<P> There were three major phases in the break - up of Pangaea . The first phase began in the Early - Middle Jurassic ( about 175 Ma ) , when Pangaea began to rift from the Tethys Ocean in the east to the Pacific in the west . The rifting that took place between North America and Africa produced multiple failed rifts . One rift resulted in a new ocean , the North Atlantic Ocean . </P>
what land mass was north america a part of about 300 million years ago
Pangaea