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Final Draft: Why Does Earth’s Surface Look the Way It Does?

Mary Clark

Created on September 4, 2025

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Transcript

The Case of the Moving Continents

Start

Case Notes: 1912

At the beginning of the twentieth century, scientists noticed puzzling patterns in Earth’s surface features that seemed to link distant continents. However, no accepted explanation existed. In 1912, Alfred Wegener examined these clues and proposed a bold idea about how Earth had changed over time — an idea many scientists questioned. Today, you will revisit the same clues and evaluate whether the patterns point to a single scientific explanation.

Detective Challenge

Your Mission: If someone told you continents move, what evidence would convince you this was true? Detective Journal: □ List at least 3 clues that could prove continents move. □ Circle your strongest piece of evidence.

Case File 1912

#1: Continental Fit

Study the continental shapes and record your observations in your Evidence Collection Sheet.

#2: Fossil Evidence

Explore each fossil location to examine Wegener's most compelling evidence. As you explore, record your observations in your Evidence Collection Sheet.

Mesosaurus

Mesosaurus was a small reptile, about 1 meter (3 feet) long, that lived approximately 280 million years ago. It had a long tail, webbed feet, and sharp teeth designed for catching fish. Important detail: Mesosaurus lived in freshwater lakes and rivers. It could not survive in saltwater. Where it lived: Water (freshwater rivers and lakes).

Glossopteris

What it was: A seed fern with tongue-shaped leaves. When it lived: Late Permian (~260 million years ago). Where it lived: Land (grew in swamps and floodplains).

Cynognathus

What it was: A dog-sized carnivorous therapsid (mammal-like reptile that could not swim). When it lived: Early to Middle Triassic (~250–240 million years ago). Where it lived: On land.

Lystrosaurus

What it was: A pig-sized, plant-eating reptile (a therapsid — a mammal-like reptile). When it lived: Late Permian to Early Triassic (~260–250 million years ago). Where it lived: On land.

#3: Glacial Evidence

Click on each glacier location to investigate. Record your observations in your Evidence Collection Sheet.

South America

Late Paleozoic glacial striations (300 Ma) carved when ice sheets covered this region. The parallel scratches show the direction of ice movement. Today: Tropical Brazil with rainforests Then: Part of Gondwana's polar ice cap.

What was Gondwana?

What are glacial striations?

Africa

300-million-year-old glacial striations from the Dwyka Ice Age. These scratches were carved when massive ice sheets covered southern Africa. Today: Hot, dry Karoo desert region

What was Gondwana?

What are glacial striations?

Australia

280-million-year-old glacial scratches carved when massive ice sheets covered this area. The grooves show ice moved from SE to NW. Today: Warm coastal climate, no glaciers for thousands of miles.

What was Gondwana?

What are glacial striations?

#4: Rock Evidence

Select each glacier location to investigate. Record your observations in your Evidence Collection Sheet.

Amazonia

Rock Types: Granites, metamorphic rocks, and volcanic greenstone belts. Age: 2.0-2.1 billion years old Mountain-Building Event: Major continental collision around 2.0-2.1 billion years ago. Special Feature: Contains a belt of metamorphosed volcanic and sedimentary rocks created during this collision.

São Francisco

Rock Types: Ancient granites, gneisses, and metamorphic rocks. Age: 2.0-2.5 billion years old (some rocks up to 3.4 billion years) Mountain-Building Event: Multiple ancient events. Special Feature: Experienced major volcanic eruptions at 1,500 million, 1,380 million, and 1,110 million years ago. Contains distinctive walls of volcanic rock (dyke swarms) from these eruptions.

Rio de la Plata

Rock Types: Granites and metamorphic rocks. Age: 2.1-2.2 billion years old (very uniform age). Mountain-Building Event: Ancient orogeny around 2.1 billion years ago. Special Feature: Made of "juvenile crust" (new rock formed from magma, not recycled). Later collided with another landmass around 545 million years ago.

West Africa

Rock Types: Granites, metamorphic rocks, and volcanic greenstone belts. Age: 2.0-2.1 billion years old. Mountain-Building Event: Major continental collision around 2.0-2.1 billion years ago. Special Feature: Contains a belt of metamorphosed volcanic and sedimentary rocks created during this collision.

Congo

Rock Types: Ancient granites, gneisses, and metamorphic rocks. Age: 2.0-2.5 billion years old (some rocks up to 3.6 billion years). Mountain-Building Event: Multiple ancient events. Special Feature: Experienced major volcanic eruptions at 1,500 million, 1,380 million, and 1,110 million years ago. Contains distinctive walls of volcanic rock (dyke swarms) from these eruptions.

Kalahari

Rock Types: Granites and metamorphic rocks. Age: 2.0-3.6 billion years old with major rocks at 2.1-2.2 billion years. Mountain-Building Event: Ancient orogeny around 2.1 billion years ago. Special Feature: Made of "juvenile crust" (new rock formed from magma, not recycled). Later collided with another landmass around 545 million years ago.

#5: Fatal Flaw

Despite compelling evidence, Wegener had one fatal flaw: he couldn't explain how continents plowed through solid rock.

#6: Case Reopened

For decades, Wegener’s idea remained rejected… until new technologies let scientists explore the seafloor and Earth’s interior in ways he never could. What they found reopened the case — and transformed Earth science forever. Click each icon on the map to investigate the new evidence that finally proved the continents move.

Earthquake Clues

Scientists collected global earthquake locations and created maps like this one. Look closely at where earthquakes happen around the world. What patterns do you notice? Record your observations in your Evidence Collection Sheet.

Earthquake Depth

Scientists recorded the depths of earthquakes around the world. On this map, each dot shows an earthquake, and the colors show how deep it occurred. Study the map carefully. Where do the deepest earthquakes occur? What patterns do you notice? Record your observations in your Evidence Sheet.

Mid-Ocean Ridge

Using sonar, scientists mapped the ocean floor and found long mountain chains running through the middle of the oceans. Examine this image of the seafloor. What do you notice about the shape and arrangement of these ridges? Add your observations to your Evidence Sheet.

New Technology - The Magnetometer

Sometimes the biggest breakthroughs come from unexpected places. The military had been towing devices called magnetometers across the ocean floor. These devices measure magnetic fields in rocks. They were mapping the ocean floor for submarine detection - but they had no idea they were about to revolutionize geology.

The Accidental Discovery

What the military found shocked scientists. When scientists analyzed the military's magnetometer data, they discovered something completely unexpected: mysterious magnetic stripe formations across the ocean floor! This accidental military discovery would soon provide the key to solving Wegener's 50-year-old mystery.

Magnetic Rock Evidence

Scientists realized these rocks were like a magnetic recording device. When hot volcanic rock cools and hardens on the ocean floor, tiny magnetic minerals inside act like compass needles - they align with Earth's magnetic field and get "frozen" in place forever. This means scientists can read these ocean floor rocks like a history book of Earth's changing magnetic field!

Earth's Magnetic Field Flips

Here's the surprising part: Earth's magnetic field has flipped many times throughout history! Sometimes it points north (like today), and sometimes it points south. Each colored stripe represents rock that formed when Earth's magnetic field was pointing in a different direction: Colored Stripes = formed when magnetic field pointed north. White Stripes = formed when magnetic field pointed south.

Crack the Code - Pattern Analysis

Your turn to be the detective. What do you notice? Scientists discovered these magnetic patterns at the underwater mountain ranges around the world. Study the evidence carefully. What patterns do you see developing over time? 🔍Detective Journal Entry #10: Record your observations about these patterns.

The Breakthrough - Seafloor Spreading

Congratulations, detective! You've made the same discovery that revolutionized Earth science. Your observation of perfect symmetry led scientists to a stunning conclusion: seafloor spreading. New ocean floor is constantly created at mid-ocean ridges and moves away on both sides. This was the mechanism Wegener never knew about! Continents don't plow through the ocean floor - they ride along as the ocean floor moves. 🔍Detective Journal Entry #11: Connect all the evidence.

The Real Mechanism - Tectonic Plate

The magnetic stripes revealed the truth: Wegener was right about continents moving, but wrong about HOW. Scientists discovered that continents don't plow through the ocean floor. Instead, both the continents and ocean floor are broken into massive tectonic plates, rigid sections that include both the crust and a layer of the upper mantle. Continents are just passengers riding on these moving plates. 🔍Detective Journal Entry #12: Compare this mechanism to Wegener's original idea.

Case Closed

Detective Summary: How Earth Really Works The magnetic stripe evidence cracked the case! Earth's surface consists of moving tectonic plates that explain everything Wegener observed. The evidence trail: Continental fit ✓ Matching fossils ✓ Underwater mountains ✓ Magnetic stripes ✓ The missing mechanism: plate tectonics ✓ 🔍Detective Journal Entry #13: Record your final conclusions about how Earth works.

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Gondwana was a supercontinent that existed from about 550 million to 180 million years ago and included the landmasses that now make up South America, Africa, Australia, Antarctica, India, Madagascar, and Arabia.

Glacial striations are parallel grooves or scratches on bedrock caused by rocks and debris frozen into the base of a moving glacier that scrape against the underlying surface. These marks are powerful indicators of a glacier's past flow direction, helping geologists understand ancient glacial activity and climate.

Gondwana was a supercontinent that existed from about 550 million to 180 million years ago and included the landmasses that now make up South America, Africa, Australia, Antarctica, India, Madagascar, and Arabia.

Glacial striations are parallel grooves or scratches on bedrock caused by rocks and debris frozen into the base of a moving glacier that scrape against the underlying surface. These marks are powerful indicators of a glacier's past flow direction, helping geologists understand ancient glacial activity and climate.

Gondwana was a supercontinent that existed from about 550 million to 180 million years ago and included the landmasses that now make up South America, Africa, Australia, Antarctica, India, Madagascar, and Arabia.

Glacial striations are parallel grooves or scratches on bedrock caused by rocks and debris frozen into the base of a moving glacier that scrape against the underlying surface. These marks are powerful indicators of a glacier's past flow direction, helping geologists understand ancient glacial activity and climate.