Unit 4 APES

Core

Dense mass of nickel, iron, and radioactive elements that release massive amounts of heat

Mantle

bulk of Earth’s interior; three layers

Magma, Asthenosphere, Lithosphere

Magma aka (molten rock)

layer that slowly circulates due to heat from core

Asthenosphere

semi-molten, flexible outer layer of mantle, beneath the lithosphere

Lithosphere

thin, brittle layer of rock floating on top of mantle (broken up into tectonic plates)

Crust

very outer layer of the lithosphere, Earth’s surface

Divergent Plate Boundary

• plates move away from each other

• Rising magma plume from mantle forces plates apart

Forms: mid-oceanic ridges, volcanoes, seafloor spreading, and rift valleys (on land)

Transform Fault Plate Boundary

• Plates slide sideways past each other (earthquakes)

Forms: faults (fracture in rock)

Convergent Plate Boundary

• Plates move towards each other

• Leads to subduction (one plate being forced beneath another)

Forms: mountains, island arcs, and volcanoes

Movement of Core-Heated Magma

Magma heated by Earth's core rises towards the lithosphere.

Effect of Rising Magma on Oceanic Plates

Rising magma forces oceanic plates apart.

Features Created by Oceanic Plates Spreading

Creates mid-ocean ridges, volcanoes, spreading zones, or "seafloor spreading".

Formation of New Lithosphere

Magma cools and solidifies into new lithosphere at the spreading zone.

Oceanic & Continental Plate Interaction

Spreading magma forces the oceanic plate under the continental plate.

Fate of the Sinking Oceanic Plate

Sinking oceanic plate melts back into magma.

Landforms Created by Upward-Forced Magma

New magma is forced up, creating narrow, coastal mountains (e.g., Andes) & volcanoes on land.

Mantle Convection Currents (visual)

Oceanic-Oceanic

one plate subducts underneath other:

Forces magma up to lithosphere surface, forming mid ocean volcano

• Island arcs

Off-shore trench

Oceanic-Continental

dense oceanic plate subducts beneath cont. Plate & melts back into magma

• Forces magma up to lithosphere surface

• Coastal Mountains (Andes), Volcanoes on land, trenches, tsunamis

Continental-Continental

surface crust from both plates “buckles” upward (mountains)

• Ex: Himalayas

Transform Fault Boundary

Plates sliding sideways past each other; can create a fault (fracture in rock surface)

what does Transform Fault Boundary cause

• Earthquakes occur when rough edges of plates get stuck on each other

• Pressure builds as plates keep sliding, but edges stay stuck

• When stress overcomes the locked fault, plates suddenly release, slide past each other and release energy that shakes the lithosphere

Ring of Fire

pattern of volcanoes & earthquake zones all around pacific plate

• Offshore island arcs (Japan)

Transform faults

likely location of earthquakes

Hotspots

areas of especially hot magma rising up to lithosphere

• Mid-ocean Islands (Iceland, Hawaii)

Plants

anchors roots of plants and provides water, shelter, nutrients (N, P, K, Mg) for growth

Water

filters rainwater + runoff by trapping pollutants in pore spaces + plant roots. Clean water enters groundwater + aquifers

Nutrient Recycling

home to decomposers that break down dead organic matter + return nutrients to the soil

Habitat

provides habitat for organisms like earthworms, fungi, bacteria, moles, slug

What is Soil?

Mix of geologic (rock) and organic (living) components

What is soil made up of

• Sand, silt, clay

• Humus

• Nutrients

• Water and Air

• Living Organisms

Humus

main organic part of soil (broken down biomass like leaves, dead animals, waste, etc.)

Nutrients

ammonium, phosphates, nitrates

Weathering

Breakdown of rocks into smaller pieces

physical weathering

Physical (wind, rain, freezing/thawing of ice

biological weather

Biological (roots of trees crack rocks)

chemical weathering

Chemical (acid rain, acids from moss/lichen)

how does weathering of rocks lead to soil formation

• Broken into smaller and smaller pieces

• Carried away and deposited by erosion

Erosion

• Transport of weathered rock fragments by wind and rain

• Carried to new location and deposited (deposition)

Soil Formation (from below)

Weathering of parent material produces smaller, and smaller fragments that make up geological/inorganic part of soil

• Sand, silt, clay

• Minerals

Soil Formation (from above)

• Breakdown of organic matter adds humus to soil

• Erosion deposits soil particles from other areas, adding to soil

Effects on Soil Formation (Parent material)

soil pH, nutrient content 

Effects on Soil Formation (Topography)

steep slope = too much erosion;

more level ground = deposition

Effects on Soil Formation (Climate)

warmer = faster breakdown of org. matter;

more precip. = more weathering, erosion + deposition

Effects on Soil Formation (Organisms)

Soil organisms like bacteria, fungi, worms breakdown organic matter

How does the texture and structure of soil affect its properties?

• Texture (the proportion of sand, silt, and clay) dictates pore size. Sandy soils drain quickly and retain few nutrients, while clay-rich soils hold water and nutrients tightly but can become waterlogged due to poor aeration.

• Structure (how soil particles aggregate together) determines how easily water, air, and plant roots can move through the soil. Good structure balances aeration with water retention.

3. What role do microorganisms play in soil?

Microorganisms (bacteria, fungi, actinomycetes) decompose organic matter, break down rocks chemically, cycle essential nutrients (like nitrogen, phosphorus, and sulfur) into forms plants can absorb, and improve soil structure by helping form aggregates.

4. How do soils help with climate regulation?

Soils act as a massive carbon sink. They store organic carbon from plant tissues and trap roughly 25% of the carbon dioxide produced by human fossil fuel emissions, preventing it from entering the atmosphere and contributing to global warming.

5. What does the color of a soil signify? How does color relate to drainage?

Color Signification: Soil color reflects its chemical composition and organic content.

• Dark brown or black indicates high organic matter (humus).

• Red indicates well-oxidized iron minerals (like rust).

• Yellow indicates hydrated iron minerals.

• Gray/blue indicates reduced iron caused by waterlogging.

Relation to Drainage: Bright red and brown subsoils signify good aeration and well-drained conditions. Grayish or mottled subsoils signify poor drainage, frequent saturation, and oxygen depletion.

1. Briefly explain how soil is formed.

Soil forms through the physical and chemical breakdown (weathering) of bedrock or parent materials combined with the accumulation and decomposition of organic matter from plants and organisms over long periods.

2. What gives soils their chemical properties?

The chemical properties of soil come from its parent material (the mineral content of the original rock) and the chemical transformations driven by water, weathering, organic acid release, and microorganism activity.

3. How long does the process take to form soil?

Soil formation is extremely slow. It typically takes hundreds to thousands of years to form just a few centimeters of topsoil.

4. What does ClORPT stand for?

ClORPT stands for:

Cl – Climate

O – Organisms

R – Relief (Topography/Landscape)

P – Parent Material

T – Time

5. How does climate affect soil formation?

Temperature and precipitation dictate the speed of chemical weathering and organic matter decomposition. Warm, moist climates speed up weathering and plant growth, while cold or arid climates slow down soil formation. Water flow also causes leaching (movement of nutrients downward).

6. How do organisms affect soils?

Plants add organic matter, bind particles together with roots, and prevent erosion. Animals, earthworms, and insects aerate, turn, and mix the soil. Microbes decompose organic detritus into humus and release plant-available nutrients.

7. What is “relief” and how does it affect soil formation?

Relief refers to the slope, elevation, and orientation (aspect) of the landscape. Steep slopes lose soil quickly due to water runoff and erosion (resulting in thin soils), whereas flat valley bottoms accumulate eroded material and water, forming deeper, richer soils.

8. Where can the parent material for a soil come from?

Parent material can come from underlying bedrock (like granite, sandstone, or limestone) or transported sediments carried in by wind (loess), water (alluvium), glaciers (glacial till), or gravity (colluvium).

9. How can time affect soils?

As time progresses, soils become more developed, deeper, and exhibit distinct layers (horizons). Younger soils closely resemble their parent rock, whereas older soils are heavily influenced by climate and biological activity.

O Horizon

Organic layer ( (plant roots, dead leaves, animal waste, etc) on top of soil

composed of loose leaf litter, twigs, and decomposing matter.

Provides nutrients and limits H2O loss to evaporation

A Horizon

ka topsoil; layer of humus (decomposed organic matter) and minerals from parent material

• A-Horizon has most biological activity (earthworms, soil microbes) breaking down organic matter to release nutrients

B-Horizon:

aka subsoil; lighter layer below topsoil, mostly made of minerals w/little to no org. matter

Contains some nutrients

• "Zone of Accumulation" rich in leached minerals, iron, and clay.

E Horizon

Eluviation (leaching) layer; light-colored layer depleted of minerals and clay.

C Horizon

least weathered soil that is closest to the parent material, sometimes called bedrock

• Substratum

R Horizon

Bedrock; unweathered, solid rock layer beneath the soil profile.

2. What types of material makes up the O Horizon?

Organic matter such as decomposing leaves, twigs, plant litter, moss, peat, and animal matter.

3. How is the A Horizon different from the O? What is eluviation and what causes it?

Difference: The O horizon is almost pure organic litter, whereas the A Horizon (topsoil) is a mix of decomposed organic matter combined with mineral particles (sand, silt, clay).

Eluviation: The process by which water percolating downward washes away soluble nutrients, iron, aluminum, and clay particles from an upper layer (forming the E Horizon). It is caused by rainwater moving down through the soil profile.

4. What is the common process occurring in the B Horizon? Why is it called the “Zone of Accumulation”?

Process: Illuviation (the deposition and collection of materials washed down from above).

Why it's called Zone of Accumulation: Minerals, clay, iron, and organic acids that leached out of the A and E horizons collect and concentrate in the B Horizon.

5. How are the C & R Horizons related?

The R Horizon (solid bedrock) slowly breaks down through physical and chemical weathering to form the C Horizon (partially weathered rock fragments). The C Horizon sits directly on top of the R Horizon.

1. Explain the difference between weathering and erosion.

Weathering: The physical or chemical breaking down of rocks and minerals into smaller pieces in place (no movement).

Erosion: The physical transport or removal of soil and weathered rock particles from one location to another by wind, water, ice, or gravity.

2. What are the two types of weathering?

Mechanical (Physical) Weathering: Breaking rocks into smaller pieces without changing their chemical structure (e.g., frost wedging, root expansion).

Chemical Weathering: Changing the internal chemical composition of rocks through chemical reactions (e.g., oxidation, dissolution by acid rain).

3. Give examples of slow erosion and rapid erosion.

Slow Erosion: Wind carrying soil particles across a plain over decades, or slow sheet wash from gentle rain.

Rapid Erosion: Mudslides, landslides, flash floods washing away riverbanks, or extreme gully erosion after a heavy storm.

4. Four Categories of Soil Ecosystem Services:

Regulating Service: Climate regulation (carbon storage) or flood mitigation.

Provisional Service: Providing food, fiber, fuel, and timber via plant growth.

Supporting Service: Nutrient cycling and soil formation.

Cultural Service: Providing land for recreation, green spaces, and preserving archaeological artifacts.

5. How do soils aid in water filtration?

As water passes down through soil layers, physical pore spaces trap suspended solids and sediments, while clay particles and organic matter chemically adsorb toxins, heavy metals, and excess nutrients before the water recharges underground aquifers.

6. Explain the relationship between soil ecosystem services and biodiversity.

High soil biodiversity (a diverse network of microbes, fungi, and insects) drives effective nutrient cycling, improves soil structure, and prevents disease. This biodiversity is what enables soils to deliver vital ecosystem services like clean water, fertile crops, and carbon capture.

Loss of Topsoil:

tilling (turning soil for agriculture) + loss of

vegetation disturb soil and make it more easily eroded by wind and rain

• Loss of top soil dries out soil, removes nutrients + soil organisms that recycle nutrients

Compaction

compression of soil by machines (tractors, bulldozers, etc.), grazing livestock, and humans reduces ability to hold moisture

• Dry soil erodes more easily

• Dry soil supports less plant growth, less root structure, leading to more erosion

Soil Salinization

Soil salinization occurs when there is a gradual increase, gain, or accumulation of soluble salts in the soil. Can happen with over watering as the water evaporates and leaves salts behind

Nutrient Depletion:

repeatedly growing crops on the same soil removes key nutrients (N, P, K, Na, Mg) over time

Reduces ability to grow future crops

Geologic (rock) portion of soil is made up of 3 particles:

(biggest to smallest) Sand > silt > clay

Soil Texture:

is the % of sand, silt, and clay in a soil

Always adds up to 100% ex: 40-40-20

Soil Pores:

empty spaces between particles

• Because sand is bigger, it has bigger pores that are connected to each other

This allows air + water to enter sandy soil easily

• Clay has smaller, unconnected pores, so it’s harder for air + water to enter clay-heavy soils

Permeability

how easily water drains through a soil

Pore space:

arger, connected pore spaces = greater permeability

H2O Holding Capacity

how well water is retained, or held by a soil

• More permeable = lower H2O holding capacity

• Inverse relationship between permeability and H2O holding capacity

Pore space, Permeability, and H2O Holding Capacity Effect on Soil Fertility

• Soil that is too sandy (too permeable) drains water too quickly for roots + dries out

• Clay-heavy soil doesn’t let H2O drain to roots, or waterlogs (suffocating them)

• Ideal soil for most plant growth is loam, which balances porosity or drainage, with H2O holding cap.

Soil Fertility

ability of soil to support plant growth

Nutrients of soil

• N, P, K+, Mg2+, Ca2+, Na+

• Factors that increase soil nutrients

Organic matter (releases nutrients)

Humus (holds and releases nutrients)

Decomposer activity (recycles nutrients)

Clay (neg. charge binds pos. nutrients)

Bases (Calcium carbonate - limestone)

• Factors that decrease soil nutrients

Acids leach positively charged nutrients

Excessive irrigation leaches nutrients

Excessive farming depletes nutrients

Topsoil erosion

Water in soil

Needs to hold water, but not too much

• Factors that increase H2O holding cap.

Aerated soil (biological activity)

Compost/humus/organic matter

Clay content

Root structure, especially natives

• Factors that decrease H2O holding cap.

Compacted soil (machines, cows)

Topsoil erosion

Sand

Root loss

Texture

• Let soil settle in jar of water. Measure 3 layers that form (sand, silt, clay)

• % of sand, silt, and clay - how porous or permeable soil is

Permeability

• Time for H2O to drain through column of soil

• How easily water drains through soil. Too high, soil dries out. Too low, roots don’t get water or drown. Medium = optimal (loam)

pH

pH strip - H+ ion concentration

How acidic (low pH) or basic/alkaline (high pH) soil is. More acidic soil = less nutrient availability

Color

Compare w/soil book color chart

The darker, the more humus.

the more nutrients and moisture

Nutrient Level

Measure ammonium, nitrate, or phosphate level

Higher nutrient levels = more plant growth.

Low level could indicate acidic soil, deple

Nitrogen in atmosphere

makes up 78%

• Mostly in the form of N2 (unuseable to plants without being fixed)

  
  

Oxygen in atmosphere

makes up 21%

Produced by photosynthesis in plants & needed for human/animal respiration

Argon in atmosphere

makes up .93%

• Inert, noble gas

CO₂ atmosphere

Most important GHG; leads to global warming

Removed from atm. by photosynthesis

Water Vapor in atmosphere

makes up 0.4%

Varies by region & conditions; acts as a temporary GHG, but less concerning than CO2

Quickly cycles through atmosphere