Slushball Earth hypothesis thumb|thumbtime=0:20|right|Simulation with liquid water around the equator 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 struggled to accommodate global ice cover without fundamental changes in the laws and constants which govern the planet.
sluShbALl EARtH HypotHEsis ThuMb|ThumbTime=0:20|rIGhT|sIMULation With lIquid wATER arounD THe eqUaTor 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 strUgGlEd TO accomMODAtE global icE coVEr without funDamENtAl chAngEs IN tHe laws And coNstAnts whICh gOvern ThE plaNeT.