


After molten lava emerges from a volcano, it solidifies to a rock. Its magnetization is in the direction of the local magnetic force at the time when it cools down.

The polar field of the Sun seems to reverse every 11 years or so, taking about a year or more. But the Sun’s magnetism is different; it has foci right on the surface, in sunspots.

Is the Earth’s field getting weaker? Yes and no. If the Earths magnetic field weakens, will volcanism and plate tectonics increase?

Compare two maps, and note the ring of fire and the magnetic map.


Scientists at the University of Liverpool have discovered that variations in the long-term reversal rate of the Earth’s magnetic field may be caused by changes in heat flow from the Earth’s core. The scientists focused on the time interval between around 200 and 80 million years ago, when magnetic polarity started reversing very frequently – up to 10 times every million years. However 50 million years later, it stopped reversing altogether for nearly 40 million years. “We suspect that this process … changed the pattern of heat flowing out of the core in such a manner as to cause the magnetic field to first become less stable, with lots of reversals, and then become much more stable – and stop reversing,” said “Dr. Andrew Biggin”, from the University’s School of Environmental Sciences.  According to Nature.com, large igneous provinces (LIPs) are known for their rapid production of enormous volumes of magma (up to several million cubic kilometers in less than a million years), for marked thinning of the lithosphere, often ending with a continental break-up, and for their links to global environmental catastrophes.

The Siberian Traps and Deccan Traps, where huge amounts of magma poured out of the earth, were both synchronous with large mass-extinction events – the Great Permian extinction and the dinosaur extinction.


It is now possible to bring together recent, previously unknown, and amazing correlations
that have been shown to exist between different parts of the solar wind -
magnetosphere – ionosphere – solid Earth system, in particular with respect to earthquake
 activity. There is strong evidence of electromagnetic processes responsible for
earthquake triggering.The connection of earthquake activity
to possible solar or solar wind drivers is not well understood. The ionosphere modulates
waves transmitted to the ground so we only compare the wave power and not the
waves themselves for the ground-based magnetometers.

“If we were typical, we should not exist …
we humans should be the descendants of long-ago settlers from somewhere else.” von Hoerner 1978

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