Lele, Ajey (2018). Disruptive Technologies for the Militaries and Security (на језику: енглески). Springer. стр. xvi. ISBN978-981-13-3384-2. Приступљено 10. 2. 2022. „Some [researchers] have related the progression of mankind directly (or indirectly) based on technology-connected parameters like the three-age system (labelling of history into time periods divisible by three), i.e. Stone Age, Bronze Age and Iron Age. At present, the era of Industrial Age, Information Age and Digital Age is in vogue.”
Kipfer, Barbara Ann (2000). Encyclopedic Dictionary of Archaeology (на језику: енглески). Springer Science & Business Media. стр. 564. ISBN978-0-306-46158-3. Приступљено 10. 2. 2022. „Three-Age system: The division of human prehistory into three successive stages – Stone Age, Bronze Age, and Iron Age – based on the main type of material used in tools of the period. […] The Ages are only developmental stages, and some areas skipped one or more of the stages. At first entirely hypothetical, these divisions were later confirmed by archaeological observations.”
