The Martian geologic timescale has three broad epochs defined by the number of impact craters on the surface; older surfaces have more craters. The epochs are named after places on Mars that belong to those time periods. The precice timing of these periods is not known because there are several competing models describing the rate of meteor fall on Mars, dates given here are approximate. From oldest to youngest, the time periods are:

• Noachian epoch (named after Noachis Terra ): Formation of Mars to between 3800 and 3500 million years ago. Noachian age surfaces are scarred by many large impact craters. The Tharsis bulge is thought to have formed during this period, with extensive flooding by liquid water late in the epoch.
• Hesperian epoch (named after Hesperia Planum ): 3500 million years ago to 1800 million years ago. The Hesperian epoch is marked by the formation of extensive lava plains.
• Amazonian epoch (named after Amazonis Planitia ): 1800 million years ago to present. Amazonian regions have few meteorite impact craters but are otherwise are quite varied. Olympus Mons formed during this period along with lava flows elsewhere on Mars.