A division of areological time, lasting from 3.50 Gy to 1.80 Gy ago in the Hartmann–Tanaka Model and 3.80 Gy to 3.55 Gy ago in the Neukum–Wise Model, and divided into two epochs: Lower Hesperian (3.50–3.10 or 3.80–3.70 Gy ago); and Upper Hesperian (3.10–1.80 or 3.70–3.55 Gy ago).