Liquid Oxygen
Is it at all possible that liquid oxygen was present on mars? We think that mars had an atmosphere at one time and that it was due to the core being shut down perhaps by a core jolting asteroid that it lost the atmosphere.
If we suppose that it's core was extremely active and that that its volcanic activity was even more abundant then earth's, which created most of our oxygen, then perhaps the surface pressure exceeded 137.9 kPA and it was liquid oxygen that dominated the the Martian surface and not water. This could also account for the pebbles.
Has anyone ever explored this hypothesis?