You haven't included answer choices, so my answer may not match up with the answers you have to choose from. However, this has to do with the polar reversal theory, which was developed after the discovery of magnetic striations at the bottom of the Marianas Trench. According to this theory, Earth's magnetic poles reverse every 200,000-350,000 years due to the constant recycling of Earth's crust through subduction of tectonic plates.
