Notes 11 – Plate Notes 11 – Plate TectonicsTectonics

Earth ScienceEarth Science

Mrs. GordonMrs. Gordon

Wednesday, April 19, 2023Wednesday, April 19, 2023

Review of Earth’s Layers:Review of Earth’s Layers:• Crust

– Oceanic Crust – ocean floor, made of dense basalt, thinner part of crust

– Continental Crust – less dense, mostly granite, thicker

• Asthenosphere – soft material that can flow like warm plastic

• Mantle • Core

– Outer core – liquid rock– Inner core – solid, very dense

metal

• NOTE: the inner and NOTE: the inner and outer core rotate and outer core rotate and create Earth’s magnetic create Earth’s magnetic fieldfield

Seafloor spreading reviewSeafloor spreading review

~ Wegener's evidence + discovery ~ Wegener's evidence + discovery of sea floor spreading led to:of sea floor spreading led to:

• A. The Theory of Plate TectonicsA. The Theory of Plate Tectonics - - pieces of Earth’s crust are in constant, pieces of Earth’s crust are in constant, slow motion driven by convection slow motion driven by convection currents in the mantle.currents in the mantle.

• Every plate affects the other plates around Every plate affects the other plates around it by colliding together, ripping apart or it by colliding together, ripping apart or grinding past each other.grinding past each other.

• 1. 1. The driving force of Plate Tectonics are The driving force of Plate Tectonics are CONVECTION CONVECTION CURRENTSCURRENTS. (Heat . (Heat RADIATES out from the core, RADIATES out from the core, warms mantle, material rises, then cools and sinks)warms mantle, material rises, then cools and sinks)

Convection means ‘heat transfer’. When a fluid heats up, the density decreases and it rises, eventually cooling, condensing and sinking again.

B.B. Where does Earths’ internal Where does Earths’ internal heat come from?heat come from?

• 1. 1. Radioactive DecayRadioactive Decay - - elements break down into other elements and release heat elements break down into other elements and release heat energyenergy

• 2. 2. Residual heatResidual heat - - left over from our planets formationleft over from our planets formation

C.C. What will happen when Earth’s What will happen when Earth’s internal heat runs out?internal heat runs out?

• No plate movementNo plate movement• No volcanoesNo volcanoes• No earthquakesNo earthquakes• No mountain buildingNo mountain building

• D. D. Plate Plate

BoundariesBoundaries – –

edges of edges of

Earth’s crustal Earth’s crustal

platesplates that that

extend deep extend deep

into the into the

lithospherelithosphere

Write these definitions, along with ARROWS showing directions of movement, on the left side page across from these notes – divide page into 4 sections.

• 1.1. Convergent Convergent BoundariesBoundaries - Where two - Where two

plates smash togetherplates smash together (results in the process of either (results in the process of either

subduction (trenches and subduction (trenches and volcanoes) or mountain building volcanoes) or mountain building (mountains)(mountains)– C-CC-C– O-CO-C– O-OO-O

• Subduction zonesSubduction zones – deep – deep trenches where one plate trenches where one plate slides under another. slides under another.

• The plate will melt as it is The plate will melt as it is pushed deep underground.pushed deep underground.

• 2.2. Divergent Boundaries Divergent Boundaries – Where plates – Where plates are ripping away from each other. are ripping away from each other.

• O-O = Results are mid-ocean ridgesO-O = Results are mid-ocean ridges (new (new ocean floor is formed here)ocean floor is formed here)

• C-C = Results are rift-valleysC-C = Results are rift-valleys

• 3.3. Transform Boundaries Transform Boundaries – Where plates – Where plates slide (grind) past each other in opposite slide (grind) past each other in opposite directions. directions. (San Andreas Fault)(San Andreas Fault)

THE BIG PICTURETHE BIG PICTURE

Old / Extra stuff:Old / Extra stuff:

How do we know what's inside How do we know what's inside Earth?Earth?

• Geologists use many different forms of indirect evidence to hypothesize what Earth’s interior is composed of.

• Ex: Earthquakes, seismic waves, plate movement, drilling

• Its tough to see first hand b/c as you go deeper underground both temperature and pressure increase.

• Cool link: Deep Drilling

• 1. Theory of Continental Drift – all continents were once connected and called Pangaea, they have since drifted apart.

• A. Alfred Wegener German scientist,1910

B.B. Evidence: Evidence:• Landforms, rock layers and

fossils match up across the oceans• Seafloor spreading • Observing

forces

happening

today

A. Sea Floor SpreadingA. Sea Floor Spreading

1. PROCESS =

~ Magma is forced upwards towards the crust, between two plates.

~ Magma fills the gap that is created.

~ Magma hardens to form new ocean crust.

2. EVIDENCE = molten material,

hydrothermal vents, magnetic

stripes, drilling samples