Oceanic crust is continuously created at mid-ocean ridges and destroyed by subduction at convergent margins, giving it a much shorter lifespan than continental crust. As a result, no oceanic crust older than about 200 million years (Jurassic) survives on Earth today.
Symmetric magnetic anomaly stripes on either side of a mid-ocean ridge (like the Mid-Atlantic Ridge) form as newly created oceanic crust records the polarity of...
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