Question

Earth’s magnetic field has reversed itself several

times during the past. This pattern of magnetic
reversal is best preserved in
(1) metamorphic bedrock in mountain ranges
(2) bedrock with fossils containing radioactive
carbon-14
(3) layers of sedimentary bedrock of the Grand
Canyon
(4) igneous bedrock of the oceanic crust

Answer 1

Earths magnetic reversals are best recorded in the igneous bedrock of the oceanic crust, where solidifying molten material from the mid-Atlantic ridge captures the magnetic orientation at the time of cooling.

Step-by-step explanation:

The pattern of magnetic reversal is best preserved in igneous bedrock of the oceanic crust, specifically option (4) from the question. Volcanic activity at the mid-Atlantic ridge causes new material, which includes igneous rock, to extrude and fill the gap between separating tectonic plates. As this molten rock solidifies, it records the Earth's magnetic field at that time. The sediment then cools and becomes part of the ocean floor, effectively crystallizing a snapshot of the magnetic field. Repeated over time, we see a pattern of magnetic stripes on either side of the ridge that serve as a record of the planet's history of magnetic reversals. Moreover, by measuring the rate at which the sea floor spreads, scientists can estimate the age of these stripes and construct a Geomagnetic Polarity Time Scale (GPTS).

Answer 2

The best answer is option 4.

On Earth, the record of the reversal of the magnetic field is preserved in magnetic rocks which lie along the ocean floor. The magnetism preserved in these rocks point first in one direction then in another direction, giving the ocean floor a stripped appearance (from a magnetic point of view)

Earth's magnetic field is powered by the core of the planet. At its center, is a solid inner core surrounded by a fluid outer core that is hotter at the bottom. Hot iron rises within the outer core then cools and sinks. The convention currents combined with the rotation of the earth are thought to generate a geodynamo that powers the magnetic field.