ON STUDIES OF SNOWBALL EARTH

Had Earth ever been completely covered by snow and ice and become a giant "snowball Earth" during the Neoproterozoic about 600~700 million years before? If it had,what caused this global freezing? What led it to melt? What had the violate climate changes during the Neoproterozoic impacted on the Cambrian life explosion? In the past few years,these problems have drawn extensive studies and intensive controversies in the fields of paleo-geology,paleontology,and paleoclimatology.According to existing results,it is generally thought that during the Neoproterozoic Earth had experienced several most severe global glaciations in Earth's history.However,it needs further geological and paleo-biological evidence to prove whether Earth had been completely frozen or not;numerical simulations with various external forcings showed that the formation of a hard "snowball Earth" is almost impossible,and if Earth runs into complete freezing,it is hard to get back out;there are two controversial points of views that such violate climate changes during the Neoproterozoic might have important impacts on the Cambrian life explosion.One is that the climate changes can induce mutations that fuel biological innovation,and the other one is that the impacts are on ecosystems.