What ocean-floor evidence showed that Earth's magnetic field reversals are mirrored on both sides of mid-ocean ridges?

• A. Fossil distribution across continents
• B. Mirror-image magnetic stripes on either side of mid-ocean ridges
• C. Seafloor age increases away from ridges
• D. Volcanic activity is constant along ridges

Answer: (B)

Magnetic reversals leave a visible record in the ocean floor. As new magma erupts at a mid-ocean ridge and cools, the iron minerals align with Earth’s current magnetic field. When the field reverses, the newly formed rock records the opposite polarity. Over time, this creates alternating bands of normal and reversed magnetization on either side of the ridge. Because the crust spreads outward in both directions, the stripes are mirror images on opposite sides, providing strong evidence that reversals happen globally and that seafloor spreading moves rocks apart from the ridge. The other options don’t capture this mirrored magnetic pattern: fossil distributions relate to continental drift, not magnetic reversals; seafloor age away from ridges shows spreading but not polarity reversals; and constant volcanic activity along ridges isn’t about magnetic records.