During which period did valley networks suggest denser atmosphere and water on Mars?

The Noachian Period is characterized by the presence of valley networks on Mars, which are channels that appear to have been shaped by flowing liquid water. This geological evidence suggests that during this time, Mars likely had a denser atmosphere and liquid water on its surface, conditions that would have supported a more Earth-like environment.

The formation of these valley networks indicates that there was enough atmospheric pressure to allow liquid water to exist for an extended period, leading to erosion and the development of these features. This is significant because it aligns with theories suggesting that Mars once had a climate suitable for sustaining life, with potential rivers and lakes.

In contrast, the Hesperian Period is noted for volcanic activity and possible changes in climate, which may have diminished water presence, and the Amazonian Period is characterized by a dry and cold climate with very little water activity. The current era of Mars does not suggest a history of a dense atmosphere or surface water, as it is primarily known for its arid and cold conditions.