Researchers find clues to glacial mystery on the bed of the Atlantic Ocean
About a million years ago, something big happened to the planet. There was a major shift in the response of Earth's climate system to variations in our orbit around the Sun. That shift is called the Mid-Pleistocene Transition, or MPT. Before the MPT, cycles between colder glacial and warmer interglacial periods happened every 41,000 years. After, glacial periods became more intense -- intense enough to form ice sheets in the Northern Hemisphere that lasted 100,000 years. That gave Earth the regular ice age cycles that have persisted into human time.