 The reef's substrate may have needed to build up from the sediment until its edge was too far away for suspended sediments to inhibit coral growth.In addition, approximately 400,000 years ago there was a particularly warm Interglacial period with higher sea levels and a water temperature change.The land that formed the substrate of the current Great Barrier Reef was a coastal plain formed from the eroded sediments of the Great Dividing Range with some larger hills (most of which were themselves remnants of older reefs or, in rare cases, volcanoes).