During the last Ice Age, glaciers covered the ocean as well as the land, killing photosynthetic algae that lived in the ocean. With algae in small numbers, they were able to remove only a fraction of CO2 from the atmosphere. With no check on its accumulation, CO2 increased in the atmosphere, causing the greenhouse effect. The greenhouse effect ended the Late Proterozoic Ice Age roughly 550 million years ago, inaugurating a new warm period. The lush plant growth of the Carboniferous Era (350-280 million years ago) confirms that the climate was warm and that CO2, essential for plant growth, was abundant. Around 230 million years ago, the continents gathered into a single landmass called Pangea. Being near the equator, Pangea's climate was tropical. Even warmer was the Cretaceous Era (135-65 million years ago). Temperatures soared 20 degrees F (11 degrees C) warmer than in the current era. Forests covered Antarctica. Ocean currents again carried warm water to the poles. The transit of warm water to the poles caused polar water to be only 40 degrees F (4 degrees C) cooler than equatorial waters. The difference today is 75 degrees F (24 degrees C). The water at the bottom of the ocean, now near freezing, was then 25 degrees F (14 degrees C) warmer. Coral reef, which requires warm water to survive, grew 1,000 mi. (1,609 km.) closer to the poles than it does today. Antarctica was warm enough to support the growth of forests.
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