in individual regions, scientists can use radiometric dating to determine the age of a tool much more precisely. for example, acheulean methods did not reach europe until around 400,000 years ago. in smaller study areas, scientists can narrow down a tool's age even more. however, numerical dates can be misleading. it is common to associate examples of this early human tool industry with one or more glacial or interglacial periods, or with a particular species of early human. the earliest user of acheulean tools was "homo ergaster," who first appeared about 1.8 million years ago. some researchers prefer to call these hominids "early homo erectus". later forms of early humans also used acheulean techniques. these are described below.