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But the stripes that Bridges' team found in Tendaho may prove that conventional wisdom wrong.
Tendaho's magnetic bands, which measure 6 miles (10 kilometers) wide, are embedded in continental crust, not oceanic crust. And unlike magnetic stripes on the ocean floor, Tendaho's formed through diking: as the African crust stretched thin, streams of magma intruded the continental crust and hardened. Like in the oceanic stripes, ferromagnetic minerals in the dikes aligned with the planet's magnetic field as the magma hardened. Their magnetic signals are very similar to those of ocean-floor stripes.
This all happened sometime between 1.8 million years ago, when the region's continental crust began to break apart, and 780,000 years ago, when the Earth's magnetic poles last flipped, Bridges said.
Scientists predict it could be as many as 2 million years before the crust in the Tendaho Graben ruptures and
begins to form an ocean basin. Altogether, this means that Tendaho's magnetic stripes could predate the future ocean basin by nearly 4 million years.
