rom the Geological Society of London (1990), and the National Medal of Science (1996).
             Broecker's image of the conveyor belt is somewhat simplified. The ocean conveyor is propelled by the sinking of cold, salty (and therefore denser) waters in the North Atlantic Ocean. This band of deep water flowing south down through the depths of the Atlantic spreads into the Indian and Pacific oceans where it wells to the surface and mixes with other warm tropical waters, it also helps to pull warm, salty Gulf stream waters northward. The warm waters return back to the North Atlantic where mixed with colder Greenland waters and driven by bitter winds it becomes gradually colder & saltier once again sinking into the deep. In reality much of the water that sinks in the Atlantic never leaves and other eddies and gyres across the oceans mean that this really is a simplified image of the conveyor belt but essentially the basic idea is true. The conveyor "transports heat into the North Atlantic and salt out of it".
             The earth's past is full of dramatic climate changes. Many glacial advances and retreats have occurred during the last billion years of Earth history. Large, important glaciations occurred during the late Proterozoic (between about800 and 600 million years ago), during the Pennsylvanian and Permian (between about 350 and 250 million years ago), and the late Neogene to Quaternary (the last 4 million years). Somewhat less extensive glaciations occurred duri
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