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According to this list mercury only makes up 6.7×10-6 % of the Earth's crust (by mass, I believe; though even if it's by number of atoms it's still tiny).

I'd like to make mercury sufficiently common on the surface of my world (relatively Earth-like, in the habitable zone, large liquid water oceans, feel free to assume anything else) so that the planet's ecosystem can (or rather has little choice but to) incorporate it into its biochemistry.

The percentage of the crust (by mass) that I am currently trying for (though if this is very implausible I am open to answers that aim for something more reasonable) is about 0.001%. Compared to Earth that's about 3 orders of magnitude more abundant.

I don't really mind in what form the mercury exists in, so long as it's fairly easy to extract pure elemental mercury out of it (cinnabar for example). However I would greatly appreciate answers that made it possible for pools/small puddles of quicksilver to form on the ground, even infrequently.

So my question is: what (natural) conditions could explain/permit a relatively Earth-like planet with high amounts of mercury in its crust?

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Do not overthink it

Every planet has its own chemical composition. Earth is not a be-all-and-end-all blueprint of how planets all throughout the universe must be.

If you feel you must throw in some kind of explanation (instead of just postulating that cinnabar is more prevalent) then simply assume that the star that created the heavy elements — "heavy elements" in this case is: everything other than hydrogen — that make up your planet, had a higher Metallicity before it went supernova(*) and spread its content around for new planets to form.

But all in all: do not overthink it. There is nothing that says Earth-like conditions is how things must be. You will not strain anyone's Willing Suspension of Disbelief if you just leave out the numbers and postulate that cinnabar is more prevalent than on present-day Earth.

As for puddles of mercury, no. Mercury will oxidize and form compounds, there is no way around that. Heating cinnabar is not enough for it to happen; you need to cool the vapours for pure mercury to form. If you tried — say for instance with volcanic activity providing the heat — yikes... you have just created a Planet of Death for any human-like creature if they try to breathe in that environment.

(*) Yes, every element in your body that is not hydrogen, was formed in the nuclear fusion furnace that is a star. That star then had to go supernova for those elements to be released and form planets. Stars had to die for you to live.

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    $\begingroup$ +1 for your footnote. "Stars had to die for you to live." Way to rock the cosmological parental guilt trip. $\endgroup$ – ShadoCat Oct 12 '17 at 17:26
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The natural abundance of mercury in the crust would be expected to vary due to natural variation in the composition of the materials that formed the planet. So you could easily have twice as much or even ten times as much just by chance.

But you may not need to have a much greater abundance of mercury in the crust to have more mercury available on the surface. If your planet is more geologically active than the Earth there would be more opportunity for wherever mercury was present to become concentrated into ores at or near the surface. As Mercury ores are believed to form from hydrothermal activity, what you need is more hydrothermal activity. This would be easier than trying to increase the abundance in the crust (but that would be a bonus).

Ore concentration processes are very efficient as they convert the trace 0.5mg/kg crust up to 5% or even 50%. You might find this of interest.

Mercury can occur in its elemental form, but this would normally be within the body of the ore itself which would protect it from oxidation. As metallic mercury does occur naturally, it is not inconceivable that it might pool under unusual circumstances. This is unlikely to be on the surface, but might occur underground in a cave for example, especially if it was sealed from the atmosphere. Needless to say it wouldn’t be a very healthy environment.

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  • $\begingroup$ You could mention changing the composition of the atmosphere to support elemental mercury, but +1 for the geological understanding of it $\endgroup$ – anon Oct 12 '17 at 15:14

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