Daily Postcard: Two scientific bore holes from a paleomagnetism study on Cerro Abrigo. I heard that Valles Caldera helped prove the theory of plate tectonics. How so? When scientists were working to verify the theory of plate tectonics in the 1960s, Valles Caldera was an ideal study location due to the occurrence of certain aged volcanic rocks. Similarly aged rocks from Valles Caldera’s lava domes and from the ocean floor were analyzed for their symmetrical stripes of alternating normal and reversed magnetic polarity. Some of the young reversals of the Earth’s magnetic field that were found on the sea floor were also discovered in rocks at three domes in northern Valles Caldera: Cerro Abrigo (normal polarity), Santa Rosa (transitional polarity), and San Luis (reverse polarity). Valles Caldera provided confirmation of some fundamental plate tectonics concepts, especially sea floor spreading, leading to widespread acceptance of the theory that has unified the science of geology. Courtesy/Don Usner