The maps and globes that adorn our walls, shelves, and books give an impression of a static Earth. It would be easy for us to assume that the continents have always been where they are. But we would be wrong. Earth's crust consists of a number of solid plates approximately 40 km thick, which float on a fluid mantle. The mantle fluid circulates because heat produced by radioactive decay sets up convection patterns in the fluid. The plates move because material from the mantle rises and pushes them aside. Where plates are pushed together, either they move sideways past each other, or one plate moves under the other, pushing up mountain ranges. The movement of the plates and the continents they contain is known as continental drift.
At times, the drifting of the plates brought the continents together; at other times, they drifted apart. The positions and sizes of the continents influence ocean circulation patterns, sea levels, and global climate patterns. Mass extinctions of species, particularly marine organisms, have usually accompanied major drops in sea level, which exposed vast areas of the continental shelves, killing the marine organisms that lived in the shallow seas that had covered them (Figure 22.2).
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.