Pangaea was a super-continent – an agglomeration of multiple continents – that came into being about 250 million years ago. It was composed of all the continents we know today fused into a single landmass, surrounded by a single ocean (called Panthalassa) – and was the last time such a thing occurred. In fact, it was slightly larger than the combined areas of the modern continents, as supercontinent formation tends to lead to lower sea levels.
Pangaea (the name comes from the Greek Pan meaning All and Gaea meaning Earth) existed during the Paleozoic and Mesozoic eras, and its best known inhabitants were the dinosaurs. It began to break up approximately 75 million years after it formed, although the continents would not reach anything approximating their modern positions until only about 35 million years ago, when the Indian subcontinent collided with Asia.
As mentioned in:
The Big Bang Theory — Barenaked Ladies