The geological and climatological case for a warmer and wetter early Mars

TL;DR

This paper argues that early Mars likely had a warm, semi-arid climate capable of supporting liquid water, based on geological evidence and climate modeling, challenging the idea of a predominantly cold Mars.

Contribution

It presents a comprehensive analysis combining geological evidence and climate models to support a warm, semi-arid early Mars climate hypothesis.

Findings

Early Mars had liquid water on its surface 4 billion years ago.

A warm, semi-arid climate best explains geological features.

Cold and icy climate with transient warming episodes is less consistent.

Abstract

The climate of early Mars remains a topic of intense debate. Ancient terrains preserve landscapes consistent with stream channels, lake basins, and possibly even oceans, and thus the presence of liquid water flowing on the Martian surface 4 billion years ago. However, despite the geological evidence, determining how long climatic conditions supporting liquid water lasted remains uncertain. Climate models have struggled to generate sufficiently warm surface conditions given the faint young Sun - even assuming a denser early atmosphere. A warm climate could have potentially been sustained by supplementing atmospheric CO2 and H2O warming with either secondary greenhouse gases or clouds. Alternatively, the Martian climate could have been predominantly cold and icy, with transient warming episodes triggered by meteoritic impacts, volcanic eruptions, methane bursts, or limit cycles. Here, we argue that a warm and semi-arid climate capable of producing rain is most consistent with the geological and climatological evidence.