Historians categorize time into different scales in order to study _ activity over large periods of time. A. Earth B. All animal C. land animal D. human

The answer is D. History is a social science and an academic discipline that studies human activity over large periods of time. The common and general categories that historians traditionally have made in order to differentiate periods of History are:

Prehistory: before the invention of writing around 3500 BC

Antiquity: from 3500 to the fall of the Western Roman Empire in 475 AC

Middle Ages: from 475 AC to the fall of the Byzantine Empire in 1453.

Modern Age: from 1453 to current time.

The are several subcategories and alternative ways of differentiating time scales according to different aspects and concepts.