Complex sentence: A giant intrusion of magma happened in the Jurassic forming diabase, or dolerite which gives many of the Tasmanian mountains their characteristic apptal breakup happened in the Cretaceous and Tertiary Periods, splitting off undersea plateaus, forming Bass Strait and ultimately breaking Tasmania away from Antarctica.
Split into simpler sentences: A giant intrusion of magma happened in the Jurassic forming diabase, or dolerite which gives many of the Tasmanian mountains their characteristic appearance. Continental breakup happened in the Cretaceous and Tertiary Periods, splitting off undersea plateaus, forming Bass Strait and ultimately breaking Tasmania away from Antarctica.