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 Ice House to Hot House. By the end of the Ordovician "Cooksonia", a slender, ground-covering plant, became the first vascular plant to establish itself on land. This first colonisation occurred exclusively around the Equator on landmasses then limited to Laurasia and, in Gondwana, to Australia. In the Late Silurian two distinctive linages, zosterophylls and rhyniophytes, had colonised the tropics. The former evolved into the lycopods, that were to dominate the Gondwanan vegetation over a long period, whilst the latter evolved into horsetails and gymnosperms. Most of Gondwana was located far from the Equator during this period and remained a lifeless