Evidences of Plate Movement – Lecture 1.5

Vocabulary flashcards summarizing major terms, people, and evidences supporting plate movement, continental drift, seafloor spreading, magnetic reversal, and hotspot theories.

Modern unifying theory explaining the movement and interaction of Earth’s lithospheric plates driven by mantle convection, ridge push, and slab pull.

Plate Tectonics

Alfred Wegener’s 1912 idea that continents were once joined in a supercontinent and have since moved apart.

Continental Drift Theory

The single large landmass that existed about 250 million years ago; means “All Earth” in Greek.

Pangaea

Northern supercontinent formed when Pangaea split; included North America, Europe, and Asia.

Laurasia

Southern supercontinent formed from Pangaea; included South America, Africa, India, Australia, and Antarctica.

Gondwanaland

German meteorologist who proposed the Continental Drift Theory.

Alfred Wegener

Matching coastlines—e.g., South America and Africa—suggest continents once fit together.

Evidence from Shapes

Similar rock layers and aligned mountain ranges (e.g., Appalachians and UK mountains) found on separate continents.

Evidence from Rocks and Mountains

Identical plant and animal fossils discovered on widely separated continents, supporting former connection.

Fossil Evidence

Fresh-water reptile fossil found in South America and Africa, indicating the continents were once joined.

Mesosaurus

Ancient fern fossil found on multiple southern continents, supporting Gondwanaland’s existence.

Glossopteris

Triassic land reptile whose fossils on different continents support continental drift.

Cynognathus

Triassic herbivorous reptile fossil distributed across Africa, India, and Antarctica, evidencing past land connection.

Lystrosaurus

Rock deposit left by ancient glaciers; identical tillites on several continents show they were once near the pole.

Tillite

Matching glacial deposits and striations across now-distant continents indicate past united landmasses.

Glaciation Evidence

Coal beds in Antarctica imply the continent was once near the equator where lush vegetation thrived.

Coal Deposits Evidence

Harry Hess’s 1962 proposal that new oceanic crust forms at mid-ocean ridges and moves outward, widening ocean basins.

Seafloor Spreading Theory

American geologist who, with Robert Dietz, proposed the Seafloor Spreading Theory.

Harry Hess

Undersea mountain chain where magma rises, forming new oceanic crust and causing seafloor spreading.

Mid-Ocean Ridge

Periodic flip of Earth’s magnetic poles recorded in ocean-floor basalt as symmetrical magnetic stripes.

Magnetic Reversal

Iron-rich mineral in basalt that aligns with Earth’s magnetic field during cooling, preserving magnetic history.

Magnetite

Stationary mantle plume that melts overlying lithosphere, forming volcanic chains like the Hawaiian Islands.

Hotspot

Column of hot, buoyant mantle rock rising from deep within Earth, feeding hotspot volcanism.

Mantle Plume

Linear series of volcanic islands created as the Pacific Plate moves over a hotspot.

Hawaiian Island Chain

Circular flow of hot, less-dense mantle material rising and cool, denser material sinking, driving plate motion.

Convection Currents

Gravity-driven force where elevated mid-ocean ridges push oceanic plates away from the ridge crest.

Ridge Push

Force generated as a dense, subducting plate sinks into the mantle, pulling the trailing lithosphere with it.

Slab Pull

Oceanic crust is youngest at mid-ocean ridges and becomes progressively older away from them.

Age Pattern of Oceanic Rocks

Marine sediments are thinnest at mid-ocean ridges and thicken with distance, supporting seafloor spreading.

Sediment Thickness Pattern

Use of sound waves and submersibles to map the ocean floor, revealing mid-ocean ridges and deep-sea trenches.

Sonar Mapping