Unit 4 Beta

Earth Systems and Resources: the one-page sheet

4.1 Plate Tectonics

Convection in the mantle moves Earth's plates. Where plates spread apart (divergent), new crust forms; where they collide (convergent), a dense ocean plate sinks, making trenches, earthquakes and volcanoes, or continents crumple into mountains; where they slide past each other (transform), earthquakes strike. Hot spots build volcanic chains in the middle of plates. Knowing the boundary tells you the hazards a place faces.

Earth's outer layer is broken into rigid tectonic plates that ride on the hotter, slowly flowing mantle, moved by convection currents.
Divergent boundary: plates move apart; magma forms new crust (mid-ocean ridges, rift valleys, seafloor spreading).
Convergent boundary: plates move together. Ocean meets plate: the denser ocean plate sinks (subduction), making a trench, earthquakes and volcanoes. Continent meets continent: crust crumples into high mountains.
Transform boundary: plates slide past each other; earthquakes, little volcanic activity (the San Andreas Fault).
A hot spot is a fixed plume of magma under a plate; the plate moving over it leaves a chain of volcanoes that get older in one direction (Hawaii).

slow convection currents form in the mantle plates move a few centimeters a year, apart, together or past each other magma rises and forms new crust: mid-ocean ridges and rift valleys a trench, strong earthquakes and a chain of volcanoes form earthquakes shake the land, and a slip under the sea can launch a tsunami

convection: A loop of motion in a fluid heated from below: warm, less dense material rises, spreads, cools and sinks. Convection currents in Earth's mantle move the tectonic plates.
plate tectonics: The theory that Earth's rigid outer layer is broken into large plates that move slowly over the hotter mantle, driven by heat from inside Earth.
convergent boundary: A plate boundary where two plates move toward each other. A denser ocean plate sinks under the other plate (subduction), forming a trench, earthquakes and volcanoes; two continents crumple into high mountains.
divergent boundary: A plate boundary where two plates move apart. Magma rises and forms new crust, building mid-ocean ridges (seafloor spreading) or rift valleys on land.
transform boundary: A plate boundary where two plates slide past each other sideways. Stress builds and is released as earthquakes; there is little volcanic activity.
hot spot: A place where a column of hot mantle rock stays fixed while a plate moves over it, building a chain of volcanoes that get older in the direction the plate moves, such as the Hawaiian Islands.

4.2 Soil Formation and Erosion

Soil forms slowly from weathered parent material and humus from decomposed organisms, and it sorts into horizons: O, A (topsoil), B (subsoil), C and bedrock. Warm, wet climates form soil fastest. Wind and water erode soil, fastest where plants are removed and the ground is bare, and eroded soil harms both the land it leaves and the streams it reaches.

Soil forms from parent material (bedrock, or sediment carried by rivers, glaciers or wind) broken down by weathering, plus humus from decomposed organisms.
Climate, organisms, the shape of the land, the parent material and time control how fast soil forms. Warm, wet places weather rock and decompose matter fastest.
A soil profile has layers called horizons: O (organic matter), A (topsoil: humus and minerals), B (subsoil: minerals leached from above), C (partly weathered parent material), then bedrock.
Erosion is the removal and transport of soil by wind and water. Plant roots hold soil and plant cover shields it, so bare soil erodes fastest.
Eroded soil fills streams with sediment, carries nutrients and pesticides with it, and leaves farms with poorer subsoil.

the mineral part of soil forms humus forms and is mixed into the top of the soil the soil sorts itself into horizons: O, A, B, C wind and water carry topsoil away, far faster than new soil forms

parent material: The rock or sediment a soil forms from: the bedrock under it, or material carried in by rivers, glaciers or wind. It sets which minerals the soil starts with.
humus: Dark, crumbly organic matter in soil, left when decomposers break down dead plants and animals. It holds water and slowly releases nutrients.
soil horizon: One of the layers in a soil profile: O (organic matter), A (topsoil, humus mixed with minerals), B (subsoil, where leached minerals collect), C (partly weathered parent material), then bedrock.
erosion: The removal and transport of soil or rock by wind, water or ice. It speeds up where plants are removed and the ground is left bare.

4.3 Soil Composition and Properties

Soil texture, the share of sand, silt and clay, sets how soil behaves. Sand drains fast (high permeability) but holds little water or nutrients; clay holds water and nutrients but drains slowly; loam balances the two. The texture triangle reads a sample's class from its three percentages. Humus and a pH near 6 to 7 make soil more fertile.

Soil texture is the share of sand (largest), silt and clay (smallest) particles. The soil texture triangle turns the three percentages into a texture class.
Loam is a balanced mix (roughly 40% sand, 40% silt, 20% clay) that drains well yet holds water and nutrients.
Porosity is the share of soil volume that is pore space. Permeability is how easily water flows through: highest in sand, with large connected pores; lowest in clay, with tiny pores.
Water-holding capacity is how much water a soil can hold against gravity: highest in clay and soils rich in humus, lowest in sand.
Soil fertility is the soil's ability to supply nutrients. Clay and humus hold nutrients; pH controls whether roots can take them up (most crops prefer about 6 to 7).

sand leaves large pores, clay leaves very many tiny pores sandy soil has high permeability and drains fast clay soil has high water-holding capacity but drains slowly and can lack air a loam with humus is fertile, holds water and still drains

soil texture: The percentages of sand, silt and clay particles in a soil. The soil texture triangle turns the three percentages into a named texture class, such as loam or clay.
loam: A soil with a balanced mix of sand, silt and clay (roughly 40%, 40% and 20%). It drains well yet holds enough water and nutrients for most plants.
porosity: The share of a soil's volume that is pore space, the gaps between particles. Clay often has as much or more pore space than sand, but its pores are tiny.
permeability: How easily water flows through soil or rock. It depends on how large and well connected the pores are: high in sand, low in clay.
water-holding capacity: How much water a soil can hold after gravity drains the rest. It is highest in clay and soils rich in humus and lowest in sand.
soil fertility: A soil's ability to supply the nutrients plants need. Clay and humus hold nutrients against leaching, and a pH near 6 to 7 keeps them available to roots.
pH: A scale from 0 to 14 that measures how acidic or basic a solution is: 7 is neutral, below 7 is acidic, above 7 is basic, and each step is a tenfold change.

4.4 Earth's Atmosphere

The atmosphere is about 78% nitrogen and 21% oxygen, layered by how temperature changes with height. The troposphere, heated from the ground, cools upward and holds the weather. The stratosphere warms upward because its ozone layer absorbs ultraviolet light, shielding life below. The mesosphere cools upward again, and the thin thermosphere heats sharply.

Dry air is about 78% nitrogen, 21% oxygen and 0.9% argon; carbon dioxide is about 0.04%. Water vapor varies from about 0% to 4%.
The layers are defined by how temperature changes with height: the troposphere cools upward, the stratosphere warms upward, the mesosphere cools upward, the thermosphere warms upward.
The troposphere (ground to about 10-16 km, highest over the equator) holds about 75% of the air's mass and nearly all the weather.
The ozone layer, about 15 to 35 km up in the stratosphere, absorbs most of the Sun's ultraviolet (UV) radiation, which causes skin cancer and cataracts and harms plants and plankton.
Air gets thinner with height: about half of the air's mass is below 5.5 km.

the troposphere is warmest at the bottom and cools with height water vapor condenses into clouds, and weather forms in the troposphere the stratosphere warms with height, and most harmful UV never reaches the surface rising air stops near the top of the troposphere, so weather stays below about 10 to 16 km

troposphere: The lowest layer of the atmosphere, from the ground to about 10-16 km. It is heated from below, cools with height (about 6.5 °C per km), holds about 75% of the air's mass and nearly all weather.
stratosphere: The layer above the troposphere, to about 50 km. It contains the ozone layer, which absorbs ultraviolet light, so temperature rises with height.
mesosphere: The mesosphere (about 50 to 85 km), where temperature falls with height to the coldest air in the atmosphere, and the thermosphere above it, very thin air heated sharply by the Sun. Its outer edge is the exosphere.
ozone: A molecule of three oxygen atoms (O3). In the stratosphere it absorbs ultraviolet light; near the ground it is a pollutant that harms lungs and plants.
ozone layer: The region of the stratosphere, about 15 to 35 km up, where most of the atmosphere's ozone is found. It absorbs most of the Sun's harmful ultraviolet radiation.
ultraviolet radiation: Ultraviolet (UV) light: high-energy light from the Sun, shorter in wavelength than visible light. UV-B and UV-C damage DNA, causing skin cancer and cataracts and harming plants and plankton.

4.5 Global Wind Patterns

The Sun heats the equator most, so air rises there, drops its rain, travels poleward high up and sinks near 30°, forming the Hadley cell; Ferrel and polar cells lie beyond it. Rising air brings rain and sinking air brings dry weather. Earth's rotation, the Coriolis effect, bends the surface winds into the trade winds, the westerlies and the polar easterlies.

Uneven heating makes air rise near the equator and near 60° (wet) and sink near 30° and the poles (dry). The loops are circulation cells: the Hadley cell (0-30°), the Ferrel cell (30-60°) and the polar cell (60-90°).
The Coriolis effect: Earth's rotation deflects moving air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
Surface winds: the trade winds (0-30°) blow from the east toward the equator; the westerlies (30-60°) blow from the west; the polar easterlies (60-90°) blow from the east.
Winds are named for where they come from: a westerly blows from the west toward the east.
Global winds move heat from the tropics toward the poles and set where rain falls, so they help place biomes: rainforests near the equator, deserts near 30°.

warm air rises at the equator, cools and drops heavy rain sinking air warms, so the 30° latitudes are dry and hold many deserts steady surface winds form between the equator and 30° winds curve into the trade winds, the westerlies and the polar easterlies

Hadley cell: Large loops of rising and sinking air in each hemisphere: the Hadley cell (equator to about 30°), the Ferrel cell (about 30° to 60°) and the polar cell (about 60° to the pole). Air rises near the equator and 60° (wet) and sinks near 30° and the poles (dry).
Coriolis effect: The deflection of moving air or water caused by Earth's rotation: to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
trade winds: The steady surface winds of each latitude band: the trade winds (0° to 30°, from the east toward the equator), the westerlies (30° to 60°, from the west) and the polar easterlies (60° to 90°, from the east).

4.6 Watersheds

A watershed is all the land that drains into one stream, river or lake, bounded by high ground called a divide. Its slope, soil, plant cover and land use control how much rain runs off and how much soil and pollution reach the water. A watershed is surface land; an aquifer is water stored underground. Whatever happens anywhere in a watershed flows downstream.

A watershed (drainage basin) is all the land that drains into one body of water. High ground called a divide separates one watershed from the next.
Small watersheds nest inside larger ones: a creek's watershed is part of a river's, which is part of a larger basin.
Its area, slope, soil, vegetation and land use shape how much rain runs off, how fast, and how much soil and pollution the water carries.
A watershed is land that drains to surface water; an aquifer is water stored underground in rock and sediment. Water soaking in across a watershed can recharge an aquifer.
Protecting a stream means protecting its whole watershed, because water from all of it ends up there.

it runs downhill toward the same stream, river or lake, or soaks in more water runs off, faster, carrying soil and pollutants with it what enters anywhere upstream can reach every community downstream floods are smaller, streams are cleaner and aquifers are recharged

watershed: All the land that drains into one stream, river or lake, also called a drainage basin. High ground called a divide separates one watershed from the next. It is surface land, not underground water (an aquifer).

4.7 Solar Radiation and Earth's Seasons

Insolation, the solar energy per square meter, is highest near the equator because sunlight strikes it most directly. Earth's axis is tilted about 23.5°, so as Earth orbits, each hemisphere takes turns leaning toward the Sun: that tilt, not distance, makes the seasons. Albedo, the share of sunlight a surface reflects, decides how much of that energy the surface absorbs.

Insolation is the solar radiation reaching an area, in watts per square meter (W/m²). It is greatest near the equator, where sunlight is most direct.
Seasons come from axial tilt (about 23.5°): the hemisphere tilted toward the Sun has higher sun angles and longer days. Distance from the Sun is not the cause; Earth is closest in early January.
Northern summer is southern winter, and the reverse. Near the equator, insolation stays high all year, so seasons are mostly wet and dry, not warm and cold.
Albedo is the share of sunlight a surface reflects: high for snow and ice, low for ocean and forest. Low-albedo surfaces absorb more energy and warm more.
Insolation sets temperature by latitude, which helps place the biomes and drives the global winds.

insolation, the solar energy per square meter, is highest near the equator each hemisphere leans toward the Sun for half the year and away for the other half it has summer, while the other hemisphere has winter dark ocean and forest warm more than snow and ice under the same sun

insolation: Incoming solar radiation: the Sun's energy reaching an area, in watts per square meter (W/m²). It is greatest where sunlight strikes most directly, near the equator.
axial tilt: The tilt of Earth's axis, about 23.5°, which keeps pointing the same way as Earth orbits the Sun. It causes the seasons: the hemisphere tilted toward the Sun has summer.
albedo: The share of incoming sunlight a surface reflects. Snow and ice have a high albedo; open ocean and forest have a low albedo and absorb more energy.

4.8 Earth's Geography and Climate

Geography reshapes climate. Mountains force moist air up, so the windward side is wet and the leeward side is a dry rain shadow. Oceans heat and cool slowly, giving coasts milder climates than inland areas. Wind-driven ocean currents carry heat: warm currents warm nearby coasts, cold currents cool them. Higher elevations are colder.

Climate depends on latitude, but also on geography: mountains, nearness to the ocean, ocean currents and elevation.
Rain shadow: the windward side of a mountain range is wet; the leeward side is dry, because the air lost its moisture on the way up and warms as it sinks.
Water heats and cools more slowly than land, so coastal climates are milder (cooler summers, warmer winters) than inland climates at the same latitude.
Ocean currents, driven mainly by prevailing winds and turned by the Coriolis effect and the continents, form large loops called gyres. Warm currents (the Gulf Stream) warm nearby coasts; cold currents (the California Current) cool them.
Higher elevation means colder air, about 6.5 °C cooler per kilometer of height.

the air rises up the windward slope, expands and cools clouds form and heavy rain or snow falls on the windward side the leeward side is a dry rain shadow, often a desert ocean currents carry warm water toward the poles and cold water toward the equator, warming or cooling nearby coasts

rain shadow: A dry region on the leeward side of a mountain range. Moist air drops its rain as it rises and cools on the windward side, then sinks and warms on the leeward side, bringing little precipitation.
ocean current: A steady flow of ocean water, driven at the surface mainly by prevailing winds and turned by the Coriolis effect and the continents into large loops called gyres. Warm currents warm nearby coasts; cold currents cool them.

4.9 El Niño and La Niña

Normally the trade winds push warm water west across the Pacific, and cold, nutrient-rich water upwells off South America. In El Niño the trade winds weaken, warm water spreads east, upwelling weakens, fisheries off Peru decline and the rain shifts east. In La Niña the trade winds strengthen, upwelling increases and the eastern Pacific cools. This natural cycle, ENSO, shifts weather around the world.

Upwelling: when wind pushes surface water away from a coast, cold, nutrient-rich water rises from below. It makes coasts like Peru's some of the richest fisheries on Earth.
El Niño: weak trade winds, warm water spreads east, weak upwelling off South America; rain shifts east (floods in Peru, the southern United States wetter in winter), drought in Indonesia and Australia.
La Niña: strong trade winds, strong upwelling, a cooler-than-average eastern Pacific; the reverse effects (drought in Peru and the southern United States, heavy rain in Indonesia and Australia).
Together they are the El Niño-Southern Oscillation (ENSO), a natural cycle that swings every 2 to 7 years; each phase usually lasts about 9 to 12 months.
ENSO affects the whole world: El Niño years tend to be warmer globally and have fewer Atlantic hurricanes; La Niña years tend to have more.

warm water piles up near Indonesia, and cold, nutrient-rich water upwells off Peru warm water spreads east, upwelling off South America weakens and the eastern Pacific warms phytoplankton decline, so anchovies, seabirds and the fishing industry suffer Peru and Ecuador flood while Indonesia and Australia face drought and wildfire upwelling increases, the eastern Pacific cools and the rain stays farther west than normal

upwelling: The rise of cold, nutrient-rich deep water to the ocean surface, often where winds push surface water away from a coast, as off Peru. It supports rich fisheries.
El Niño: The warm phase of the El Niño-Southern Oscillation (ENSO): the trade winds weaken, warm water spreads east across the Pacific, upwelling off South America weakens and rain shifts east. It recurs every 2 to 7 years.
La Niña: The cool phase of ENSO: the trade winds strengthen, upwelling off South America increases, the eastern Pacific is colder than average and rain is heavier in the western Pacific.