Widespread surface weathering on early Mars: A case for a warmer and wetter climate

•Specific clay stratigraphies are investigated at a global scale on Mars.•Over 100 deposits consistent with terrestrial pedogenic sequences have been found.•Observations suggest widespread surface aqueous weathering on Mars >3.6Ga. Early Mars (>3Ga) underwent aqueous alteration as evidenced by fluvial/lacustrine morphologies and the recent discovery of widespread hydrous clays. Despite compelling evidence for diverse and localized aqueous environments, the possibility for sustained liquid water globally on the martian surface and over geological timescales is still highly debated. Instead, a durably cold and dry Mars scenario is often proposed. By studying specific Fe/Mg and Al-rich clay stratigraphies on Mars by means of a planetary scale orbital investigation, we present new evidence that Mars experienced an early era (>3.7Ga) of widespread aqueous alteration consistent with surface weathering.