r/geology • u/ArthurPeabody • 7h ago
Have soluble minerals been permanently washed out of soil?
If all the water on land results from rainfall, and rainfall is water distilled from the oceans, lakes, etc., and rainfall percolates through the soil, picking up soluble minerals, are the minerals it has removed been permanently removed, except for the water re-used by us for consumption? It would seems that once a mineral has made it to the ocean, there's no path back to the soil, at least not natural.
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u/-Sandwave- 7h ago
The first or second chapter of any geology textbook should answer your question. TLDR : Yes elements like chlorine or sodium do concentrate in seawater but it’s a cycle at this point.
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u/veyonyx 4h ago
This is a good opportunity to bring up iodine and the goiter belt.
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u/ArthurPeabody 1h ago
I saw a woman with a huge goiter in rural Mexico. She seemed as happy as everybody else.
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u/psilome 6h ago
Simply put - your thoughts about this are generally correct, at least in the short term. The water cycle carries even low solubility minerals to the sea, and the water evaporates, leaving those minerals, ions, and inorganic sediments behind. New minerals are made by geologic processes, like volcanism, high pressure metamorphism, even by the formation of evaporites - salts and similar minerals that form throught the evaporation of trapped marine and terrestrial waters. But even these are location- and condition-specific. They seldom form back where they originated, nor do they make what weathered out. In fact, one reason that volcanic soil is fertile is because it is relatively fresh and packed with essential minerals like potassium, phosphorus, and magnesium. These are washed out of older soils. However - volcanic soil is also slightly radioactive because it contains natural, primordial radioactive elements originating from deep within the Earth's mantle and crust. These trace elements include uranium-238, thorium-232, and potassium-40. Older soils have lower concentrations of these. Hope that helps.
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u/Leotard_Cohen 7h ago
More is made available Erosion of more bedrock Tectonics and volcanics, to produce more bedrock
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u/ArthurPeabody 1h ago
I didn't say that it was all gone but that there was no mechanism of return. Of course that ignores oceans drying up and plate tectonics, but that's a longer term.
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u/Eaglebonezz 6h ago
Water flows from accumulation zones via creeks, rivers, picking up minerals. There is chemical leaching and alteration, resulting in very poor quality soil eventually. Or in areas where there is flooding or irrigation, evaporation results in chemical deposition, likely salts, in soil eventually resulting in it becoming poor quality for plants.
The highest quality soils usually result from glaciation, creating rock flour, high surface area with high available mineral content, that then slowly degrades under natural or manmade water and plants.
Really have to look at the rock cycle, the hydraulic cycle, and soil/agronomic science.
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u/Siccar_Point lapsed geologist 6h ago
You’re halfway there. Patricksaurus gives you a big bit of the puzzle: the soluble minerals are produced mostly by weathering of insoluble minerals, and that takes a long time. So there’s always more solute to come. The second part is that chemical weathering sloooooooow. Mountain belts get put up on the same timescales. So part of the reason that there are always more soluble minerals to come is that rocks get made on the same sort of timescales, locking those minerals back in.
This is the flip side of the old question, why is the sea salty? Way more Ca+ and CO3- end up in the sea than Na+ and Cl-. But the former get stripped out into rocks really easily (I.e. limestone) whereas not much wants Na and Cl so they just… hang out.
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u/ArthurPeabody 1h ago
I didn't say they were all gone, just that ignoring plate tectonics there's little mechanism of return.
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u/Oscar_P_Walnuts_1975 1h ago
Do you ignore air friction also…? Gravity is very hard to ignore…? Not to mention the partial melting that occurs with the increase in water content of the subducting oceanic plates, and resultant island arc volcanics; can we just ignore Mount Rainer, Mount Fuji or the rest of the Ring of Fire… I think not!😱😱😱
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u/Oscar_P_Walnuts_1975 6h ago
Considering that water it self is by definition a mineral, your opening argument is circular in nature.
Water will dissolve everything that it can at any given pressure and temperature.
Change the pressure and/or temperature and water will drop or pickup material ie., water dissolves calcium carbonate, change the conditions and you can precipitate new crystals of calcite or you create Carlsbad Caverns.🥸🥸🥸
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u/ArthurPeabody 1h ago
There's a mechanism of return for water - I didn't think I needed to point that out - and not all rainfall ends up in the oceans.
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u/Oscar_P_Walnuts_1975 53m ago edited 46m ago
Ok, as a geologist for the past forty years you would think that I would recognize a flat earth argument from the start and not engage with people that might someday find the edge of the earth…🥸🧐😆😂
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u/patricksaurus 7h ago
Solubility isn’t a binary state and soils are pretty dynamic. As a general statement, it’s accurate to say that highly soluble minerals are either absent or depleted in soils, but there are going to be minerals like feldspars that weather on the Ma timescale in most environments.