re: Mars Express and the Omega spectrometer
As a quick summary, the first "age" of Mars, from 4.6 to 4.0 Ga was moist and most suitable for life (but this was also the time before the great impact basins were formed). From 4.0 to 3.5 Mars became more sulphurous and acidic due to extended volcanic activity, and since 3.5 G1 it gas remained dry and dusty.
I can live with this as a history of the red planet...