Earth Science and Environmental Systems: Unit 4 Overview

These flashcards cover key concepts in Earth Science related to plate tectonics, soil formation, atmospheric layers, and climatic phenomena.

Plate Tectonics

The overarching scientific theory that describes the large-scale motion of Earth's lithosphere. It posits that the outer rigid layer of the Earth (the lithosphere) is broken into several large plates, known as tectonic plates, which are in constant slow motion relative to one another. These plates 'float' on the semi-fluid asthenosphere, driven primarily by mantle convection currents, ridge push, and slab pull. This theory explains many geological phenomena, including earthquakes, volcanoes, and mountain building.

Lithosphere

The rigid outermost shell of a terrestrial-type planet or natural satellite. On Earth, it is composed of the crust and the uppermost part of the mantle, extending to a depth of about 100\ \text{km} (62\ \text{miles}). It is fractured into large, moving tectonic plates.

Asthenosphere

A highly viscous, mechanically weak, and ductile region of the upper mantle of the Earth. It lies directly beneath the lithosphere, extending from about 100\ \text{km} to 700\ \text{km} (62\ \text{miles} to 435\ \text{miles}) in depth. The relative fluidity of the asthenosphere allows the tectonic plates of the lithosphere to move across it.

Mantle Convection Currents (Plate Tectonics)

The primary driving force behind plate tectonics. This process involves the slow creeping motion of Earth's solid silicate mantle due to convection, where heat from the Earth's core causes molten rock to rise, spread out beneath the lithosphere, cool, and then sink. This cyclical movement drags the overlying tectonic plates along, causing them to move.

Ridge Push

A proposed mechanism for plate tectonics where the excess height of the mid-ocean ridge (where new oceanic crust is formed) causes gravity to push the oceanic lithosphere away from the ridge and down the sloping asthenosphere. This outward 'push' contributes to plate movement.

Slab Pull

A major driving force of plate tectonics, referring to the force exerted by a cold, dense oceanic plate as it sinks into the mantle at a subduction zone. The weight of the descending slab pulls the rest of the plate along behind it, effectively 'pulling' the entire plate movement.

Divergent Boundary

A type of tectonic plate boundary where two plates are moving away from each other. This separation allows magma from the mantle to rise to the surface, creating new crustal material. This process is known as seafloor spreading and typically forms mid-ocean ridges in oceanic crust or rift valleys in continental crust. Volcanic activity, usually effusive, and shallow earthquakes are common.

Seafloor Spreading

The process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge. As magma rises from the mantle, it solidifies to form new basaltic ocean floor, pushing the older crust further apart. This continuous creation of new crust contributes to the expansion of ocean basins.

Mid-Ocean Ridge

An underwater mountain range, formed by plate tectonics at a divergent oceanic plate boundary. These ridges are sites of active seafloor spreading, where magma rises from the mantle to create new oceanic crust. They are characterized by a central rift valley, frequent shallow earthquakes, and volcanic activity, such as the Mid-Atlantic Ridge.

Rift Valley

A linear-shaped lowland formed by the rifting of a continental plate at a divergent boundary. As the continental crust pulls apart, it thins and fractures, creating a depression. These valleys often extend for hundreds of kilometers and can lead to the formation of new ocean basins over geological timescales, a famous example being the East African Rift Valley.

Convergent Boundary

A tectonic plate boundary where two plates move toward each other, resulting in a collision. The outcome depends on the types of crust involved (oceanic vs. continental) and their densities. This can lead to subduction (one plate sliding beneath another), uplift, volcanism, intense seismic activity, and the formation of deep ocean trenches, volcanic arcs, or mountain ranges.

Subduction Zone

A long, narrow zone where one tectonic plate is forced to sink beneath another plate at a convergent boundary. This typically occurs when a denser oceanic plate converges with a less dense continental plate or another oceanic plate. Subduction zones are characterized by deep oceanic trenches, intense seismic activity, and volcanism resulting from the melting of the descending slab within the mantle.

Oceanic Trench

A long, narrow, and deep depression in the ocean floor, typically formed at convergent plate boundaries where one oceanic plate subducts beneath another oceanic or continental plate. These are the deepest parts of the ocean, such as the Mariana Trench, and are associated with subduction zones and intense geological activity.

Volcanic Arc

A chain of volcanoes formed above a subducting plate, positioned in an arc shape as seen from above. These arcs are characteristic features of convergent boundaries, where magma generated from the partial melting of the subducting oceanic slab rises to the surface to form volcanoes. They can be island arcs (e.g., Japan) or continental volcanic arcs (e.g., the Andes).

Oceanic-Continental Convergence

A type of convergent plate boundary where an oceanic plate collides with a continental plate. Due to its greater density, the oceanic plate subducts beneath the continental plate, forming a subduction zone, a deep oceanic trench, and a chain of volcanoes along the edge of the continent (a continental volcanic arc), as seen in the Andes Mountains.

Oceanic-Oceanic Convergence

A type of convergent plate boundary where two oceanic plates collide. The denser of the two oceanic plates will subduct beneath the other, leading to the formation of a deep oceanic trench and a volcanic island arc parallel to the trench above the subducting slab, such as the Mariana Islands.

Continental-Continental Convergence

A type of convergent plate boundary where two continental plates collide. Because both continental plates are relatively buoyant and too light to subduct significantly, their collision results in massive compression, crumpling, and uplift of the crust, forming exceptionally high and extensive mountain ranges (orogens), such as the Himalayas.

Transform Boundary

A tectonic plate boundary where two plates slide horizontally past each other, usually along a transform fault. At these boundaries, crustal material is neither created nor destroyed. The friction between the plates causes stress to build up, which is periodically released as powerful earthquakes. A prominent example is the San Andreas Fault in California.

Fault (Geology)

A fracture or zone of fractures between two blocks of rock. Faults allow the blocks to move relative to each other, frequently as a result of crustal stress. This movement can be sudden, resulting in an earthquake, or gradual (creep). They are a key feature of transform plate boundaries but can occur in all tectonic settings.

Seismic Activity

Refers to the frequency, type, and size of earthquakes experienced over a period of time in a particular region. It is a direct manifestation of the stresses and movements within the Earth's lithosphere, particularly concentrated along plate boundaries where sudden slips along faults generate seismic waves.

Soil Formation

The complex, multi-stage process by which loose unconsolidated material (parent material) is transformed into soil through a combination of physical, chemical, and biological mechanisms. It involves the breakdown of rocks (weathering), the accumulation and decomposition of organic matter, and the vertical redistribution of materials within the soil profile. The five major factors influencing soil formation are climate, organisms, relief (topography), parent material, and time (often remembered by the acronym CLORPT).

CLORPT Factors

An acronym representing the five major interactive factors that control the formation of soil: Climate (temperature, precipitation influencing weathering and organic decomposition), Organisms (vegetation, microbial activity, fauna), Relief (topography, slope affecting erosion and drainage), Parent Material (the geological base rock or unconsolidated sediments), and Time (duration over which soil-forming processes have acted). These factors collectively determine the unique characteristics of a soil.

Parent Material

The underlying geological material from which soil is formed, serving as the raw mineral ingredient. It can be bedrock (igneous, sedimentary, metamorphic rock), or unconsolidated sediments like glacial till, alluvial deposits (river sediments), loess (wind-blown silt), or volcanic ash. The composition and texture of the parent material significantly influence the initial characteristics and nutrient content of the developing soil.

Humus

The stable, dark-colored organic matter that results from the decomposition of plant and animal residues by microorganisms in the soil. It is a vital component of fertile soil, improving soil structure, enhancing water retention and nutrient-holding capacity (cation exchange capacity), buffering soil pH, and providing a slow-release source of nutrients for plants over time.

O Horizon

The uppermost layer of soil, primarily composed of organic material at various stages of decomposition, with little to no mineral soil present. It is often subdivided into the Oi (undecomposed litter like leaves and twigs), Oe (partially decomposed organic matter), and O_a (highly decomposed, amorphous humus). This horizon is critical for nutrient cycling, infiltration, and providing habitat for soil organisms.

A Horizon (Topsoil)

Located directly beneath the O horizon (or at the surface if the O horizon is absent), this layer is characterized by an accumulation of humified organic matter intimately mixed with mineral soil. It is typically darker than underlying horizons, rich in nutrients, and exhibits significant biological activity. It is the primary layer for plant root growth and where topsoil management is crucial for agricultural productivity. This horizon is also subject to eluviation.

Eluviation

The process of removal (or 'washing out') of soil materials, such as clay, iron, aluminum oxides, and organic matter, from an upper soil horizon (typically the A or E horizon) by percolating water. These leached materials are then often deposited in a lower horizon, usually the B horizon.

E Horizon

A light-colored, often grayish, leached mineral horizon found below the A horizon and above the B horizon in some soil types, particularly in forested soils. It is characterized by eluviation, where clay, iron, aluminum oxides, and organic matter have been removed by downward-moving water, leaving behind a concentration of resistant sand and silt particles.

B Horizon (Subsoil)

Located beneath the A or E horizon, this layer is often characterized by the accumulation (illuviation) of materials leached from the overlying horizons. These accumulated materials can include clay, iron and aluminum oxides, and sometimes organic matter (typically less humified than in the A horizon). It generally has less organic content and biological activity than the A horizon but plays a crucial role in water storage and nutrient retention due to its higher clay content.

Illuviation

The process of accumulation (or 'washing in') of soil materials, such as clay particles, iron oxides, aluminum oxides, and humified organic matter, in a specific soil horizon (typically the B horizon) after they have been leached or moved from an overlying horizon by percolating water.

C Horizon

The layer of soil found beneath the B horizon, consisting of partially weathered or unweathered parent material. It contains minimal organic matter and shows little evidence of soil-forming processes like eluviation, illuviation, or biological activity. This layer serves as a transition zone between the developed soil above and the unweathered bedrock below. It can be made of unconsolidated sediments or fractured bedrock.

R Horizon (Bedrock)

The deepest layer in the soil profile, consisting of unweathered, consolidated rock (bedrock). It lies beneath the C horizon and is the source from which many soils ultimately form. This layer is impenetrable to roots and water, and it represents the solid geological foundation.

Weathering

The in-situ (on-site) process of breaking down rocks, soils, and minerals into smaller pieces or altering their chemical composition through contact with the Earth's atmosphere, biota, and waters. It does not involve the removal of the weathered material. Weathering is broadly categorized into two main types: physical (mechanical) weathering and chemical weathering.

Physical Weathering

The process by which rocks are broken down into smaller fragments without changing their chemical composition. Major mechanisms include: frost wedging (water freezing in cracks), abrasion (grinding by sediment in motion), exfoliation (peeling of rock layers due to pressure release), thermal expansion and contraction, and root wedging (plant roots growing into cracks). These processes increase the surface area of rocks, making them more susceptible to chemical weathering.

Frost Wedging

A form of physical weathering that occurs in cold climates when water seeps into cracks and fractures within rocks, freezes, and expands by about 9\%\ in volume. This expansion exerts pressure on the rock walls, widening the cracks. Repeated cycles of freezing and thawing can eventually pry apart rock sections, leading to rock disintegration.

Chemical Weathering

The process by which rocks are decomposed or dissolved due to chemical reactions between minerals and external agents like water, oxygen, and acids. This alters the mineral composition of the rock, forming new minerals or releasing ions into solutions. Common types include dissolution (e.g., limestone by carbonic acid), oxidation (e.g., iron-bearing minerals), hydrolysis (reaction with water), and carbonation (reaction with carbonic acid).

Oxidation (Weathering)

A type of chemical weathering where iron-bearing minerals in rocks react with oxygen in the presence of water to form iron oxides (rust). This process weakens the rock structure, often giving rocks a reddish-brown coloration and making them more susceptible to further physical and chemical breakdown.

Erosion

The process by which weathered rock and soil particles are transported from one location to another by natural agents. Unlike weathering, erosion involves movement. The primary agents of erosion are water (rivers, rain, ocean waves), wind, ice (glaciers), and gravity (mass wasting). Erosion plays a critical role in shaping Earth's landscapes.

Agents of Erosion

The natural forces responsible for the transportation of weathered rock and soil particles. The main agents include: \n- Water: Through rainfall, sheet wash, rivers, streams, and ocean waves. \n- Wind: Especially in arid and semi-arid regions, transporting fine particles like sand and dust. \n- Ice: Primarily through glaciers, which pluck away and abrade bedrock, carrying vast amounts of material. \n- Gravity: Leading to mass wasting events where material moves downslope under its own weight.

Mass Wasting

The downslope movement of rock, soil, and regolith under the direct influence of gravity. It is a critical component of the erosional process. Mass wasting events are classified based on the type of material, the nature of movement (e.g., fall, slide, flow), and the speed. Examples include rockfalls, landslides, mudflows, creeps, and slumps, often triggered by heavy rainfall, earthquakes, or wildfires in unstable slopes.

Permeability

A measure of the ability of soil (or any porous material) to transmit fluids (like water) and gases through its pore spaces. It is determined by the size and connectivity of the pores. Highly permeable soils (e.g., sandy soils) allow water to pass through quickly, while poorly permeable soils (e.g., clayey soils) restrict water movement. It influences drainage, aeration, and groundwater recharge rates.

Soil Texture

The relative proportions of the three primary mineral particles—sand, silt, and clay—in a given soil sample. Soil texture is a fundamental soil property that significantly influences water infiltration, retention, drainage, aeration, nutrient holding capacity, and workability. It is determined by the percentage by weight of each of these particle size fractions.

Sand (Soil)

The largest mineral particle size fraction in soil, typically ranging from 0.05\ \text{mm} to 2.0\ \text{mm} in diameter. Sand particles are coarse, irregular, and visible to the naked eye. Sandy soils are characterized by large pore spaces, leading to excellent drainage and aeration, but poor water retention and nutrient-holding capacity due to their low surface area and minimal charge.

Silt (Soil)

The medium-sized mineral particle fraction in soil, ranging from 0.002\ \text{mm} to 0.05\ \text{mm} in diameter. Silt particles feel smooth and powdery when dry, and somewhat slippery when wet, resembling flour. Silt-rich soils generally have good water retention and nutrient content, but can be prone to compaction and crusting.

Clay (Soil)

The smallest mineral particle size fraction in soil, with particles less than 0.002\ \text{mm} in diameter. Clay particles are microscopic, plate-like, and have a high surface area-to-volume ratio, often carrying a negative electrical charge. Clayey soils are characterized by small, numerous pore spaces, leading to high water retention, high nutrient-holding capacity (due to high cation exchange capacity), but poor drainage and aeration. They can be sticky when wet and hard when dry.

Loam (Soil)

An ideal soil texture classification that is a balanced mixture of sand, silt, and clay particles (typically around 40\%\ sand, 40\%\ silt, and 20\%\ clay). Loamy soils are considered optimal for agriculture because they exhibit a good balance of desirable properties: good drainage and aeration from sand, nutrient retention and water holding from silt and clay, and easy workability.

Soil pH

A measure of the acidity or basicity (alkalinity) of the soil, expressed on a scale from 0 to 14. A pH of 7 is neutral, below 7 is acidic, and above 7 is alkaline. Soil pH is a critical factor influencing the availability of essential plant nutrients, the activity of soil microorganisms, and the toxicity of certain elements. Most plants thrive in a slightly acidic to neutral range (pH 6.0-7.0).

Insolation

An acronym for INcoming SOLar radiATION, referring to the solar energy that reaches the Earth's surface per unit area over a given time. It is a fundamental energy input that drives Earth's climate and weather systems. The amount of insolation received at a particular location is influenced by factors such as the angle of the sun's rays (latitude and time of day), the length of daylight, and the amount of atmospheric absorption, scattering, and reflection (e.g., by clouds and aerosols).

Hadley Cell

A large-scale atmospheric circulation pattern that dominates the tropical and subtropical regions. It involves warm, moist air rising at the equator (forming the Intertropical Convergence Zone - ITCZ), flowing poleward in the upper troposphere, cooling and sinking around 30^ extrm{\circ} latitude (creating subtropical high-pressure zones and deserts), and then flowing back towards the equator as trade winds near the surface. This cell is responsible for the distribution of heat and moisture from the equator to 30^ extrm{\circ} N/S.

Intertropical Convergence Zone (ITCZ)

A narrow zone near the equator where the northeast and southeast trade winds converge, characterized by rising warm, moist air, intense solar heating, and frequent thunderstorms and heavy rainfall. It moves seasonally with the 'thermal equator' and is a crucial component of the Hadley Cell, playing a significant role in global rainfall distribution.

Subtropical Highs

Persistent belts of high atmospheric pressure located around 30^ extrm{\circ} latitude in both the Northern and Southern Hemispheres. These zones are characterized by sinking, dry air from the Hadley Cell, leading to clear skies, warm temperatures, and low precipitation. Most of the world's major deserts (e.g., Sahara, Arabian, Australian) are located within or adjacent to these subtropical high-pressure systems.

Rain Shadow Effect

A climatic phenomenon that results in an area of significantly reduced precipitation on the leeward (downwind) side of a mountain range, creating arid or semi-arid conditions. This occurs because as moist air is forced to rise over the windward side of the mountain (orographic lifting), it cools and condenses, causing precipitation. By the time the air descends on the leeward side, it has lost most of its moisture and warms adiabatically, leading to dry conditions.

Orographic Lifting

The process by which air masses are forced to rise over elevated terrestrial features, such as mountains. As the air rises, it expands and cools adiabatically. If the air cools below its dew point, moisture condenses to form clouds and often leads to precipitation on the windward side of the mountain, playing a key role in the rain shadow effect.

Adiabatic Heating/Cooling

A process of temperature change in a gas (like air) occurring without the transfer of heat into or out of the system. \n- Adiabatic Cooling: Occurs when air rises and expands due to lower atmospheric pressure, causing its temperature to decrease. This is crucial for cloud formation. \n- Adiabatic Heating: Occurs when air descends and is compressed by higher atmospheric pressure, causing its temperature to increase. This explains the dry, warm conditions on the leeward side of mountains (rain shadow).

El Niño

The warm phase of the El Niño-Southern Oscillation (ENSO), a periodic climate pattern characterized by an unusual warming of the ocean surface waters in the central and eastern tropical Pacific Ocean. This warming typically occurs every 2-7 years and lasts for several months to a year. El Niño significantly impacts global weather patterns, often leading to increased rainfall in some regions (e.g., Peru) and droughts in others (e.g., Indonesia, Australia), as well as changes in marine ecosystems.

Southern Oscillation

A large-scale seesaw in atmospheric pressure between the western and eastern tropical Pacific Ocean. It is the atmospheric component of ENSO. During El Niño, the atmospheric pressure tends to be higher than normal over the western Pacific and lower than normal over the eastern Pacific. During La Niña, this pattern reverses. Changes in the Southern Oscillation directly influence the strength and direction of the trade winds and the distribution of rainfall.

ENSO (El Niño-Southern Oscillation)

A large-scale climate phenomenon that represents the interaction between the atmosphere and the ocean in the tropical Pacific, resulting in a periodic fluctuation in sea surface temperature and the air pressure across the equatorial Pacific. It has two primary phases: El Niño (warm phase) and La Niña (cold phase), and a neutral phase. ENSO is the strongest interannual fluctuation of the climate system on Earth and has significant global climate impacts on precipitation, temperature, and extreme weather events.

La Niña

The cold phase of the El Niño-Southern Oscillation (ENSO), characterized by an anomalous cooling of the ocean surface waters in the central and eastern tropical Pacific Ocean. During La Niña, the trade winds are typically stronger than average, pushing warm surface water westward and allowing colder, nutrient-rich water to well up in the eastern Pacific. This leads to distinct global weather patterns, often bringing increased rainfall to Southeast Asia and Australia, and drier conditions to parts of the Americas.

Groundwater Filtration

The natural process by which soil and geological layers cleanse water as it percolates downward through the ground to become groundwater. This filtration occurs through several mechanisms: \n1. Physical Filtration: Larger particles (sediments, microorganisms) are trapped in tiny pore spaces. \n2. Adsorption: Dissolved chemicals and pollutants adhere to the surface of soil particles and organic matter. \n3. Biological Degradation: Microorganisms in the soil break down organic pollutants. This process is crucial for purifying water, replenishing aquifers with clean water, and maintaining water quality in natural systems.

Aquifer

A permeable body of rock or unconsolidated material (e.g., gravel, sand, silt) that is capable of yielding significant quantities of groundwater to wells or springs. Aquifers store and transmit groundwater, acting as natural underground reservoirs. They are a vital source of fresh water for human consumption, agriculture, and industry, and their recharge is dependent on effective groundwater filtration and infiltration.

Percolation

The process by which water moves downward through the pore spaces in soil or rock due to gravity and capillary action. It is a critical component of the water cycle, allowing surface water to infiltrate the ground, recharge groundwater supplies (aquifers), and undergo natural filtration as it passes through the various soil horizons. The rate of percolation is influenced by soil texture, structure, and permeability.