1. How was the recognition that the polarity of the earth\'s magnetic field reve

Question

1. How was the recognition that the polarity of the earth's magnetic field reversed episodically a significant observation and contribution in the evolution of the theory of plate tectonics? (i.e., How was this recognition critical to the recognition by Vine & Matthews that the marine magnetic anomalies they mapped across the mid-ocean ridge south of Iceland demonstrated that the Sea Floor Spreading theory of Harry Hess was indeed valid?)

2. What is magnetic inclination of the earth’s magnetic field, and how is it related to the latitude that you are at on the earth’s surface? (i.e., What is it at the equator, pole, and somewhere in between, that indicates latitude?)

Explanation / Answer

1)Henry Hess proposed the sea floor spreading hypothesis in 1960.According to his theory sea floor was created at mid - oceanic ridges by the convection of the Earth's mantle by pushing and spreading the old crust away from the ridge.

Vine and Mathew realized that Hess 's sea floor spreading theory was correct .So they did investigation on the hypothesis.They thought that if Hess's sea floor spreading theory was correct, then the rocks surrounding the mid oceanic ridges should show magnetic reversals.Vine and Mathew 's hypothesis describes the magnetic reversals of oceanic crust.At the mid oceanic ridge a new crust is created by injection ,solidification ofmagma.After the magma has cooled then the magnetic minerals in the newly formed crust orient themselves with the geomagnetic field .This new crust pushes the old crust either side of the ridge .Hence geomagnetic reversal occurs. Thus it has significant contribution on the evolution of the theory of the plate tectonics.

2)Magnetic dip or magnetic inclination is the angle made by the needle of a vertical compass.Magnetic dip is the angle made with the horizontal by the Earth's magnetic field lines.This dip or the angle may different at different points on the surface of the Earth.Positve values of inclination shows that the magnetic field of the Earth is facing downward .If it shows negative values then it points upward.

Magnetic dip align with lines of force of Earth.As the Earth's magnetic lines of force are not parallel to the surface, the north end of a compass needle will point upward in the southern hemisphere and shown as negative dip.It will point downward in the northern hemisphere called positive dip.

At equator the dip will be Zero dip.

At the North pole it is positive 90 degrees.

At the south pole it is negative 90 degrees.

At the other latitudes small amount of dip will be evident in latitudes less than 60 degrees north and south.

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