Alternative theories for low-latitude glaciation
Kirschvink was not the first to wrestle with the low-latitude Elatina results. George Williams (1975, 1993, 2000) had long advocated a large (>54°) orbital obliquity, or tilt (the angle between the Earth's axes of rotation and orbit around the sun), to account for low-latitude glaciation in conjunction with inferred strong equatorial seasonality during the Elatina glaciation (Williams and Tonkin, 1985; Williams, 1998). In theory, obliquity could have varied chaotically within 60-90° following the early lunar-forming impact event, but a low obliquity, once achieved, is self-stabilizing through the gravitational interaction of the Moon and the Earth's equatorial bulge (Laskar et al., 1993). Williams (1993) postulates a sharp decrease in orbital obliquity after 600 Ma, with resultant moderation of the seasonal climate cycle giving rise to the metazoa (Williams, 1993). With an obliquity >54°, mean annual temperatures are lower around the equator than at the poles (Williams, 1975; Hunt, 1982; Oglesby and Ogg, 1999; Jenkins, 2000), making glaciation more probable at lower latitudes (Williams, 1975). Summer insolation is so large in the polar regions (the sun staying high in the sky throughout the diurnal cycle) that surface temperatures over land areas might exceed the boiling point of water (Oglesby and Ogg, 1999). The tropics, although cooler over all, would have two hot seasons near equinox, when insolation would be indistinguishable from the hottest tropical seasons with low obliquity (Ogelsby and Ogg, 1999). Indeed, hot summers and strong seasonality make glaciation problematic at any latitude with large obliquities (Hoffman and Maloof, 1999). It does, however, provide a ready but non-unique (Maloof et al., 2002) explanation for the existence of well-developed, periglacial, sand-wedge polygons in the Elatina Formation (Williams and Tonkin, 1985). These structures are most easily explained as resulting from large seasonal oscillations in soil temperature (Lachenbruch, 1962), which should not occur near the equator if the obliquity was close to its present value of 23.5°. On the other hand, a persistent large obliquity does not explain the characteristically abrupt onsets and terminations of LNGD (Hambrey and Harland, 1981; Preiss, 1985; Narbonne and Aitken, 1995; Hoffmann and Prave, 1996; Hoffman et al., 1998a). Nor does it account for the close association of LNGD with carbonates, because the "redistribution of the radiant energy balance to polar latitudes should also move the carbonate belts from equatorial latitudes to the poles, where the glaciers (in William's model) should not encounter them" (Kirschvink, 1992). The dynamics of the postulated obliquity reduction after 600 Ma remain conjectural (Williams, 1993; Ito et al., 1995; Néron de Surgy and Laskar, 1997; Williams et al., 1998; Pais et al., 1999).

Richard Sheldon (1984) postulated that orbiting ice rings episodically collapsed into the atmosphere, transiently shielding sunlight and giving rise to glaciers at low latitudes. The theory strives to explain iron formations and cap carbonates, but does not adequately account for low-latitude glaciation. Due to orbital obliquity, equatorial ice rings will cast shadows only on the winter hemisphere (see Fig. 2 in Sheldon, 1984). Glaciation depends critically on cool summers, not cold winters (Köppen and Wegener, 1924), as it is contingent on a fraction of the annual snowfall surviving the melting seasons.