For much of its geologic history, South America was part of a supercontinent comprised of many southern hemispheric land masses. South America began to split apart from Africa 130 million years ago and separated from Antarctica within the past 50 million years. At 6.88 million square miles, it is the fourth largest continent on Earth. South America is dominated by two major landforms. The Andes Mountains, located within the Pacific Ring of Fire, are formed from the subduction of the Nazca plate underneath the entire western edge of the South American plate. Like all other areas within the Ring of Fire, South America is prone to volcanic activity and strong earthquakes. The eastern half of the continent is underlain by several cratons, all over one billion years in age. In between the cratons and Andes are sediment-covered lowlands. The continent is barely connected to North America through the Isthmus of Panama and is almost completely surrounded by the Pacific, Atlantic and Carribean Oceans. Almost all of South America’s great river systems, including the Amazon and Orinoco, begin in the highlands and drain east towards the Atlantic or Caribbean Oceans. Argentina’s geology is dominated by the metamorphic and igneous rocks of the Andes to the west and a large sedimentary basin to the east. A small, northeastern section of the country extends into the Río de la Plata craton. To the south, the Patagonia region stretches between the Pacific and Atlantic Oceans and contains some of the largest non-polar glaciers in the world. It should be noted that Argentina contains some of the world’s richest fossil sites that are home to both gigantic dinosaurs and famous paleontologists.