Recent studies of ice ageschoose one: a. suggest that the entire earth was covered by glacial ice in the late paleozoic, called "snowball earth."b. have dated events by analyzing wood trapped in glacial deposits, the oxygen-isotope ratio in marine sediments, and tillite deposits. c. have indicated the formation of paleosols during glacial periods, suggesting that glaciers formed under temperate conditions in some regions. d. reveal fewer large ice ages, fewer subdivisions, and less complexity than was originally thought.