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Credit: Google Maps Africa, Asia, Australia, Antarctica, North and South America, Europe—and the Maritime Continent. Never heard of the last one? That's because it's not a continent made of land. In fact, it's the largest warm tropical sea in the world, lapping against the shores of Indonesia, Malaysia, Papua New Guinea, the Philippines and smaller…

Left: Satellite image of the submerged northwest shelf region. Right: Drowned landscape map of the study area. Credit: US Geological Survey, Geoscience Australia For much of the 65,000 years of Australia's human history, the now-submerged northwest continental shelf connected the Kimberley and western Arnhem Land. This vast, habitable realm covered nearly 390,000 square kilometers, an area one-and-a-half times larger than New…