Explain the lithosphere: geologic events and processes, how soils form and are classified, and how human activity alters the land

Learning goal: Describe the structure of the solid Earth and the geologic events and processes that shape its surface; trace how one geologic event, natural or human-caused, affects the atmosphere, hydrosphere and biosphere; describe how soil forms, how its horizons and texture are identified, and how soil information guides land-use decisions; and hypothesize the consequences of human impacts on the lithosphere such as surface mining, hydraulic fracturing and urbanization.

The lithosphere in the Earth system. The lithosphere is Earth's rigid outer shell: the crust plus the cool uppermost mantle, broken into tectonic plates that move over the weaker, slowly flowing rock beneath. Below the crust lies the mantle, mostly solid rock that convects over millions of years, and below that a liquid outer core and a solid inner core of iron and nickel. Environmental science does not need the interior in detail; it needs the consequence. Heat escaping from the interior drives plate motion, and plate motion drives the geologic events, earthquakes, volcanic eruptions and mountain building, that periodically reorganize the surface that the other spheres depend on. Ohio sits in the stable interior of the North American plate, far from plate boundaries, so its geologic events today are slow ones: weathering, erosion, stream deposition, the sinking of ground over old mines, and the occasional small earthquake.

Geologic events and processes. Processes run continuously; events are the bursts that stand out. Weathering breaks rock down in place, physically (frost wedging, root growth) or chemically (rainwater slightly acidified by carbon dioxide dissolving limestone). Erosion moves the pieces, by water, wind, ice or gravity, and deposition lays them down elsewhere. Mass wasting is the downslope movement of rock and soil under gravity, from imperceptible creep to landslides and mudflows; a saturated slope stripped of vegetation is the classic setting. The rock cycle connects these to the interior: sediment is buried and cemented into sedimentary rock, heat and pressure transform rock into metamorphic rock, melting and cooling produce igneous rock, and uplift brings all three back to the surface to be weathered again. Most of Ohio's bedrock is sedimentary, formed in ancient seas and swamps; the state's coal, limestone, shale, salt and sandstone are all resources of that history. The northern and western parts of the state were repeatedly covered by glaciers, which flattened the land and left thick deposits of till; the southeast was never glaciated and keeps its rugged hills and thin, easily eroded soils.

One event, four spheres: a worked model in the prose. Consider a large explosive volcanic eruption, of the kind that occurs in Iceland where a spreading plate boundary crosses the island. In 2010 an eruption there sent fine ash high into the troposphere and, because the jet stream carried it over Europe, aviation across much of the continent was halted for about a week. Trace the spheres. Lithosphere: new lava and ash deposits, and the collapse of part of the volcano. Atmosphere: ash and sulfur dioxide injected aloft; sulfur dioxide converts to sulfate droplets that reflect sunlight and, in very large eruptions, cool the planet slightly for a year or two. Hydrosphere: meltwater floods where the eruption occurred beneath a glacier, and ash that settles on rivers and lakes changes their chemistry and clarity. Biosphere: livestock and vegetation buried or poisoned by ash near the source, fish kills downstream, and, years later, unusually fertile soil where the ash weathers. Short-term impacts (the flights, the floods) and long-term ones (soil fertility, the new landform) come from the same event. A human-caused event, a pipeline rupture, for example, can be traced the same way: oil on the ground (lithosphere), volatile compounds evaporating (atmosphere), a sheen carried down a stream (hydrosphere), coated birds and smothered invertebrates (biosphere).

Soil. Soil is not simply dirt; it is a living mixture of weathered rock fragments, decomposed organic matter, water, air and organisms that forms so slowly that it should be treated as a nonrenewable resource on human time scales. A vertical cut through a mature soil shows horizons: the O horizon of leaf litter and humus at the top; the A horizon, or topsoil, dark with organic matter and the most biologically active layer; often an E horizon from which clay and minerals have been washed downward; the B horizon, or subsoil, where those materials accumulate; the C horizon of partly weathered parent material; and R, the unweathered bedrock. Texture is the proportion of sand (the coarsest particles), silt and clay (the finest). Texture controls how fast water drains, how much water and how many nutrients the soil holds, and how easily it erodes. Sandy soils drain fast and hold few nutrients; clay soils hold water and nutrients but drain poorly and compact; a loam balances them. A simple jar test estimates texture: shake a soil sample in water, and sand settles within about a minute, silt within a couple of hours, and clay takes a day or more. Reading the settled layers gives approximate proportions.

Using soil data for decisions. The United States Department of Agriculture publishes soil surveys that map soil types with their texture, drainage class, slope, depth to bedrock and suitability ratings for uses such as crops, septic systems and building foundations. Suppose a hypothetical tract for sale in an Ohio township is mapped as a poorly drained silty clay loam on a nearly level surface with a seasonal high water table close to the surface. The survey would rate it well for certain crops if artificially drained, poorly for basements and septic systems, and as a candidate for wetland restoration. A recommendation based on the data can say all three; a recommendation without the data is a guess.

Human impacts on the lithosphere. Surface mining removes the overlying rock and soil to reach coal or aggregate. Reclamation laws now require the land to be regraded and revegetated, but the reconstructed soil is compacted and lacks structure, and exposed sulfur-bearing minerals react with water and oxygen to produce acid mine drainage, the orange-stained, low-pH streams still found in parts of southeastern Ohio's old coal districts. Hydraulic fracturing injects water, sand and chemicals at high pressure to crack deep shale and release gas and oil; in eastern Ohio the target is the Utica shale. Possible consequences to hypothesize and then test against data: large water withdrawals, the handling and disposal of salty, chemically contaminated wastewater, methane leakage, and small earthquakes; in Ohio the best-known case, the 2011 earthquakes near Youngstown, was linked to a deep injection well used to dispose of that wastewater, while a smaller number of minor earthquakes, such as those in Poland Township in 2014, were linked to fracturing itself activating an existing fault. Urbanization replaces soil with pavement and roofs. Compaction and impervious surfaces stop infiltration, so rainfall runs off faster and carries sediment and pollutants; excavation and fill change slopes and trigger slumps; and the topsoil that took millennia to form is scraped away and sold or buried. Each of these is a hypothesis to test with measurements: stream pH below an old mine, seismograph records near injection wells, runoff volumes before and after paving.

What a layer model cannot show. A cutaway model of Earth's interior or a soil column shows structure at one moment. It cannot show rates: the slow convection that moves plates, the thousands of years to build a few centimeters of topsoil, or the minutes it takes a bulldozer to remove them. Rates, not structure, are what make soil a resource to conserve.

Worked jar test: A hypothetical school-ground sample shaken in a jar settles into three layers: sand 2.0 cm, silt 1.5 cm, clay 0.5 cm, total 4.0 cm. Sand: 2.0/4.0 = 50%. Silt: 1.5/4.0 = 37.5%. Clay: 0.5/4.0 = 12.5%. On the standard texture classification, roughly 50% sand, 38% silt and 12% clay is a loam. Conditions: the jar test measures settled thickness, not mass, and organic matter floats and is excluded, so this is an estimate; a laboratory analysis could differ by several percent.

Worked event trace: A hypothetical slope above a town, logged the previous year, receives 150 mm of rain in two days and fails as a mudflow. Lithosphere: several thousand cubic meters of soil and rock move downslope, and the slope is left steeper and bare. Hydrosphere: the flow dams the creek, forming a temporary lake, and sediment turns the river brown for weeks. Atmosphere: little direct effect; the cause ran the other way, from the atmosphere (the rain) to the lithosphere. Biosphere: forest and animals buried at the source; downstream, fish gills clogged by sediment and spawning gravel smothered. Short-term: the blocked road and turbid water. Long-term: the changed channel and the years before vegetation stabilizes the scar. Contributing human factor: logging removed the roots that bound the soil and the canopy that intercepted rain.

Worked land-use recommendation: A hypothetical 40-hectare tract is mapped as two soils: 30 hectares of well-drained silt loam on a 2% slope, and 10 hectares of very poorly drained muck along a stream. Recommendation with reasons: the silt loam is suitable for row crops, pasture or building with ordinary foundations, and its gentle slope limits erosion risk; the muck should be kept as wetland or buffer because it floods, will not support foundations without special engineering, and filters runoff before it reaches the stream. The data justify a split use; a single use for the whole tract would misuse one part.

Worked acid mine drainage reasoning: A hypothetical stream below an abandoned surface mine measures pH 3.5 and has orange coatings on its rocks; a similar stream in an unmined valley measures pH 7.2. Reasoning: mining exposed sulfur-bearing minerals such as pyrite in the spoil; oxygen and water react with them to form sulfuric acid and release dissolved iron, which lowers the pH and keeps the iron in solution; when the acidic water reaches the stream and mixes with oxygen, the iron precipitates as orange hydroxide. The comparison stream is the control; the difference points to the mine as the source, though a full investigation would sample at several points between the mine and the stream.

Representation task: Draw a labeled soil profile showing the O, A, E, B, C and R horizons with one sentence on what each contains. Beside it, draw a cross-section of a slope showing where a mudflow would start and stop, and annotate three factors that make failure more likely (steepness, saturation, vegetation removal). Then complete a four-row table for one geologic event of your choice with the short-term and long-term impact on each sphere.

Safe investigation, soil texture and drainage: Collect small samples of soil from two different spots (with permission; wash hands afterwards). For each, half-fill a clear jar, add water to near the top and a drop of dish soap, shake for two minutes and let it stand. Mark the sand layer after one minute, the silt layer after two hours and the clay layer after 24 hours; measure each thickness and calculate percentages. Separately, place equal volumes of each soil in identical funnels lined with filter paper, pour 100 mL of water through each, and time how long it takes for 50 mL to drain. Record everything. What the results support: a comparison of texture and drainage between the two samples. What they cannot show: nutrient content, organic matter, or how the soil behaves when compacted under a building.

Independent performance: Choose one human impact on the lithosphere (surface mining, hydraulic fracturing or urbanization) and write a report of at least 250 words that: states what the activity physically does to the lithosphere; hypothesizes three possible consequences for the other spheres; for each hypothesis, names one measurement that would test it and what result would support it; describes one existing remedy or regulation in general terms; and distinguishes clearly between what is established and what you are hypothesizing. Success criteria: every consequence is paired with a testable measurement, and no statistic is invented.