APES - Unit 4: Earth Systems and Resources

Earth’s structure from inner to outer

1. Core

2. Mantle - 3 layers:

   1. Magma

   2. Asthenosphere

   3. Lithosphere

      • Crust (lithosphere’s outer layer)

core

dense mass of nickel, iron, & radioactive elements that release massive amounts of heat

mantle

bulk of Earth’s interior; 3 layers = magma, asthenosphere, & lithosphere

magma

molten rock (slowly circulates to be heated by core)

asthenosphere

semi-molten, flexible, liquidy

lithosphere

thin, brittle rock floating on top of mantle (broken into tectonic plates); top of mantle + all of crust

crust

outer layer of lithosphere; Earth’s surface

divergent plate boundary

plates move away from each other - forced apart by rising magma plume from mantle

• forms mid-oceanic ridges (magma comes up to form these mountains), volcanoes, seafloor spreading (spreading zones; new seafloor formed by magma), rift valleys (on land)

convergent plate boundary

plates move toward each other, leading to subduction (one plate being forced beneath another)

• forms mountains, island arcs, & volcanoes

transform fault plate boundary

plates slide sideways past each other, sometimes causing earthquakes

• forms faults (fractures in rock)

mantle convection currents steps

1. magma heated by the core rises to the lithosphere b/c less dense, forcing oceanic plates apart - creates midocean ridges, volcanoes, & spreading zones/seafloor spreading

2. magma cools, gets pushed to sides by new magma coming up

3. solidifies into new lithosphere at the spreading zone

4. spreading magma moves plates b/c they sit on top - forces oceanic plate under continental plate

   • divergent boundary at the convection current; convergent when they get pushed together by 2 different convection currents

5. sinking oceanic plate melts back into magma

6. new magma is forced up, creating narrow, coastal mountains

types of convergent boundaries

oceanic-oceanic, oceanic-continental, & continental-continental

oceanic-oceanic convergent boundary

1 plate subducts underneath the other, forcing magma up to surface of lithosphere - forms mid-ocean volcanoes (island arcs) & creates off-shore trench

oceanic-continental convergent boundary

dense oceanic plate subducts beneath a continental plate & melts back into magma, forcing new magma up to lithosphere surface

• forms coastal mountains (Andes), volcanoes on land, trenches, & tsunamis

continental-continental convergent boundaries

surface crust from both plates “buckles” upward, creating mountains (ex. Himalayas)

What causes earthquakes?

1. rough edges of transform fault boundaries get stuck on each other

2. pressure builds as plates keep sliding but edges are still stuck

3. when stress overcomes locked fault, plates suddenly release - slide past each other & release energy that shakes the lithosphere

What can a tectonic map predict?

ring of fire, transform faults (likely earthquake location), hotspots

Ring of Fire

pattern of volcanoes & earthquake zones all around pacific plate

• especially offshore island arcs (ex. Japan)

hotspots

areas of especially hot magma rising to the lithosphere

• at mid-ocean islands (ex. Iceland, Hawaii)

Why does subduction happen at some types of plate boundaries but not others?

happens at oceanic-continental & oceanic-oceanic convergent boundaries, but not at continental-continental ones b/c the plates have the same density (creates mountains instead)

Does the Earth ever grow bigger from the phenomena at plate boundaries? Why/why not?

No, b/c the magma coming up and crust going back down balance each other out

What is soil made out of?

mix of geologic (rock) & organic (living) components

• sand, silt, clay, humus (organic part; broken down biomass), nutrients, water, air, & living organisms

How is soil formed?

• from below: weathering of plant material creates smaller fragments that make up geological/inorganic part of soil

  • sand, silt, clay, minerals

• from above: breakdown of organic matter adds humus, & erosion deposits soil particles from elsewhere

Soil horizons from top to bottom + potential measures

1. O-horizon: 0-0.1 m

2. A-horizon/topsoil: 0.1-0.3 m

3. B-horizon/subsoil: 0.3-1 m

4. C-horizon/bedrock: 1-1.3 m

*some soils have an E-horizon below either O or A

O-horizon

layer of organic matter (plant roots, dead leaves, animals waste, etc.) on top of soil; provides nutrients & limits H₂O loss to evaporation

A-horizon

aka topsoil; layer of humus & minerals from parent material; has most biological activity (earthworms, soil microbes, etc.), which break down organic matter to release nutrients

B-horizon

aka subsoil; lighter layer below topsoil, mostly made of minerals with little to no organic matter; contains some nutrients

C-horizon

sometimes called bedrock; least weathered soil; closest to parent material

soil degradation

loss of soil’s ability to support plant growth

• loss of topsoil, compaction, nutrient depletion

loss of topsoil

tilling (turning soil for agriculture) & loss of vegetation disturb the soil; dries out the soil so more easily eroded by wind/rain; removes nutrients & soil organisms that recycle nutrients

compaction

soil compression by machines (tractors, bulldozers, etc.), grazing livestock, & humans - reduces ability to hold moisture, erodes easier b/c:

1. dry soil erodes easier

2. supports less plant growth/root structure - more erosion

nutrient depletion

repeatedly growing crops on the same soil removes key nutrients (N, P, K, Na, Mg) over time, reducing its ability to grow future crops