evidence: The tilt of the Earth’s rotational axis is what gives us seasons. We have summer in the northern hemisphere when the Earth is in the part of its orbit where the northern hemisphere is pointed towards the sun, and summer in the southern hemisphere summer when the southern hemisphere is pointed towards the sun. At times of greater tilt, the seasons are slightly more exaggerated than they are now (colder winters, hotter summers). At times of lesser tilt, they are less exaggerated (warmer winters, cooler summers). The tilt angle varies on a cycle of 40,000 years. [...] During the middle part of the 20th century marine scientists and geologists started drilling into the soft sediments on the sea floor. The resulting cores provided a wealth of information about past marine life and conditions of sedimentation, and based on isotopic analyses, the temperature of the water. A key paper, published in 1976, clearly showed the relationship between those temperature variations and the astronomical cycles. The authors wrote: "It is concluded that changes in the earth’s orbital geometry are the fundamental cause of the succession of Quaternary ice ages."[2] This was the turning point for the Milanković concept. Since then, thousands of studies of climate variations have corroborated the key role played by the Milanković cycles, both during the Quaternary glaciations and in other climate cycles (e.g., Monsoons) for millions of years before then.