Drifting Continents Review Packet
Earth Science Review Unit 4: Dynamic Earth
Drifting Continents & Geological Clues
Name:
Date: Period:
Core Hypothesis (Alfred Wegener, 1912): Earth's continents were once assembled into a single supercontinent, Pangaea (Greek for "all Earth"), which began breaking apart ~200 million years ago. While coastline puzzle fits prompted the idea, rock record clues and stratigraphy provided the foundational physical proof.
1 The Four Pillars of Rock & Fossil Evidence
Analyze each evidence type and answer the prompt
A. Rock Type & Stratigraphy
Matching sedimentary rock layers in Brazil and South Africa share identical mineral composition, sequence, and depositional ages.
Why does matching stratigraphy rule out separate, isolated oceans?
B. Mountain Belt Alignments
The Appalachian Mountains (North America) directly align with the Scottish Highlands (Europe) in age, rock type, and folded rock structure.
What happened to this continuous mountain chain when Pangaea broke up?
C. Fossil Distribution
Glossopteris (heavy-seeded fern) and Mesosaurus (freshwater reptile) fossils are trapped in rock strata across South America, Africa, India, and Antarctica.
Why couldn't Mesosaurus simply swim across the modern Atlantic Ocean?
D. Glacial Bedrock Striations
Glacial gouges (striations) in bedrock and glacial sediment (tillite) are found in modern tropical regions of India, central Africa, and Australia.
What does glacial bedrock in the tropics prove about past continental location?
2 Scientific Scrutiny: Why Was Wegener Initially Rejected?
SEP: Engaging in Argument from Evidence
Wegener's Proposed Driving Force:
Claimed continents plowed directly through ___________________________like icebreakers, propelled by tidal forces and Earth's rotation.
Physicists' Rebuttal:
Oceanic ____________is far too dense and rigid for granite continents to plow through without shattering; tidal forces are billions of times too weak.
Speed Miscalculation:
Wegener estimated drift at \(250\text{ cm/yr}\). Actual plate motion is only \(2\text{--}5\text{ cm/yr}\) (fingernail growth rate).
Critical Thinking Reflection:
Carl Sagan famously noted that science requires "an openness to new ideas combined with ruthless skeptical scrutiny." Why was it scientifically valid for geologists to reject Wegener's hypothesis in 1915, despite his compelling rock evidence?
Dynamic Earth: Geological Clues & Continental Drift Page 1 of 3
Part 3 & 4
The Mechanism Unlocked & Misconception Buster
Harry Hess (1960s) · Sonar · Sea-Floor Spreading
3 Ocean Floor Basalt & The Sea-Floor Spreading Conveyor
Marine Geology Evidence
Mid-Atlantic Ridge: Basalt Age & Crust Recycling Model
Oldest Crust ~180 Ma (Near Trench)
Older Crust ~100 Ma
Ridge Axis 0 Ma (New Lava)
Older Crust ~100 Ma
Oldest Crust ~180 Ma (Near Trench)
← Subduction into Mantle Trench ← Divergent Motion | Magma Rises → Subduction into Mantle Trench →
1. Basalt Age Gradient Analysis:
How does the age of basalt rock change as you move farther away from the mid-ocean ridge axis in both directions?
2. Crust Conservation (Subduction):
If new rock is constantly formed at divergent ridges, why isn't Earth expanding in total volume?
4 Scientific Misconception Buster & Theory Matrix
Critical Misconception Alert
FALSE: "Tectonic plates float on a vast sea of boiling liquid magma."
SCIENTIFIC FACT: The asthenosphere is composed of SOLID ROCK (peridotite/silicates) under extreme heat and pressure. It behaves like an ultra-viscous plastic or silly putty over millions of years (solid plastic flow), NOT liquid magma. Magma chambers only exist in localized pockets!
Comparative Analysis: Continental Drift vs. Plate Tectonics Fill in the missing details for each theory
| Scientific Feature | Continental Drift (Alfred Wegener, 1912) | Plate Tectonics (Modern Theory) |
|---|
| 1. What is moving? Crust vs. Plates | | |
| 2. Driving Mechanism Forces causing motion | | |
| 3. Ocean Floor Role Static vs. dynamic | | |
| 4. Primary Evidence Key data supporting model | | |
Quick Verification Question: State the exact physical state of the asthenosphere and describe how solid rock can cause plate motion over millions of years:
Dynamic Earth: Seafloor Spreading & Plate Tectonics Model Page 2 of 3
Part 5 & 6
Plate Boundary Dynamics & CER Synthesis
Cause & Effect · Boundary Landforms · Scientific Argument
5 Plate Boundary Dynamics & Landform Engine
Complete the motion, geological processes, landforms, and examples
A. Divergent Boundary ← →
Geological Motion & Crust Process:
Landforms Created:
Real-World Example:
B. Convergent (Oceanic-Continental) → ←
Geological Motion & Crust Process:
Landforms Created:
Real-World Example:
C. Convergent (Continental-Continental) → ←
Geological Motion & Crust Process:
Landforms Created:
Real-World Example:
D. Transform Boundary ↑ ↓
Geological Motion & Crust Process:
Landforms Created:
Real-World Example:
6 Summative Scientific Argument (CER Task)
Claim · Evidence · Reasoning
Prompt: How do multiple independent lines of physical evidence (stratigraphy, fossils, and seafloor basalt) prove that Earth's tectonic plates move over geological time?
1. CLAIM (Directly answer the prompt in one clear statement):
2. EVIDENCE (Cite at least TWO specific physical data points from this review):
3. REASONING (Explain the scientific principles connecting the evidence to your claim):
Dynamic Earth: Plate Boundaries & CER Synthesis Page 3 of 3
