Plate tectonics (Part 2): A closer look

Helen Gould (UK) As we saw last time (Plate tectonics (Part 1): What are they?), the Earth is a pretty dynamic place, with tectonic plates moving about on the surface, driven by convection cells in the upper mantle. But producing a workable theory, which combined most of the observations of geological evidence, took years. It was known that the centres of continents were extremely old, and that some areas around the continental “cratons” didn’t seem to belong because they contained completely different types of rocks. Combining continental drift with seafloor spreading and mantle convection currents produced the idea of plate tectonics, and provided an explanation for the odd rocks on areas fringing some cratons. These “microplates” had come from other areas of the Earth, where different geological processes had produced different rock types. The role of density in recycling: oceanic and continental crust The physical features of the ocean basins and continental mountain ranges are known as the “crustal dichotomy” (splitting of the crust into two equal parts), and because these types of feature are essentially dissimilar, they have their own rock types. Basalt is the commonest rock both in the Solar System and on Earth, where it forms the ocean floor, along with various sedimentary rocks deposited underwater which make up another 5% of the total oceanic crust. Continents typically consist of coarse-grained rocks related to granites, which solidify below ground. Comparing similar-sized pieces of basalt and granite in the hand will establish obvious physical differences between them. Basalt’s … Read More

To access this post, you must purchase Annual subscription, 12 Month Subscription or Monthly subscription.
%d bloggers like this: