Rivers flowed WHEN it rained *
Which, as I said below, was about 1% of the time (not 1 day in 100, but 1 century in 10,000 years). Clays DID form. Surface life was technically possible, if difficult. Subsurface life should have been entirely straightforward - so far a life ever is...
* Actually, it could have mostly been snow that fell, and basal melting or a springtime thaw with a brief rush of water down the rivers, like the break-up in Alaska and Siberia...