Nancy Unger is professor of history at Santa Clara University and the author of "Beyond Nature's Housekeepers: American Women in Environmental History."(CNN) -- Earth Day is the time of year to hear the usual polarized debates between liberals who lament humanity's reckless use of natural resources and conservatives who deny any human role in climate change and echo Sarah Palin's call for industry to "drill, baby, drill."This division is familiar, but it hasn't always been this way. After all, it was President Nixon who established the Environmental Protection Agency and signed the Clean Air Act. Long before that, social conservatives were in the vanguard of environmental activism in the United States, in part because of their traditional views about women.