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based on whether there are glaciers on the planet, and for most of Earth's history it has been in a greenhouse period with little or no permanent ice. Over the very long term, Earth is currently in an icehouse period called the Late Cenozoic Ice Age, which started 34 million years ago. There have been colder and warmer periods within this ice age, and the term is also applied to the Quaternary glaciation, which started 2.58 million years ago. Within

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