Eugene W. Hilgard, in 1892, had related soil and climate in the United States in the same manner, and by the 1950s analysis of Quaternary stratigraphy to monitor recent environmental changes in the northern hemisphere had become firmly established. These developments have allowed soil fossils to be classified according to USDA soil taxonomy quite easily with all recent soils. Interest in earlier soil fossils was much slower to grow, but has steadily developed since the 1960s owing to the development of such techniques as X-ray diffraction which permit their classification. This has allowed many developments in paleoecology and paleogeography to take place because the soils' chemistry can provide a good deal of evidence as to how life moved onto land during the Paleozoic era.