WCL (Wet Chemistry Lab) sample Options

[Juramike]

We'll soon know what kinds of crops we can grow on Mars! Bonus, the fruits will be already freeze-dried!

Handy list of preferred pH's of common garden plants.

-Mike

[siravan]

What does a pH of 8-9 do to the "missing carbonates" paradox? If there was liquid water on the surface of the Mars at some point of time and CO2 in the atmosphere, then pH 8-9 (in contrast to an acidic pH most of us expected) is ideal for precipitation of carbonates (e.g. limestone). Where are all those carbonates?

[dburt]

What does a pH of 8-9 do to the "missing carbonates" paradox? If there was liquid water on the surface of the Mars at some point of time and CO2 in the atmosphere, then pH 8-9 (in contrast to an acidic pH most of us expected) is ideal for precipitation of carbonates (e.g. limestone). Where are all those carbonates?

No one else has dared to tackle this, one of the biggest unanswered questions of Mars, so I'll foolishly try. One common hypothesis is that the ancient martian atmosphere was very different from today's, owing to a very high content of volcanic sulfur dioxide, itself caused by extremely active volcanism in the past. By this hypothesis, the acidification of surface waters by the atmosphere rendered deposition of carbonate rocks impossible. This would imply that the rate of absorption of acid species from the atmosphere always greatly exceeded the rate of neutralization of those acid species by the pulverized basic rocks of the martian crust. One chemical problem with this hypothesis is that seasonal or permanent ice cover on Mars would completely cut surface waters off from contact with the acidic atmosphere, allowing neutralization by reaction with rocks, at least seasonally. Another one is that surface waters on Earth (I know, terrestrial analogs are dangerous for Mars) are only rarely acidic, despite all the acids (carbonic, sulfuric, and nitric) constantly being tossed into the atmosphere by our civilization, not to mention our extremely active volcanism (compared to Mars). The implication is that surface rocks (on Earth at least) generally buffer the pH of surface waters to neutral or basic, even without an ice cover, and with active volcanism, coal-burning power plants, smelters, and so on.

Another common hypothesis, a far simpler one, is that, owing to low pressures and low temperatures, liquid water on Mars was always somewhat transient. That is, if present, it never stuck around long enough to reach chemical equilibrium with either surface rocks or the atmosphere, and thus to precipitate appreciable quantities of carbonates (other than the minor quantities found along fractures in some meteorites from Mars). Offhand, I'm not aware of any chemical problems associated with this hypothesis, but you may be. Also, keep in mind that the two hypotheses need not be mutually exclusive (that is, you could logically have a sulfur dioxide-rich ancient atmosphere, or any other ancient atmosphere, and transient or no liquid water at the same time).

Anyone else have any thoughts?

-- HDP Don