Archaeological exploration of the pre-Islamic period of Afghanistan began in Afghanistan in earnest after World War II and proceeded until the late 1970s when the nation was invaded by the Soviet Union. Archaeologists and historians suggest that humans were living in Afghanistan at least 50,000 years ago, and that farming communities of the region were among the earliest in the world. Urbanized culture has existed in the land from between 3000 and 2000 BC. Artifacts typical of the Paleolithic, Mesolithic, Neolithic, Bronze, and Iron ages have been found inside Afghanistan.