The snowball Earth hypothesis suggests that Earth experienced a global glaciation event, with ice sheets extending to the equator. This hypothesis challenges the traditional view that Earth's orbital obliquity was low, making the tropics warmer than the poles. Instead, it proposes that climate cooling led to a runaway ice-albedo feedback, creating a 'snowball' Earth. The hypothesis is supported by geological evidence, including the abrupt onsets and terminations of glacial events, the association of these events with large negative δ¹³C shifts in seawater proxies, and the deposition of cap carbonates during post-glacial sea-level rise. The snowball hypothesis also predicts that a large greenhouse effect would be necessary to melt the ice, leading to a transient post-glacial regime of enhanced carbonate and silicate weathering, which could explain the widespread occurrence of cap carbonates. The hypothesis is further supported by the presence of cap carbonates, which are interpreted as the 'smoke' of a snowball Earth, with the 'gun' being the unusual distribution of land masses in the middle and low latitudes, which increased the planetary albedo and set the stage for snowball events. The hypothesis is also supported by the fact that the Neoproterozoic glacial record shows a high degree of synchronicity, which is consistent with the global scale of the climatic fluctuations. The snowball hypothesis has been tested through various geological and geochemical analyses, including the study of carbon isotopes and cap carbonates, which have provided strong support for the hypothesis. The hypothesis suggests that the Earth's climate was highly unstable, with the potential to rapidly switch between 'ice house' and 'greenhouse' states. The snowball hypothesis is a significant contribution to our understanding of Earth's climate history and the factors that have shaped the planet's environment over geological time scales.The snowball Earth hypothesis suggests that Earth experienced a global glaciation event, with ice sheets extending to the equator. This hypothesis challenges the traditional view that Earth's orbital obliquity was low, making the tropics warmer than the poles. Instead, it proposes that climate cooling led to a runaway ice-albedo feedback, creating a 'snowball' Earth. The hypothesis is supported by geological evidence, including the abrupt onsets and terminations of glacial events, the association of these events with large negative δ¹³C shifts in seawater proxies, and the deposition of cap carbonates during post-glacial sea-level rise. The snowball hypothesis also predicts that a large greenhouse effect would be necessary to melt the ice, leading to a transient post-glacial regime of enhanced carbonate and silicate weathering, which could explain the widespread occurrence of cap carbonates. The hypothesis is further supported by the presence of cap carbonates, which are interpreted as the 'smoke' of a snowball Earth, with the 'gun' being the unusual distribution of land masses in the middle and low latitudes, which increased the planetary albedo and set the stage for snowball events. The hypothesis is also supported by the fact that the Neoproterozoic glacial record shows a high degree of synchronicity, which is consistent with the global scale of the climatic fluctuations. The snowball hypothesis has been tested through various geological and geochemical analyses, including the study of carbon isotopes and cap carbonates, which have provided strong support for the hypothesis. The hypothesis suggests that the Earth's climate was highly unstable, with the potential to rapidly switch between 'ice house' and 'greenhouse' states. The snowball hypothesis is a significant contribution to our understanding of Earth's climate history and the factors that have shaped the planet's environment over geological time scales.