Geology of the Pacific Ocean . The Pacific Ocean developed from the Panthalassa, a vast global ocean, following the breakup of the supercontinent Pangaea in the Mesozoic Era, gradually forming Gondwana and Laurasia, which in turn divided. There is no firm date for when the changeover occurred, as the replacement of the sea bed is a continuous process, though reconstruction maps often change the name from Panthalassic to Pacific around the time the Atlantic Ocean began to open. The Panthalassic Ocean first opened around 750 million years ago at the breakup of Rodinia, but the oldest Pacific Ocean floor is only around 180 Ma old.
Gondwana Late Triassic and became important in the Jurassic and Cretaceous. It is possible that gymnosperm biodiversity surpassed later angiosperm biodiversity and that the evolution of angiosperms began during the Triassic but, if so, in Laurasia rather than in Gondwana. Two Gondwanan classes, lycophytes and sphenophytes, saw a gradual decline during the Triassic while ferns, though never dominant, managed to diversify. The brief period of ice house conditions during the Triassic–Jurassic extinction event had a dramatic impact on dinosaurs but left plants largely unaffected. The Jurassic was mostly one of hot house conditions and, while vertebrates managed to diversify in this