  Early Mars climate research has well-defined goals (Mars Exploration Program
Analysis Group 2018). Achieving these goals requires geologists and climate
modelers to coordinate. Coordination is easier if results are expressed in
terms of well-defined parameters. Key parameters include the following
quantitative geologic constraints. (1) Cumulative post-3.4 Ga
precipitation-sourced water runoff in some places exceeded 1 km column. (2)
There is no single Early Mars climate problem: the traces of $\ge$2
river-forming periods are seen. Relative to rivers that formed earlier in Mars
history, rivers that formed later in Mars history are found preferentially at
lower elevations, and show a stronger dependence on latitude. (3) The duration
of the longest individual river-forming climate was >(10$^2$-10$^3$) yr, based
on paleolake hydrology. (4) Peak runoff production was >0.1 mm/hr. However, (5)
peak runoff production was intermittent, sustained (in a given catchment) for
only <10% of the duration of river-forming climates. (6) The cumulative number
of wet years during the valley-network-forming period was >10$^5$ yr. (7)
Post-Noachian light-toned, layered sedimentary rocks took >10$^7$ yr to
accumulate. However, (8) an "average" place on Mars saw water for <10$^7$ yr
after the Noachian, suggesting that the river-forming climates were
interspersed with long globally-dry intervals. (9) Geologic proxies for Early
Mars atmospheric pressure indicate pressure was not less than 0.012 bar but not
much more than 1 bar. A truth table of these geologic constraints versus
currently published climate models shows that the late persistence of
river-forming climates, combined with the long duration of individual lake
forming climates, is a challenge for most models.
