Radiometrically dating adjacent rocks
In the early 1960s new data from ocean exploration led to the idea of seafloor spreading.A few years later, these and other concepts were synthesized into the model of plate tectonics, which was originally called "the new global tectonics." According to the orthodox model of plate tectonics, the earth's outer shell, or lithosphere, is divided into a number of large, rigid plates that move over a soft layer of the mantle known as the asthenosphere, and interact at their boundaries, where they converge, diverge, or slide past one another. -- This paper looks at the challenges confronting plate tectonics -- the ruling paradigm in the earth sciences.
How do we know this and how do we know the ages of other events in Earth history?Principles of Stratigraphy Stratigraphy is the study of strata (sedimentary layers) in the Earth's crust.Geologist in the 1800s worked out 7 basic principles of stratigraphy that allowed them, and now us, to work out the relative ages of rocks.It met with widespread rejection, largely because the mechanism he suggested was inadequate -- the continents supposedly plowed slowly through the denser oceanic crust under the influence of gravitational and rotational forces.Interest was revived in the early 1950s with the rise of the new science of paleomagnetism, which seemed to provide strong support for continental drift.