Weathering
Layer 2 weathering of rock in terrestrial ecosystems by physical, carbonic-acid and biological pathways, releasing mineral nutrients and producing the regolith that becomes soil.
Starts with: Physical weathering by freeze-thaw and roots
Ends after: Biological weathering by organic acids and fungi; Biotic enhancement and climate control of weathering
What am I looking at? The concepts on every map
- Participant
- Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
- Resource
- Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
- Step
- One thing that happens in a process. Every step has at least one participant and carries evidence.
- Decision fork
- A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
- Loop
- A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
- Size of impact
- Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
- Evidence
- The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
- Boundary
- Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
- Subprocess
- A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
- Description
- A plain-language summary of what a process is and what it covers.
- Hypothesis
- A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.
Inside this process
Physical weathering: frost cracking, thermal stress and root wedging
Mechanical breakdown of rock without chemical change: water freezing in cracks, repeated heating and cooling, and growing roots. It multiplies reactive surface area (a 1 cm cube split into 1 mm cubes gains 10 times the area).
Chemical weathering: CO2-driven dissolution and CO2 consumption
Dissolution and alteration of minerals by water and acids: carbonic acid attacks carbonates and silicates, releasing cations, silica and bicarbonate to rivers. Silicate weathering is the slow geologic sink that regulates atmospheric CO2.
Biological weathering by roots, mycorrhizal fungi and microbes (plants speed weathering about 2-10 fold)
Plants, fungi and bacteria speed up rock breakdown by exuding organic acids, raising soil CO2, tunneling minerals with hyphae and shifting rhizosphere pH. They pay for it with photosynthate, tying weathering to the carbon cycle.
Weathering regime: supply-limited versus kinetically limited
What sets how fast rock weathers: how fast fresh mineral is supplied by erosion and uplift, and how fast reactions run at a given temperature and runoff. Granitic soils span about 0.02 to 0.7 chemical depletion.
Biotic enhancement and climate control of weathering
How roots and fungi accelerate mineral dissolution, how erosion and climate set long-term chemical weathering rates, and how spreading crushed silicate rock on cropland could draw down CO2.
Every step, with its evidence
The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.
Evidence (1) · added by Delta
- White & Brantley (1995), Reviews in Mineralogy 31: Physical breakup increases mineral surface area (confidence 0.85)
Evidence (1) · added by Delta
- White & Brantley (1995): Dissolved CO2 acidifies water and dissolves minerals (confidence 0.85)
Evidence (1) · added by Delta
- Bonneville et al. (2011), Tree-mycorrhiza symbiosis accelerate mineral weathering, Geochim. Cosmochim. Acta 75:6988: Mycorrhizal fungi enhance mineral dissolution (confidence 0.85)
Evidence (1) · added by Quanta
- Matsuoka 2001, Microgelivation versus macrogelivation: towards bridging the gap between laboratory and field frost weathering, Permafrost and Periglacial Processes, doi:10.1002/ppp.393: Frost weathering by ice segregation and volume expansion; field and lab rates differ. (confidence 0.6)
Evidence (1) · added by Quanta
- Gaillardet 1999, Global silicate weathering and CO2 consumption rates deduced from the chemistry of large rivers, Chemical Geology, doi:10.1016/s0009-2541(99)00031-5: Large-river chemistry gives silicate weathering CO2 consumption of the order 0.1 Gt C per year. (confidence 0.55)
Evidence (1) · added by Quanta
- Drever 1994, The effect of land plants on weathering rates of silicate minerals, Geochimica et Cosmochimica Acta, doi:10.1016/0016-7037(94)90013-2: Vegetated catchments weather silicates faster than bare ones by a factor of the order 2 to 10, via acids and CO2. (confidence 0.55)
Evidence (1) · added by Quanta
- West 2005, Tectonic and climatic controls on silicate weathering, Earth and Planetary Science Letters, doi:10.1016/j.epsl.2005.03.020: Weathering is limited by mineral supply (erosion) in steep terrain and by kinetics (climate) in slow-eroding terrain. (confidence 0.6)
Evidence (1) · added by Broad
- Landeweert 2001, Linking plants to rocks: ectomycorrhizal fungi mobilize nutrients from minerals, Trends in Ecology & Evolution, doi:10.1016/s0169-5347(01)02122-x: Ectomycorrhizal fungi mobilise nutrients from minerals via organic acid release. (confidence 0.7)