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A key part of terraforming a dead world is to make soil. Without soil, crops don't grow. In nature on Earth, transforming an igneous flow into rich soil takes millions of years. Mars has an advantage because it's pulverized by meteorite strikes and partially hydrated. However, growing a fertile soil will take time. When I was a kid I read a book called "Farmer in the Sky" by Robert A. Heinlein. It was about an immigrant to Ganymede starting a homestead. The character was shocked when he saw the plot of land he was assigned, it was nothing but bedrock; but a neighbour picked up a stone and licked it, then said "this is good land". The first thing they did was use dynamite to blow up large boulders, then a machine as large as a combine used an ultrasonic saw blade to cut the bedrock into pieces. Another machine had rakes of ultrasonic blades that cut the rocks into smaller rocks. He made multiple passes, each time spacing the blades closer together to cut the stones smaller. Once he was down to the size of gravel (or crushed rock) he set the blades shallower with each pass as he spaced the closer. That layered the stones, large ones deep and progressing to smaller ones close to the surface. It continued through sand all the way to rock flour on top. They imported soil concentrate from Earth, containing soil bacteria and worms. His neighbour brought over a welcoming gift: a truck load of kitchen scraps. The immigrant farmer thought it really strange that this guy would haul his kitchen garbage over, but he explained that you don't use the expensive imported concentrate straight. You mix the concentrate with rotting kitchen scraps to expand it to several times it's mass, then lay stripes on the field. The first crop he grew on that land was soil. This is an interesting story, but the details are a bit off. First, rotting kitchen scraps are used today; it's called compost, so that's Ok. But straight rock flour isn't the best soil; it doesn't give up it's nutrients too quickly. Rock flour is a technical term, and it is used as a source of micro-nutrients. It is literally rock ground to the consistency of flour. However, sand and gravel won't decompose into soil, at least not within a single person's lifetime. So you want to pulverize the ground bedrock to rock flour all the way down to the cut bedrock surface. Second, you want a more aggressive means of decomposing that rock flour into soil. Feldspar will dissolve in hydrochloric acid; quickly in strong hot acid, slowly in mild warm acid. In fact, this is the basis for my paper on smelting aluminum from feldspar. Bauxite is the result of a tropical rainforest leaching all the nutrients from soil, what's left is silica, alumina, and rust. Strong alkali is used to dissolve alumina and silica, rust is left behind. Then a gas that becomes acid when dissolved is added to neutralize the pH; the aluminum hydroxide precipitates but silica stays in solution. Aluminum hydroxide is then dried and heated with oxygen from the air to become alumina. My process is the reverse: strong acid dissolves silica and alumina but leaves rust, a gas that becomes alkali when dissolved is added to neutralize the pH; aluminum hydroxide precipitates but silica stays in solution. From there it's the same. It works great with feldspar high in aluminum, anorthite and bytownite, but feldspar low in aluminum tends to dissolve the calcium, sodium, and/or potassium as well as aluminum leaving silica on the granules. Silica from high aluminum feldspar dissolves, but silica from low aluminum feldspar forms quartz. Once a layer of quartz as thin as a soap bubble forms on a granule, it stops dissolving. Luckily, the predominant form of feldspar on the surface of Mars is bytownite. So, how can we use this to make soil?
Over just a few million years, flowing water will convert feldspar to clay. Which clay depends on which feldspar you start with:
Albite with iron becomes iron smectite
Microcline becomes illite
Illite weathers to become kaolinite Several of the intermediates are ions in solution. So the trick to decomposing feldspar into clay is to leave all the decomposed ions in one big soup. So we need a strong acid and something to make that acid, all in a pool of water. That means some sort of swamp. Growing sphagnum moss produces acid with pH in the range 3 to 4.5, a strong acid. So the ideal is a peat bog; sphagnum moss is growing peat.
Procedure: start by clear cutting all the trees. I know, environmentalists will cringe at this point, but the objective is to convert it to an entirely different ecozone: from boreal shield to prairie. Next scrape off all the soil and sift to remove rocks and stones. Sell tree trunks for lumber, chip trees branches and roots and chop weeds and bushes, but keep grass and twigs separate. Mix the soil with wood chips and chopped weeds, that's your rich soil starter. Next use dynamite to shatter any boulders, and road building techniques (more explosives) to level rock outcrops and rises. When it's roughly flat, use rock cutting equipment to cut a flat level floor. It doesn't have to be polished, rough to the touch is Ok, bumps a few millimetres high are acceptable but it does have to be relatively smooth. Cut the edges to form the sides of a bowl, this will make the entire township one giant flat bottom bowl to hold water. Cut it 2½ metres deep. Then take all the rocks you cut out of bedrock, together with all the blasted boulders, and all the rocks, stones and gravel you collected; crush all that to rock flour. Fill the bowl with that rock flour, using road building roller vehicles to compress it. It doesn't have to be tamped, just compressed. The top layer will be more rock flour mixed with the compost you kept: top soil mixed with wood chips and chopped weeds and bushes. Lay that mix loosely over the surface. Cover with the twigs and grass to keep the soil from blowing away. If you did it right you should have 2 metre depth of soil with bowl sides half a metre above the soil top. Do this where there's a near-by river or stream, flood the whole thing with water. There should be a couple inches of water above the soil. Seed with sphagnum moss; that creates a peat bog. When you lay the rock flour, also lay water pumps with hoses leading to distant parts of the bog. This creates water circulation; you want acid water moving through the rock flour, especially deep, right down to the bedrock floor. A simple intake is a slow sand filter. That is formed by cutting a sump pit in the rock bottom, place a submersible sump pump at the bottom with a water proof electrical cord leading out, cover the pump with a stainless steel wire mesh. Then cover in gravel or crushed rock. The wire mesh has to be small enough that the gravel or rocks won't go through. Then cover the gravel with sand, the gravel and sand are approximately 1 meter deep. The top of the sand should be level with the bedrock floor of the field. A slow sand filter 130cm diameter has a flow rate of 10 litres per minute. The output hose can lead to the surface elsewhere in the bog, the point is to create ground water movement throughout all the rock flour. The sand filter prevents the pump from getting clogged with rock flour, and prevents disturbing the growing peat. The pumps can be powered by solar panels. A water pipe or large diameter hose can bring water from the nearby stream. You don't want a lot of fresh water in the bog, it's supposed develop a strong acid, but you need to ensure it doesn't dry out. A simple device like the float in a toilet tank can control a pump to draw water from the stream, or if the stream inlet is up hill from the bog just a valve will do. Once the bog is covered in peat, no open water exposed, evaporation will dramatically slow; rain may be enough to replenish the bog.
"In summer, they can be found in small willow pastures and uplands where they feed on sedges, forbes and willows. In winter, they move to frozen wet sedge meadows and lakeshores where they feed on sedges. In the fall, they can be found in the forest where they feed on lichens." Wood Bison is the largest land animal in North America. It has red meat, almost indistinguishable from beef but more lean. I bought a pound of ground bison from a grocery store once, cooked into burgers. It tasted slightly better than lean ground beef. I believe it was Plains Bison. Oh, the common American term for Bison is Buffalo. It may take a while to build an oxygen atmosphere on Mars, but a peat bog can grow with very little atmospheric oxygen. Once there is an oxygen atmosphere, we can ranch Bison. I don't know how deep Mars soil is, but this procedure will create arable soil from even hard exposed bedrock. The above gives some grand ideas without numbers. Numbers for dissolving feldspar in acid can be found in the paper Experimental study of anorthite dissolution and the relative mechanism of feldspar hydrolysis by ERIC H. OELKERS and JACQUES SCHOTT, published in Geochimica et Cosmochimica Acta, Vol. 59, No. 24, pp. 5039-5053, 1995. Table 5 on page 5048 of this paper lists dissolution rates for various pH and temperature. At 25°C and 3.5 pH you get -12.57 expressed as a logarithm in mol/cm2/sec. That means 1/1012.57 moles per square centimetre per second. Rock flour has a particle size such that 75% passes through a mesh of 0.075mm or larger. Solid basalt has a density of 3011 kg/m3, the particle size has a volume 0.00022 cubic millimetres or 0.22×10-12 cubic metres. Therefore each particle mass is 665×10-12 kg or 665×10-9 grams. Anorthite has a chemical formula of CaAl2Si2O8 which has a molecular weight of 278.2072772 grams per mole. That means 2.39×10-9 moles. Assuming spherical particles (they won't be that neat), the surface area is 0.0001767cm2. That means 50,267,598 seconds, or 581.8 days. So a little under 2 years if you maintain temperature at +25°C and pH at 3.5. It won't be that neat, so a few years. As an example, Bissett has mean daily temperature between 11°C and 19°C for May through September. The Mean for April and October is +3°C and +4°C respectively. Extrapolating for +15°C produces a dissolution rate of -12.68 as a logarithm in mol/cm2/sec. That will take 749.5 days. There are 153 days in those months, so it will take 4.8987 years; round it off to 5 years. It may take one year for sphagnum moss to grow to cover the area and produce strong acid, and a summer season before that to clear-cut the land and grind bedrock into rock flour, so 7 years from setting foot on the land to completion. Once complete, acidity within the soil will have to be neutralized. The Boreal Forest Research Centre lists wood ash as an effective means to neutralize acidic soil. That can either be purchased, or if trees were grown in the bog they can be burned. Soil pH lower than 5.1 is considered very acidic and infertile. The 3.0-3.5 pH of a peat bog is well below that. Fine textured Black soil, organic, and peaty soils require 3-4 tonnes/acre wood ash to raise pH by one point. To raise soil from 3.5 to 5.5 is two whole pH points. The way pH works, it takes 10 times as much ash to raise 2 points as it does one. That means 30 to 40 tonnes per acre, assuming soil is pH 3.5 after draining. Moderately acidic soil is pH 5.5 to 5.6, so this treatment is minimum. Growing trees in the bog may be an economic necessity. On Mars it will, transporting ash from Earth is way too expensive. |
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