Probing the Age of the Oldest Ocean Crust in the Pacific

The geomagnetic polarity time scale (GPTS) is based on the marine magnetic anomalies, the striping pattern of strong and weak magnetic signals recorded by the ocean crust. Strong signals correspond to normal polarity and weak signals to reverse polarity. Adjacent normal and reverse stripes are numbered, backward in time from C1 (top = today) to C34, of which the normal portion is a long period of normal polarity in the Mid Cretaceous. Older magnetic stripes are referred to as the M-sequence (Mesozoic sequence) starting with M0 below the very long C34 anomaly.

The current GPTS extends from today backward in time down to magnetic anomaly M29 (approximately 157 million years ago). Older oceanic crust is…

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