There are few terranes that illustrate the science of plate tectonics and continental drift better than Avalonia. This micro-continent formed as a volcanic island arc along a subduction zone off the African Coast; at that time, late in the Precambrian Era, Africa was attached to the other southern continents to form Gondwana, which stretched across the South Pole. During the Cambrian Period, some 530 million years ago (MYA), as shelled marine life was exploding in diversity, Avalonia rifted from the African Plate and drifted northward ahead of the Rheic Ocean, which opened between it and Gondwana.
Late in the Ordovician Period, some 450 MYA, Avalonia docked with Baltica, the craton that now underlies Scandinavia, Eastern Europe and western Russia. This combined continental mass then collided with Laurentia (proto-North America) during the Silurian Period (440 MYA) as plants and animals were first colonizing the land; the collision forced up the Northern Appalachians, an event known as the Acadian Orogeny. When the Earth's land masses merged into Pangea during the Permian Period, about 270 MYA, Avalonia was caught in the middle, compressed between the northern and southern continents.
As the Tethys Sea opened east to west, some 200 MYA, Avalonia remained with Laurasia (the combined northern continents). During the Jurassic (150 MYA), the Atlantic Ocean began to open, splitting Avalonia as it divided the North American and Eurasian Plates. Today, fragments of Avalonia form coastal New England, Nova Scotia and the Avalon Peninsula of Newfoundland on the North American Continent; across the Atlantic, it is represented by Wales, England and the northern portion of Western Europe. Small fragments of Avalonia have also been identified in South Carolina and along the western rim of the Iberian Peninsula.