The Earth's glaciers are reportedly in a rapid melting phase. However, some scientists believe that in ancient times, the earth fell into a deep frozen state called "snowball earth", when the ice cap almost completely covered the entire earth. However, the earth appeared The number of deep freezes, the extent of extension, and the speed at which the earth turns into a snowball have been unsolved. At present, scientists have analyzed the latest rock sequences discovered in Ethiopia, and the results show that the "snowball earth" was only This discovery supports the theoretical model of snowball glaciers, which suggests that once the ice extends to 30 degrees of Earth's latitude, rapid global glaciation occurs. Which of the following can we learn from this text? ['Causes of rapid glacial action.', 'Formation speed of "Snowball Earth".', 'Number of deep freezes on Earth.', 'Specific age of "Snowball Earth".']