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The Serbian scientist Milankovi? described during World War one the cyclic variations in the orbit and tilt of the Earth. Only in 1976, the theory was accepted by most scientists because then evidence was found in the stratigraphy. Later, evidence for his theory was found in drilled ice cores from Antarctica.
There are three different cycles that play a role, each with their own periodicity:
- Cycle of the eccentricity of the Earth's orbit ( period of 100,000 years)
- Cycle of the obliquity of the Earth's axis (period 41,000 years)
- Cycle of the precession of the Earth's axis (period 26,000 years)
These variations in the orbit and tilt of the Earth have major implications for the global climate. Due to changes in the Earth's position and orbit, there are periods of more and less solar radiation on Earth. In addition, this solar radiation is periodically distributed differently over the Earth. This has major implications for the climate. These cycles have played a major role in the periodic occurence of glaciations during the Pleistocene. In the stratigraphy cyclic variations which are associated with the Milankovi? cycles were found in deposits from many periods.
The eccentricity is the extent to which the orbit of the Earth around the sun is more elliptical, or more circular. Because the Earth is sometimes closer to the sun than usual this results in climate change.
The obliquity is the angle of the Earth's axis relative to the plane of the Earth's orbit around the sun. The angle of the Earth's axis causes the occurrence of seasons on Earth. A larger angle leeds to more differences between seasons, and a different distribution of solar radiation on Earth. This cycle can cause the start of an ice age.
The precession is the spinning movement of the position of the axis. The consequences are the same as the cycle of obliquity.
Because the three cycles simultaneously affect the climate on Earth, and because they different periodicity, this results to a complex series of climate changes in the course of time. Climate change often has a direct impact on sea level. The stratigraphy shows this as transgression and regression periods. In the field, this may well be seen as a series of alternating thinning layers and thickening layers.
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