Geological properties of lithium + Farming

[Sage_Rat]

I’m curious whether there might have used to have been a greater concentration of lithium in the top soil of farms (e.g. hundreds or thousands of years ago).

E.g. if we assume that the most common behavior of humans is to grow a plant in a valley, the plant will try to pull out any lithium from the top 6-12 inches of soil, the human will eat the plant and then throw their poop into a river then, given how lithium is distributed in the mantle and how it might replenish or deplete itself through the above process, erosion, etc. are we likely to have maintained historic levels or could there have been a change?

[CalMeacham]

I doubt it. I’ve worked with the alkali metals, and lithium is comparatively rare, and hard to come by. Even though it’s present in huge quantities in seawater, it’s not a major constituent of rocks:

According to the Handbook of Lithium and Natural Calcium , “Lithium is a comparatively rare element, although it is found in many rocks and some brines, but always in very low concentrations. There are a fairly large number of both lithium mineral and brine deposits but only comparatively few of them are of actual or potential commercial value. Many are very small, others are too low in grade.”[56]

So I doubt it was there in large quantities in the first place. Plants may have moved it around and oncentrated it, but they didn’t have a huge amount to work with

Lithium is easily absorbed by plants[68] and lithium concentration in plant tissue is typically around 1 ppm.[69] Some plant families bioaccumulate more lithium than others.[69] Dry weight lithium concentrations for members of the family Solanaceae (which includes potatoes and tomatoes), for instance, can be as high as 30 ppm while this can be as low as 0.05 ppb for corn grains.[68] Studies of lithium concentrations in mineral-rich soil give ranges between around 0.1 and 50−100 ppm, with some concentrations as high as 100−400 ppm, although it is unlikely that all of it is available for uptake by plants.[69] Lithium accumulation does not appear to affect the essential nutrient composition of plants.[69] Tolerance to lithium varies by plant species and typically parallels sodium tolerance; maize and Rhodes grass, for example, are highly tolerant to lithium injury while avocado and soybean are very sensitive.[69] Similarly, lithium at concentrations of 5 ppm reduces seed germination in some species (e.g. Asian rice and chickpea) but not in others (e.g. barley and wheat).[69]

On the other hand, there’s a lot of sodium and potassium in rocks, in the ocean, and in plants and animals.

Lithium

[Sage_Rat]

@CalMeacham

So I doubt it was there in large quantities in the first place. Plants may have moved it around and oncentrated it, but they didn’t have a huge amount to work with

If differences of a few ppm in nutrition can make a notable difference on human behavior, then slight variations could have significant results. By “depletion” I don’t mean taking it from 50% of soil to 0% of soil, I meant more like it started at 5ppm and now it’s 3ppm, which would be a drop of nearly 50% compared to the original, but still just a trace element, either way.

That said, your information about uptake by plant species could point to changes in dietary preferences having large effects. E.g. moving from a potato diet to a corn diet might significantly reduce dietary exposure.

[Stranger_On_A_Train]

Despite the stable isotopes of lithium being almost exclusively primordial nucleotides (produced by ‘Big Bang’ nucleosynthesis) the abundance of lithium is quite low (basically the second lowest of the first thirty-odd elements by atomic mass, just ahead of beryllium), and even lower than predicted by theory. It is also not uptaken and used in biological processes like salts of potassium, sodium, and phosphorous in plants so it will get washed out of soil and ultimately into the oceans or down into bedrock substrate, and is not frequently redeposited as a constituent of animal waste products. As @CalMeacham notes, lithium is quite rare in grades worth mining even though it is present in seawater and in fact we find rich deposits of lithium almost exclusively in desiccated seabeds where it is deposited by evaporation.

Stranger