Suppose a geologist is studying two distinct
areas next to a spreading ridge. The magnetic
direction of the minerals in the oldest area is
opposite to the magnetic direction of minerals
in the newest area.
(a) Which area is closest to the centre of the
ridge, the older or newer area? Explain.
(b) What can the geologist conclude about
Earth’s magnetic field during the time
when the two areas formed?
gio
Pangaae
To determine which area is closest to the center of the ridge and explain the magnetic directions, we need to understand the process of seafloor spreading and Earth's magnetic field.
(a) The geologist can determine which area is closest to the center of the ridge by considering the process of seafloor spreading.
Seafloor spreading occurs at mid-ocean ridges, where tectonic plates move apart, and new oceanic crust is formed. As the plates move apart, magma rises from the mantle and solidifies, creating new seafloor. The solidified rocks on the ocean floor preserve the record of Earth's magnetic field at the time of their formation.
The magnetic minerals in the oceanic crust align themselves with the Earth's magnetic field as they solidify. However, Earth's magnetic field has undergone reversals throughout its history, where the North and South magnetic poles have switched places. These magnetic reversals leave a distinct pattern in the rock layers along the spreading ridge.
In this scenario, if the magnetic direction of the minerals in the oldest area is opposite to the magnetic direction of minerals in the newest area, it suggests that there has been a magnetic reversal between the time the two areas formed. The newer area with the reversed magnetic direction is closer to the center of the ridge because it formed more recently when the reversing magnetic field was in effect.
So, the newer area is closest to the center of the ridge.
(b) Based on the opposite magnetic directions in the two areas, the geologist can conclude that Earth's magnetic field has undergone a reversal during the time when the two areas formed. This means that the North and South magnetic poles switched places at some point.
The preservation of these magnetic directions in the rocks provides evidence for the historical changes in Earth's magnetic field. By studying the magnetic patterns recorded in the oceanic crust, geologists can reconstruct the sequence of magnetic reversals that have occurred throughout Earth's history. This information is crucial for understanding the process of seafloor spreading and plate tectonics.