Geologists have incorrectly assumed that the Earth has had all its water since its beginning. It is demonstrably incorrect yet it remains the primary reason why we do not understand our past.
There was a worldwide flood, and it was recent.
See here for some ideas: http://www.threeimpacts-twoevents.com/wp-content/uploads/2013/08/COMET-IMPACT-ANALYSIS-AND-EFFECTS-20Aug2013.pdf
Mars is missing vast oceans of water - much of this fell to earth during encounters with Mars (Mars the god of war for good reason) only a few millennia ago. It is still falling to earth in the form of noctilucent clouds would be my stance. http://en.wikipedia.org/wiki/Noctilucent_cloud