Continental Drift Evidence

Why This Matters

Continental drift isn't just a historical curiosity—it's the foundation for understanding plate tectonics, one of the most tested concepts in geophysics. When you encounter questions about earthquake distribution, mountain building, or even climate change over geological time, you're really being asked to demonstrate your understanding of how and why continents move. The evidence for continental drift spans multiple disciplines: paleontology, geomagnetism, stratigraphy, and structural geology—and exam questions love to test whether you can connect these different lines of evidence.

The key insight here is that Alfred Wegener's hypothesis was rejected for decades not because the evidence was weak, but because he couldn't explain the mechanism. Today, we understand that seafloor spreading and mantle convection drive plate motion. As you study these ten types of evidence, don't just memorize what each one shows—understand why it supports continental drift and how it connects to modern plate tectonic theory. That's what separates a 3 from a 5.

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Geometric and Structural Evidence

These lines of evidence focus on the physical fit and geological continuity between continents—the most intuitive arguments for a once-connected supercontinent. When landmasses separate, they leave behind matching edges and truncated geological features like torn pieces of a photograph.

Jigsaw Fit of Continents

• The continental shelf edges of South America and Africa align with less than 1° of error—this fit is even more precise than the visible coastlines suggest
• Coastline matching was Wegener's original observation in 1912, though critics dismissed it as coincidence until other evidence accumulated
• Computer reconstructions of Pangaea use this geometric fit as the starting framework, confirming the visual match with quantitative precision

Mountain Belt Continuity

• The Appalachian Mountains continue as the Caledonian Mountains in Scotland, Ireland, and Scandinavia—same rock types, same deformation age (~400 Ma)
• Structural trends including fold orientations and fault patterns align perfectly when continents are reassembled
• Orogenic belts that appear truncated at coastlines provide powerful evidence that continental margins were once connected interior regions

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Paleontological Evidence

Fossil distributions reveal biological connections between now-separated continents. Organisms can't swim across thousands of kilometers of ocean, so matching fossils on different continents indicate those landmasses were once joined.

Fossil Evidence

• Mesosaurus, a freshwater reptile, appears only in Brazil and South Africa—it couldn't have crossed the Atlantic
• Glossopteris, a seed fern, is found across South America, Africa, India, Antarctica, and Australia—defining the extent of Gondwana
• Cynognathus and Lystrosaurus (land reptiles) show similar distributions, ruling out explanations involving land bridges across deep oceans

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Paleoclimate Evidence

Climate indicators preserved in rocks reveal that continents have migrated through different climate zones over geological time. A glacier can't form in the tropics, and coal swamps can't exist in polar regions—so these deposits tell us where continents used to be.

Paleoclimate Indicators

• Coal deposits in Antarctica and Spitsbergen indicate these now-frozen regions once supported lush tropical vegetation
• Evaporite deposits (salt, gypsum) in northern Europe suggest these areas were once in arid subtropical zones near 30° latitude
• Climate-sensitive sediments provide latitude constraints independent of other evidence types, strengthening the overall reconstruction

Glacial Deposits and Striations

• Tillites (lithified glacial deposits) of Carboniferous-Permian age occur in South America, Africa, India, and Australia—all near the equator today
• Glacial striations show ice flow directions that only make sense when continents are reassembled around a South Polar ice cap
• The Dwyka Tillite in South Africa matches correlative deposits in Brazil, with striations pointing toward a common glacial center in reconstructed Gondwana

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Geological Correlation Evidence

Matching rock types and ages across ocean basins demonstrate that separated continents share a common geological history. Rocks don't lie—identical formations of the same age on different continents must have formed together.

Rock Type and Age Correlations

• Precambrian cratons in Brazil and West Africa show identical rock sequences, metamorphic grades, and radiometric ages (~2.0 Ga)
• The Brasília-Damara orogenic belt continues from South America into Africa with matching structural styles and timing
• Isotopic signatures in basement rocks provide geochemical fingerprints that match across the Atlantic, independent of visual correlation

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Geomagnetic Evidence

Paleomagnetic data record the ancient orientation and intensity of Earth's magnetic field, providing quantitative constraints on past continental positions. Magnetic minerals act like tiny compasses frozen in rock, preserving the field direction at the time of formation.

Paleomagnetism

• Apparent polar wander paths differ for each continent but converge when continents are reassembled—proving the continents moved, not the poles
• Magnetic inclination indicates paleolatitude: horizontal for equatorial positions, vertical for polar positions
• Remanent magnetization in rocks as old as 3 Ga allows reconstruction of continental positions through deep time

Seafloor Spreading

• Symmetric magnetic stripes on either side of mid-ocean ridges record periodic geomagnetic reversals as new crust forms and spreads
• Vine-Matthews-Morley hypothesis (1963) explained these stripes and provided the mechanism Wegener lacked
• Spreading rates calculated from stripe widths and reversal chronology range from $\sim$2 cm/yr (Atlantic) to $\sim$15 cm/yr (East Pacific Rise)

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Active Tectonic Evidence

Modern geological activity marks plate boundaries and demonstrates that continental drift is an ongoing process. Earthquakes, volcanoes, and hotspot tracks show that plates are moving right now—continental drift isn't just ancient history.

Plate Boundary Earthquakes and Volcanoes

• Seismicity concentrates along narrow belts that define plate boundaries—the "Ring of Fire" outlines the Pacific Plate
• Earthquake focal mechanisms reveal the direction and type of plate motion (convergent, divergent, or transform)
• Volcanic arc distribution correlates with subduction zones, where oceanic lithosphere descends beneath overriding plates

Hotspot Tracks

• The Hawaiian-Emperor seamount chain shows progressive age increase from Hawaii (active) to Meiji Seamount (~82 Ma), tracking Pacific Plate motion
• The 47 Ma bend in the chain records a major change in Pacific Plate motion direction
• Hotspot reference frames allow calculation of absolute plate velocities, not just relative motion between plates

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Quick Reference Table

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Self-Check Questions

1. Which two types of evidence both demonstrate geometric matching between continents, and how do they differ in what they prove?

2. If an FRQ asks you to explain why Wegener's hypothesis was initially rejected, which piece of evidence would you cite as the key discovery that later provided the missing mechanism?

3. Compare and contrast how paleoclimate indicators (coal deposits vs. glacial tillites) constrain ancient continental positions differently.

4. A student claims that Mesosaurus fossils prove all the southern continents were once connected. Why is this incorrect, and which fossil provides better evidence for the full extent of Gondwana?

5. How do apparent polar wander paths and hotspot tracks both provide evidence for continental motion, and what does each method uniquely reveal that the other cannot?