Anatomy of Mid-Ocean Ridges

 Mid Oceanic Ridge Below Africa

As we learned in chapters 18 and 19 the mid oceanic ridge is driven by convection. The hot mantle rock rising from below forces spreading and creates new rock on the ocean floor. This is why paleomagnetism is possible. The new rock formed from new basalt eruptions in the ridge valley and on the ridge crest gives actual magnetic time stamps of the formation of the ocean floor and also reveals how magnetism has changed over that time; at least 200 million years, right? The ocean floor is relatively young in comparison to the ocean water, created 4 billion years ago.

Arizona 300 Million Years Ago

Parts of the United States was once under sea water during different times in Earth's history. This website gives interesting insight into phases  North American has been through historically. In what this site defines as the "coal age", during the Pennsylvanian Period, Arizona was under sea water.