AP Environmental Science Topic 4.1-3

Goes over Plate Tectonics, Soil Formation, Erosion, Soil Composition, and Soil Properties.

Parts of Earth’s Structure

• Core

• Mantle

• Asthenosphere

• Lithosphere

• Crust 

Core

Dense mass of solid nickel, iron, and radioactive elements that release a massive amount of heat.

Mantle

Liquid layer of magma surrounding the core.

• Kept liquefied by the core’s intense heat.

Asthenosphere

Solid, flexible, plastic-like outer layer of the mantle, beneath the lithosphere.

Lithosphere

Thin, brittle layer of rock floating on top of the mantle.

• Broken up into tectonic plates.

Crust

The very outer layer of the lithosphere.

• Earth’s surface.

Divergent Plate Boundary

When the plates move away from each other.

Cause of Divergent Plate Boundary

Rising magma plume from the mantle forces the plates apart.

Divergent Plate Boundaries form…

• Mid-Ocean Ridges

• Volcanoes

• Seafloor Spreading

• Rift Valleys (on land)

Convergent Plate Boundary

When the plates move towards each other.

Convergent Plate Boundaries form…

• Mountains

• Island Arcs

• Earthquakes

• Volcanoes

Subduction

When one plate is forced underneath another.

Transform Fault Plate Boundary

When the plates slide past each other in opposite directions.

Transform Fault Plate Boundaries form…

Earthquakes

Types of Convergent Boundaries

• Oceanic-Oceanic

• Oceanic-Continental

• Continental-Continental

Subduction Zone = …

… Convergent Boundary

Oceanic-Oceanic Boundary

When one plate subducts under another.

Effects of Oceanic-Oceanic Boundaries

• Magma is forced up to lithosphere and surface.

Oceanic-Oceanic Boundaries form…

• Mid-Ocean Volcanoes

• Island Arcs

• Off-Shore Trenches

Oceanic-Continental Boundary

When a dense oceanic plate subducts under a continental plate and then melts back into the magma.

Effects of Oceanic-Continental Boundary

• Magma is forced up to the lithosphere surface.

Oceanic-Continental Boundaries form…

• Coastal Mountains (e.g. Andes)

• Volcanoes (on land)

• Trenches

• Tsunamis

Continental-Continental Boundary

One plate subducts under another, forcing surface crust upward.

Continental-Continental Boundaries form…

• Mountains (e.g. Himalayas)

Tectonic Map can Predict…

• Ring of Fire

• Transform Faults

• Hotspots

Ring of Fire

The pattern of volcanoes all around the pacific plate.

• e.g. Offshore island arcs in Japan

Transform Faults

The likely location of earthquakes.

Hotspots

Areas of very hot magma rising up to the lithosphere.

• e.g. Mid-ocean islands in Iceland and Hawaii

Soil

A mixture of geologic (rock) and organic (living) components.

What is soil made up of?

• sand 

• silt

• clay

Humus

The main organic part of soil.

• Broken down biomass.

What nutrients are found in soil?

• ammonium

• phosphates

• nitrates

What does soil do for plants?

• anchors roots

• gives water, shelter, and nutrients

What does soil do for water?

Filters rainwater and runoff by trapping pollutants in pore spaces and plant roots.

What does soil do for nutrient recycling?

Houses decomposers that break dead organic matter down and return nutrients to soil.

What kinds of organisms does soil house?

• earthworms

• fungi

• bacteria

• moles

• slugs

Weathering

Breaking rocks down into smaller pieces.

• Happens from below (bottom-up)

Physical Weathering

E.g. wind, rain, ice freezing/thawing breaks rocks down into soil

Biological Weathering

Tree roots crack rocks and break them down into soil

Chemical Weathering

Acid rain, mass/lichen acids breaking down rock into soil

Erosion

Transport of weathered rock fragments by wind and rain.

• Happens from above (top-down)

Deposition

When weathered rock fragments are carried to new location and deposited.

Makes up geological/inorganic part of soil

Weathering

Breakdown of organic matter adds humus to soil

Erosion

Topography

The land’s slope.

How does parent material affect soil formation?

Affects pH and nutrient content.

How does topography affect soil formation?

• steep slope = too much erosion

• level ground = deposition

How does climate affect soil formation?

• warmer = faster organic matter breakdown

• more precipitation = more weathering, erosion, and deposition 

How do organisms affect soil formation?

Organisms like bacteria, fungi, and worms break organic matter down.

O-Horizon

Layer of organic matter on top of soil.

O-Horizon characteristics 

Provides nutrients and limits water loss to evaporation.

A-Horizon

Layer of humus and minerals from parent material.

• AKA topsoil

A-Horizon characteristics

Has most biological activity breaking down organic matter to release nutrients.

B-Horizon

Lighter layer below topsoil.

• AKA subsoil

B-Horizon characteristics

• Mostly made of minerals

• Some nutrients

• Little to no organic matter

C-Horizon

Least weathered soil that’s closest to parent material (bedrock).

What causes topsoil loss?

Tilling and vegetation loss disturbs soil, making it more easily eroded by wind and rain.

Soil Degradation

Soil’s loss of ability to support plant growth.

Topsoil loss…

• dries soil out

• removes nutrients and soil organisms that recycle nutrients

Compaction

Compression of soil by machines, grazing livestock, and humans which reduces its ability to hold moisture.

Compaction leads to…

• Easily eroding soil 

• Able to support less plant growth

• Less root structure

Nutrient Depletion

Repeatedly growing crops on the same soil removes key nutrients over time.

Soil Texture

Percentages of sand, silt, and clay in soil.

Pores

Empty spaces in between particles.

Has biggest pores (in soil)

sand

Has smallest pores (in soil) 

clay

Has medium-sized pores (in soil)

silt

Porosity

Amount of pore space soil has.

Permeability

How easily water drains through soil.

Water Holding Capacity

How well soil holds water.

Ideal soil for plants

Loam because it balances porosity with water holding capacity.

Soil that’s too sandy…

Drains water too quickly for plant roots and dries out.

Clay-heavy soil…

Doesn’t let water drains to roots/water logs.

Factors that increase soil nutrients

• organic matter

• humus

• decomposer activity

• clay

• bases

Factors that decrease soil nutrients

• acids

• excessive rain/irrigation

• excessive farming

• topsoil erosion

Factors that increase water holding capacity

• aerated soil

• compost/humus/organic matter

• clay content

• root structure

Factors that decrease water holding capacity

• compacted soil 

• topsoil erosion 

• sand 

• root loss