1.3 Magnetic striping

Question 1

Magnetic Striping

Answer 1

• Earth has a geographic North and a geographic South as well as a magnetic North and magnetic South.
• The geographic North and geographic South do not change.
• However, the magnetic North and magnetic South can shift, and they have reversed multiple times over geological time.
• Currently, the magnetic North points roughly towards the geographic North and the magnetic South points roughly towards the geographic South - this is known as normal polarity.
• Reverse polarity happens when the magnetic North points roughly towards the geographic South, and the magnetic South points roughly towards the geographic North.
• Over geological time, the Earth’s polarity has flipped multiple times, alternating between normal and reverse polarity

Question 2

Evidence from rock patterns

Answer 2

• rocks created along the spreading oceanic ridges preserve pattern of polarity reversal as they cool
• pattern can be used to determine the rate of ocean ridge
• alternating polarity forms a striped patterns
• with each reversal of the earth’s polarity, magnetic minerals in the rocks align themselves with the magnetic North and South, forming a striped pattern
• when poles reverse, Earth’s magnetic north and south poles swap locations
• this zebra-like pattern is symmetrical on either side of mid-ocean ridges, showing that this is not a random or isolated occurrence

Question 3

Why magnetic striping occurs

Answer 3

• Basaltic rocks from the oceanic crust are volcanic rocks formed from iron-rich lava.
• They contain magnetic materials.
• When the iron-rich lava erupts, it cools and solidifies.
• Its magnetic materials point towards Earth’s magnetic North, recording evidence of Earth’s polarity at that time.

Question 4

How it works

Answer 4

1. Oceanic plate move away from each other
2. Iron-rich lava erupts, cools, solidifies, forms new oceanic crust at crest of ridge
3. Crust is pushed in both directions away from the ridge when new lava is solidifies as plates moves apart
4. Earth’s polarity will reverse, rocks records reversals
5. as more lava moves away from the ridge due to plate divergence, a symmetrical zebra-like pattern forms