Many years ago when considering the many motions of the Earth for a class in Basic Astronomy, I learnt about the “Milankovitch Cycles” which were based on climate changes due to shifts in the inclination of the Earth’s axis and the effects of the Sun, the Moon and the planets on its orbit. We, if we think of it at all, tend to consider the Earth, its axis inclined at an angle of 23½°, smoothly orbiting the Sun at the rather amazing velocity, by everyday standards, of 33 km/sec. Before Galileo, it was thought that the Earth did not move as, if it did, we would all fly off into space.

Galileo demonstrated that this would not occur because we are moving at the same velocity as the Earth and pointed out that a stone dropped from the top of a the mast of a moving ship drops to the bottom of the mast and does not fall backwards into the sea for the same reason. It does not seem that the Earth moves, we do not experience any movement under our feet but Galileo knew that he was correct and went into house arrest because of his heliocentric theory of the solar system muttering “but it DOES move”.

The Earth’s movement in orbit is affected by the gravitational attraction of bodies in its vicinity- the Moon, the Sun, the planets – and Malankovitch  proposed that these relatively small changes in its orbit were cyclic and had a cyclic effect on climate which resulted in the Ice Ages. The gradual changes in the inclination of the Earth’s axis also had a cyclic effect according to Malankovitch who spent many year working out the effects of these changes on the amount of sunlight falling on the Earth and found that there were  cycles of 20,000, 41,000 and 100,000 years which correlated with the proposed occurrence of ice ages. 

The effects of relatively small changes in  the amount of sunlight falling on the Earth on climate had previously been proposed by James Croll in the mid 19^th century  but its substantiation was due to the painstaking investigations of  the effects of distance and  angle of the Sun on solar radiation by Milankovitch  many years later. Milankovitch also proposed that, under certain conditions, the snow in high latitudes would not melt but would build up into sheets which reflected sunlight and thus make the climate colder for a period of time. Although the “Milanlovitch Cycles” were included in text books on climate, they were by no means universally accepted by climatologists of the time.

Considerable work had been carried out on ice ages by scientists in different disciplines who studied deep sea sediments, cores drilled through the Antarctic icecap, massive volcanic eruptions and sedimentary surface features among many other fields of research  using radiocarbon dating, the decay of radioactive elements, the presence of marine organisms peculiar to certain temperature limits, the identification of pollen grains and the in depth analysis of cores drilled from both the sea bed and the southern ice cap which spanned an entire glacial period. It became obvious that many ice ages had occurred on the Earth over time in what was turning out to be a cyclic pattern but there was no universal agreement that these cycles corresponded with the Milankovitch cycles.