By 21 million years ago south america and australia

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By 21 million years ago, South America and Australia have separated from Antarctica— plates are in motion, continents are separating Antarctica now isolated by circumpolar southern ocean near southern pole (cold). Now  opened Drake Passage allowed cold (dense) Antarctic waters to flow into the Atlantic  Ocean and sink (called Antarctic Bottom Water AABW)  Meanwhile way up in Northern Hemisphere, as Europe separated from North America,  cold (dense) ocean water (North Atlantic Deep Water NADW) flowed across the Iceland- Faroes Ridge and into the Atlantic Ocean basin NADW flowed south near the bottom of Atlantic Ocean AABW flowed north near the bottom of Atlantic Ocean Slightly warmer (less dense) NADW flowed over AABW—upwelled near Antarctica— causing moisture (snow, ice) to form in Antarctica So glacial ice was forming in Antarctica, but not yet in Northern Hemisphere, however  by 2-3 million years ago isthmus of Panama joined North America to South America.  Closed off circulation between the Pacific and Atlantic Oceans Closed circulation created warm ocean surface current (gulf stream) that brought  warmer water (moisture) to northern parts of northern parts of northern hemisphere— ice formed! Pleistocene Ice Age started! Glaciers, Pleistocene Ice Age These climatic variations are due to two major processes Longer term fluctuations in climate are due to plate tectonics
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