Question

which evidence best supports the pattern of earth’s magnetic field changing from normal to reversed?
spreading ridge
4 million years ago
2 million years ago
present day
normal magnetic polarity
reversed magnetic polarity
oceanic crust on both sides of the ridge is less dense than continental crust.
large sedimentary folds exist in the mantle near the ridge.
the iron elements in the oceanic crust reveal symmetrical patterns that point north and south.
oceanic crust is oldest at the mid - ocean ridges

Explanation:

To determine which evidence supports Earth’s magnetic field changing from normal to reversed, we analyze each option:

• Option 1: Oceanic crust density vs. continental crust is about crustal density, not magnetic field changes.
• Option 2: Large sedimentary folds in the mantle relate to sedimentary structures, not magnetic field reversals.
• Option 3: Iron elements in oceanic crust show symmetrical magnetic polarity patterns (normal/reversed) on either side of mid - ocean ridges. This symmetry matches the pattern of magnetic field reversals over time, as new crust forms at ridges and records the magnetic polarity of the era.
• Option 4: Oceanic crust age at mid - ocean ridges is about crustal age (youngest at ridges), not magnetic field reversals.

Answer:

The iron elements in the oceanic crust reveal symmetrical patterns that point north and south.