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New Theory on the Earth’s Crust
Vicki Hansen, McKnight Presidential Professor of Earth and Planetary Sciences, in UMD's Department of Geological Sciences, has contributed a hypothesis regarding the initiation of plate tectonics that made international news.
Hansen proposes that the formation and recycling of Earth’s ocean crust (that is, plate tectonics), may have started with the massive impact of a bolide (asteroid or comet) during Earth’s infancy.
Geologists estimate that sometime around 4 to 2.5 billion years ago rocky plates began to slide across Earth’s surface. Before that time Earth’s crust may have been too warm to act like plates. Once formed, plates collided to build mountain ranges, and spread to form new ocean crust. Oceanic crust was recycled back to the Earth’s mantle through ‘subduction’, diving beneath less dense crust, and serving to moderate Earth’s atmospheric gases, and therefore its surface temperature for billions of years. Geologist enthusiastically debate when and how plate tectonics began.
Hansen’s simple hypothesis, or thought experiment, challenges geologists to consider the Earth and its early evolution within the context of Earth’s formative environment — a young solar system with many bolides. Hansen said, "Understanding our incredible planet may require us to look beyond Earth’s present boundaries and to consider events that while rare today, were common 3-4 billion years ago."
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