explosion, which would cause a relatively rapid reoxygenation of the atmosphere, which may have contributed to the rise of the Ediacaran biota and the subsequent Cambrian explosion—a higher oxygen concentration allowing large multicellular lifeforms to develop. Although the positive feedback loop would melt the ice in geological short order, perhaps less than 1,000 years, replenishment of atmospheric oxygen and depletion of the levels would take further millennia. It is possible that carbon dioxide levels fell enough for Earth to freeze again; this cycle may have repeated until the continents had drifted to more polar latitudes. More recent evidence suggests that with colder oceanic temperatures, the resulting higher ability of the oceans to dissolve gases led to the carbon content of sea water being more quickly oxidized to carbon dioxide. This leads directly to an increase of atmospheric carbon dioxide, enhanced greenhouse warming of Earth's surface, and the prevention of a total snowball state. During millions of years, cryoconite would have accumulated on and inside the ice. Psychrophilic microorganisms, volcanic ash and dust from ice-free locations would settle on ice covering several million square kilometers. Once the ice started to melt, these layers would become visible and color the icy surfaces dark, helping to accelerate the process. Also, ultraviolet light from the Sun produced hydrogen peroxide (H2O2) when it hit water molecules. Normally H2O2 breaks down in sunlight, but some would have been trapped inside the ice. When the glaciers started to melt, it would have been released in both the ocean and the atmosphere, where it was split into water and oxygen molecules, increasing atmospheric oxygen. Slushball Earth hypothesis While the presence of glaciers is not disputed, the idea that the entire planet was covered in ice is more contentious, leading some scientists to posit a "slushball Earth", in which a band of ice-free, or ice-thin, waters remains around the equator, allowing for a continued hydrologic cycle. This hypothesis appeals to scientists who observe certain features of the sedimentary record that can only be formed under open water, or rapidly moving ice (which would require somewhere ice-free to move to). Recent research observed geochemical cyclicity in clastic rocks, showing that the "snowball" periods were punctuated by warm spells, similar to ice age cycles in recent Earth history. Attempts to construct computer models of a snowball Earth have also struggled to accommodate global ice cover without fundamental changes in the laws