Question

how does the ocean floor keep track of magnetic fields?
being underwater makes the rocks respond to magnetic fields.
there are magnets in the ocean floor.
basalt is iron - rich and responds to magnetic fields.
all rocks act like magnets.

Explanation:

Basalt is an igneous rock that contains iron - rich minerals. As new ocean floor forms at mid - ocean ridges (due to volcanic activity), the basalt cools. As it cools, the iron - rich minerals in basalt align with the Earth's magnetic field at that time. This records the direction of the magnetic field. When the Earth's magnetic field reverses (a known geological phenomenon), the next layer of basalt (as it forms and cools) will record the new magnetic field direction.

• Option 1: Just being underwater does not make rocks respond to magnetic fields. Many non - magnetic rocks can be underwater.
• Option 2: There are no large - scale "magnets" in the ocean floor in the sense of permanent magnets like bar magnets.
• Option 4: Not all rocks act like magnets. For example, sedimentary rocks like limestone (which is mainly calcium carbonate) do not have the magnetic - recording properties of basalt.

Answer:

Basalt is iron - rich and responds to magnetic fields.