This question has always been bugging me. Mars at some time in the past had enough liquid water on the surface to carve out gullies and riverbeds, and I would assume maybee even lakes or small oceans.



The most troublesom fact is that the atmosphere is so thin, water on the surface boils away into vapour despite cold temperatures. Like when high altitudes on earth become thin enough to lower water's vapour pressure at room temp.



It may currently be underground, which I have no problem accepting. I just want to know how it could have gotten there. A liquid past couldn't have been too distant, as in billions of years, given the amount erosion from wind and sandstorms.



I know next to nothing about the solar system, but nonetheless I like details so won't complain about too much info. Any response is appriceatied.

Earth is starting to do what mars did molten rock from the upper mantle is pushed up through the Earths crust



Each year they say about 112 billion tonnes of ocean water seeps into the mantles transition zone



The world oceans will dry up within a billion years



calculations on estimates of the volume of rock being subducted and the volume leaving the mantleand showing how much water is absorbed by the minerals primarily lawsonite formed in around about 100 kilometres below the surface



Geoscientists beliive that a huge reservor of water is bound up in minerals in the transition zone between the upper and lower mantles, about 400 kilometres below the Earth surface.



Water enters the mantle at subduction zones where oceanic crustal plates dive under continental plates. It returns to the surface at volcanic hot spots and mid-ocean ridges

Im not sure if thats what happend on mars



But liquid water on Mars is comming up from under the sand so maybe the oceans did leak mars dry

I studied from the oceans leaking water from the sources of



http://news.bbc.co.uk/1/hi/sci/tech/442040.stm

Does anyone else have any suggestions?



I'm extreamly skeptical of our oceans drying up in a billion years, but even if they will it dosn't answer the total question.



The other part of the question is how or why did liquid water on mars exist in sizable quantities without turning to vapour because of the low atmospheric pressure?



Do we have any evidence that the pressure was higher in the past?

What is the magnetic field of Mars?

;)