About 300 million years ago, Earth didn't have seven continents, but instead one massive supercontinent called Pangaea, which was surrounded by a single ocean called Panthalassa.
One of the key pieces of evidence for Pangaea (sometimes spelled Pangea) emerges from the fossil record, where identical species, such as the seed fern Glossopteris, are found on now widely disparate continents. The orientation of magnetic minerals in geologic sediments reveals how Earth's magnetic poles migrated over geologic time. And mountain chains that now lie on different continents, such as the Appalachians in the United States and the Atlas Mountains in Morocco, were all part of the Central Pangaea Mountains, formed through the collision of the supercontinents Gondwana and Laurussia.
Formation and breakup
Throughout Earth's 3.5 billion-year history, supercontinents have formed several times. Pangaea formed through a gradual process spanning a few hundred million years. Beginning about 480 million years ago a continent called Laurentia, which includes parts of North America, merged with several other micro-continents to form Euramerica. Euramerica eventually collided with Gondwana, another supercontinent that included Africa, Australia, South America and the Indian subcontinent.
Plant and animal life
Pangaea existed for 100 million years, and during that time period several animals flourished, including the Traversodontidae, a class of plant-eating animals that was part of the class that includes the ancestors of mammals.
During the Permian period, insects such as beetles and dragonflies and flies flourished.
But the existence of Pangaea overlapped with the worst mass extinction in history, the K-T extinction. The Great Dying occurred around 250 million years ago and caused most species on Earth to go extinct. It took about 10 million years for species diversity to recover.
The early Triassic period saw the rise of archosaurs, a group of animals that eventually gave rise to crocodiles and birds, and a plethora of reptiles. And about 230 million years ago some of the earliest dinosaurs emerged on Pangaea, including theropods, largely carnivorous dinosaurs that mostly had air-filled bones and feathers similar to birds.
But around 200 million years ago, the supercontinent began to break up, forming the two continents Gondwana and Laurasia. Then about 150 million years ago, Gondwana further split into four continents and India. And around 60 million years ago, North America split off from Eurasia.
Cycle in history
The current configuration of continents is unlikely to be the last. Supercontinents have formed several times in Earth's history, only to be split off into new continents in a continuous process. Right now, for instance Australia is inching towards Asia and the eastern portion of Africa is slowly peeling off from the rest of the continent.