Red dot shows location of Chicago.
Plate tectonics is the theory that the Earth’s crust is composed of rigid plates that float on the Earth’s pliable mantle. There are two types of plates: thick, light continental plates composed mostly of granite (aluminum silicates) and thin dense oceanic plates composed mostly of basalt (magnesium and iron silicates). Convection currents caused by the heat of radioactive elements decaying in the Earth’s mantle and core cause the plates to move. When two plates collide there are 4 possible boundaries. At a continental-continental boundary large mountains are uplift example the Himalayas. At a continental-oceanic plate the heavier oceanic plate slides underneath the lighter continental plate melts and the lighter material floats back up forming volcano chains like the Cascades and Andes. At an oceanic-oceanic plate boundary one plate slides below another and a volcanic island arc forms like Japan. Sometimes plates just slide by each other as in a transform boundary. This type of boundary causes many earthquakes; the San Andreas Fault is an example of a transform boundary. Understanding plate tectonics is important for studying Silurian reefs because it explains how plates and continents move over the surface of the planet. As the landmasses move they can go from tropical to temperate to polar regions and the fossils preserved in the rocks deposited at this time record these changes allowing us to examine and explore ancient environments and how they are related to the past position of ancient landmasses.