When soil science was first founded, climate was considered one of the most important factors regarding the formation of soil. For instance, temperate regions have widespread acidic sand Spodosols, and in tropical regions red clayey Oxisols are common. The tendency to use climatic data for the classification of soils has been challenged by efforts to base the classification of soil on observable features within the soils. This tendency is unfortunate because paleoclimates cannot be interpreted from paleosols identified using paleoclimatic data. Fortunately, the identification of paleosols using climatic data is changing. For example, Aridisols have been redefined (Soil Survey Staff 1998) as soils that possess a calcic horizon of less than 1 meter in depth.