This is part one of a two part question. Part two can be found her (How to Cause a Hydrosphere Apocalypse Part II The Great Flood)
Desert planets are a staple of science fiction. And while we have worlds like Luna, Mars and Mercury to show that barren planets are decently common, one fascinating scenario I keep running into is the idea that once these dust balls were living breathing worlds until something happened long ago.
So imagine for one moment that intrepid human explorers found a semi arid life bearing world. Surface water is only at 12% concentrated in a single sea the size of the Mediterranean, fresh water lakes and hyper saline lakes surrounded by expansive salt-flats. The rest of the surface is taken up by sandy deserts, grassland like steppes, and trees only exist around fresh water oasis.
But everywhere the humans set up camp, everywhere the probes investigate, there is evidence of a completely different world. Fossils of alien fish and other aquatic creatures, the salt flats that were once sea beds, water carved landscapes where water hasn’t flowed in millions of years, and steep drop offs that were obviously once continental selfs.
All the evidence seems to be pointing to a single conclusion. Millions of years ago, there was a massive extinction level event in which somehow this once verdant planet lost most of its oceans and this dry arid world is still recovering from it.
So now everyone from the scientists on the expedition to the populace and politicians back home are all asking the same question.
What the hell happened to this planet?
What scientifically feasible scenario could happen that would cause a life supporting planet to dry up and loose it’s oceans?