Part of the Martian Geologic Timescale
Noachian Period - Hesperian Period - Amazonian Period
The Hesperian Period is the third period of the Martian Geologic Timescale. This period begins with the formation of the Hesperia Planum, and ends with the formation of the Vastitas Borealis. By the Hesperian, the wet and warm Mars had begun the transition into its current dry and cold state. Volcanism would become the primary geologic process of the period after impacts became much less frequent after the end of the Late Heavy Bombardment in the Noachian, a process that would continue throughout the Hesperian, going from 80 times the current rate at the beginning to the present rate at the end. Despite its (at least once though to be) dry conditions, there is evidence that flooding was still frequent, and ice existed on the planet. While it was likely still much drier than in the Noachian Period, the discovery of a large ancient river on Mars dated to 3500 MYA was announced in 2013. At at least one point, the river was around one-thousand feet deep and close to four-and-a-half miles wide. The river as a whole stretches for over nine-hundred miles. The atmosphere thinned to its current state during the Late Hesperian. The Valles Marineris and Olympus Mons formed during this period.
The Hesperian is subdivided into two epochs: the Early Hesperian and the Late Hesperian.
Hesperian Timescale:
Hesperian Period - 3700-3000 MYA
-Early Hesperian Epoch - 3700-3400 MYA
-Late Hesperian Epoch - 3400-3000 MYA