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

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.

Climate Simulations of Early Mars With Estimated Precipitation, Runoff, and Erosion Rates

“…An early Mars that was relatively warm is not only supported by these climate modeling simulations, but also by the geologic record itself (Ramirez & Craddock, ). The absence of glacial features, including eskers, kames, and frost wedges in ancient valley terrains all suggest that the valleys were not formed in a cold and icy climate.…”

“…Although Mars is mostly dry and possesses a tenuous atmosphere today, this was not the case~3.8-4 billion years ago when the geologic evidence reveals a landscape filled with many fluvial features, including deltas, alluvial fans, ancient shorelines, modified craters, and of course, the enigmatic valley networks (e.g., Craddock & Howard, 2002;Fassett & Head, 2008;Howard et al, 2005;Irwin et al, 2011;Masursky, 1973;Parker et al, 1993). This geologic evidence is strongly indicative of a once warmer and wetter climate than is the case today (e.g., Craddock & Howard, 2002;Ramirez & Craddock, 2018).…”

Survivability of Soil and Permafrost Microbial Communities after Irradiation with Accelerated Electrons under Simulated Martian and Open Space Conditions

“…The modern concept of the Mars evolution assumes a scenario of the planet's development according to the terrestrial type with the possible emergence of the biosphere [24][25][26][27][28]. The impact of radiation could contribute to the origin of life, being, possibly, a key factor [108].…”

“…Laboratory experiments do not allow for studying the long accumulation of doses of relatively low intensity in the microbial biomass of natural soil. The main question of the present study is how long the biosphere of Mars could be maintained after the supposed catastrophic change in planetary conditions [24][25][26][27][28][29], the gradual loss of the atmosphere [30], and the formation of a modern climate.…”

Quantitative High‐Resolution Reexamination of a Hypothesized Ocean Shoreline in Cydonia Mensae on Mars

“…These observations, coupled with hand‐mapped contacts along the edges of the northern plains on comparatively low‐resolution images, led to the interpretation of these contacts as paleoshorelines (Parker et al, , ). The question of whether or not such an ocean (or oceans) existed has profound implications for the past climate of Mars (e.g., Banfield et al, ; Jakosky & Phillips, ; Lammer et al, ; Ramirez & Craddock, ), the possibility of the planet harboring ancient life (e.g., Beaty et al, ), and the evolution and role of liquid water in its surficial geology (e.g., Carr & Head, , ).…”