Tectonic Shifts Guided Notes
Earth & Space Science • Dynamic Earth Unit
Tectonic Shifts: Earth's Moving Crust
Interactive Fill-in-the-Blank Guided Notes & Structural Analysis
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Part 1 & 2 Word Bank (Terms may be used once or more)
Lithosphere • Asthenosphere • Continental Drift • Convection • Pangaea • Alfred Wegener • Basalt • Granite • Mesosaurus • Density • Plasticity • Glossopteris
1. The Mechanical Layers of the Earth
1. The rigid outer shell of the Earth consisting of the crust and uppermost mantle is called the . It is broken into tectonic plates.
2. Directly underneath lies the , a semi-fluid mantle layer where rock flows slowly under heat and pressure (a property called ).
| Layer | Physical State | Dominant Rock | Role in Tectonics |
|---|
| Continental Crust | Solid, brittle | | Thicker, less dense (floats higher) |
| Oceanic Crust | Solid, dense | | Thinner, denser (subducts downward) |
| Asthenosphere | | Silicate peridotite | Lubricates and carries rigid plates |
2. Continental Drift Hypothesis & Wegener's Evidence
In 1912, meteorologist proposed that all continents were once connected in a single supercontinent called before slowly breaking apart.
A. Continental Puzzle Fit
The Atlantic coastlines of South America and fit together remarkably well.
B. Fossil Correlation
Fossils of freshwater were found across separated oceans.
C. Mountain Belts
Rock ages in North America's Appalachians match mountain chains in .
D. Paleoclimate Clues
Glacial scratches exist in tropical India; tropical coal beds lie in frozen .
Critical Flaw: Why did the scientific community reject Wegener's idea?
Although Wegener documented compelling evidence, he could not identify the or force capable of plowing continents through the sea floor.
Summary sentence:
Unit 3 • Dynamic Earth Science Page 1 of 2
Mechanism & Boundary Dynamics
Plate Driving Forces & Boundary Interactions
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3. The Earth's Heat Engine: Mantle Convection Currents
The primary mechanism powering plate motions is within the asthenosphere, driven by intense heat from Earth's core.
Step 1: Heating
Deep mantle rock heats, expands, and becomes dense.
Step 2: Rising
The warm, buoyant mantle material slowly upward.
Step 3: Drag
Lateral cooling currents pull overlying plates via .
Step 4: Sinking
Cold, dense oceanic crust sinks down by pull.
4. The Three Primary Plate Boundary Types
Divergent ← | →
Motion: Plates move each other.
Crust Effect: New crust is (constructive).
Features: Mid-ocean ridges, rift valleys, fissure vents.
Real Example:
Convergent → | ←
Motion: Plates or collide.
Crust Effect: Lithosphere is or folded.
Features: Deep trenches, volcanic arcs, mountain chains.
Real Example:
Transform ⇅
Motion: Plates slide horizontally.
Crust Effect: Crust is neither nor destroyed.
Features: Fault fracture lines, shallow severe earthquakes.
Real Example:
5. Hotspots & The Pacific Ring of Fire
1. An unusually hot, stationary magma plume rising through the mantle creates a . As a plate drifts across it, a volcanic island chain forms (e.g., the Islands).
2. The active horseshoe basin surrounding the Pacific Ocean containing over 75% of Earth's volcanoes is called the .
Synthesis & Critical Reasoning
When an oceanic plate collides with a continental plate, why does the oceanic plate always subduct beneath the continental plate? Explain using the concept of density.
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