but we may be getting a little far afield from the apparent findings of methane and ammonia in the current Martian atmosphere.

Where do they come from, if they are there?

For the sake of discussion, let's accept the notion that Mars is pretty cold to significant depths, and that volcanic activity slowed to the point of pretty much inactivity long ago.

Assuming a cold surface and subsurface, and a near absence of volcanic activity, where do these highly reactive substances come from? How are they renewed?

Is Andrew's "pre-biology" sufficient? How would it function in a hostile, cold and almost inactive environment?

Cheers, BRFelix