Conceptual illustration of the Permian environment of the Sydney Basin, Australia, 250 million years ago. At this time extensive seasonally cool climate leads to ice rifting throughout the intertidal zones depositing dropstones. Later as water levels decreased Glossopteris and Glossopteridales, an extinct order of plants belonging to Pteridospermatophyta, or seed ferns, covered much of the area forming thick peat that was eventually to become coal that formed the Bulli Coal Measures before Permian Triassic extinction event.