A division of areological time, lasting from 4.60 Gy to 3.50 Gy in the Hartmann–Tanaka Model and 4.60 Gy to 3.80 Gy in the Neukum–Wise Model, and divided into three epochs: Lower Noachian (4.60–3.92 or 4.60–4.50 Gy); Middle Noachian (3.92–3.85 or 4.50–4.30 Gy); and Upper Noachian (3.85–3.50 or 4.30–3.80 Gy).