Archaeologists in Mexico found stone tools and other signs that people were living in North America 30,000 years ago, much earlier than widely believed, according to new research reshaping the debate over the origins of people in the Americas.In a study reported Wednesday, scientists led by archaeologist Ciprian Ardelean at Mexico’s University of Zacatecas said that they had unearthed hundreds of unusual green limestone spear points, blades and other implements from a lofty cavern in the central Mexican highlands. For wandering hunter-gatherers, the cave served as a makeshift tool shed possibly beginning as early as about 33,000 years ago, the...