By the early years of the twentieth century, as the geology of the continents began to be better known, it was realized that Permian and Precambrian glacial deposits occur virtually on all continents and at low latitudes.
To the 'permanentists' who believed in an Earth where continents and oceans remain static, the global scattering of glacial rocks required enormous ice sheets expanding into low latitudes (Grabau, 1920; Coleman, 1926, 1932, 1939).
Second, Wegener had indirectly questioned the combined weight of their expertise by daring to question the supposed glacial origin of the famous 'Squantum Tillite' found near Boston.
Cotton (1942) referred to glaciation as a 'climatic accident' and Pauly (1957) referred to 'world-wide abnormal climates" Such events were regarded as being superimposed on static continents where deep glacial erosion and deposition of coarse bouldery sediments such as tills simply interrupted an otherwise orderly Davisian cycle of landscape and sediment evolution from youth to maturity.
The depositional model then available was that of continental glacial deposition where tills, glaciolacustrine and outwash deposits record the climatically driven waxing and waning of ice sheets.
It was soon appreciated that not all poorly sorted rocks are glacial tillites deposited below glaciers on elevated continental surfaces; many are non-glacial deep-marine mass-flow deposits interbedded with turbidites (Fig.
Schermerhorn (1974) led the charge in re-examining ancient 'glacial' deposits in the light of their tectonic and basinal setting.
Hambrey and Harland's (1981) very impressive Earth's Pre-Pleistocene Glacial Record compiled the known rock record but perhaps missed the opportunity to place it in the context of plate tectonics and emerging paleogeographic reconstructions.
This is decades after sedimentologists began to highlight the simplistic interpretation of ancient 'glacial' strata and the need for comprehensive facies and basin analysis studies.
(1999) for whom 'the global distribution of glacial deposits of Neoproterozoic age suggests that the ice sheet of the time developed even to the equatorial area'.
Of all the climatic factors that seem to vary between glacial and interglacial periods, the amounts of dust trapped in polar ice sheets underwent the largest change, Broecker notes.
Broecker also points out that loess, which was generated in copious amounts during the peaks of the glacial periods, wasn't produced during interglacials.