Earth Science Unit I: Continental Drift and Plate Tectonics

A set of 69 practice flashcards covering key concepts from the lecture notes on continental drift and plate tectonics.

What observation about coastlines supported Wegener's continental drift theory?

A continental fit—coastlines of continents match like pieces of a jigsaw puzzle.

Who proposed the theory of continental drift?

Alfred Wegener, a German meteorologist.

What did Wegener propose about the past arrangement of continents 300 million years ago?

All continents formed one supercontinent that gradually broke up and drifted apart.

What is the term for the single landmass Wegener called that included all present continents?

Pangaea (protocontinent).

What were the northern and southern parts of Pangaea called?

Laurasia (north) and Gondwanaland (south).

Where were Glossopteris fossils first found?

Gondwana region, northern India.

What was Panthalassa?

The single global ocean that surrounded Pangaea.

Why do some geologists think land bridges may have connected today’s continents?

Similar fossils found in India, South America, Southern Africa, Australia, and Antarctica.

Describe Glossopteris.

Extinct seed fern with tongue-shaped leaves; about 4 m tall; dominant plant of Gondwana.

Where were Mesosaurus fossils found?

South Africa and South America.

Where have Cynognathus fossils been found?

Africa and Argentina (South America).

Where is Lystrosaurus found?

India, Antarctica, and Africa.

What does 'Aclimate mismatch' refer to?

Fossils of tropical plants in coal deposits in cold polar regions; suggests past warmth and continental drift.

What does glacial evidence on continents include?

Glacial grooves and marks carved into bedrock; grooves found on continents now near the equator.

What are striations?

Grooves formed by the scraping of creeping glaciers.

What rock evidence supports continental drift?

Identical rocks of the same type and age on opposite sides of the Atlantic; similar rock strata in South Africa and Brazil.

What is orogeny?

Birth and formation of mountain ranges.

What mountain-range evidence supports continental drift?

Similar rock types, ages, and structures on mountain ranges across the Atlantic (e.g., Appalachian–Greenland–Ireland–Scotland–Norway similarities).

What does 'mountain building' refer to?

Formation of mountains due to collision or compression between continents.

How were the Himalayas formed?

By the collision of the Indian plate with the Asian continent.

What is Permanentism?

The theory that continents and ocean basins have always been permanent features on Earth.

What is a driving mechanism in Wegener's theory?

A process that could generate forces strong enough to move the continents, causing drift.

What is centrifugal force in this context?

Center-fleeing force; Wegener believed Earth's rotation produced a force toward the equator.

What is pole-fleeing force?

Term Wegener used to refer to the centrifugal force due to Earth's rotation.

What about gravitational forces in continental drift?

The sun and moon exert gravitational forces on Earth, but calculations show they are not strong enough to move continents.

What does SONAR stand for and what does it do?

Sound Navigation and Ranging; emits sound waves and detects reflections to locate objects underwater.

What is echo sounding?

A method of calculating distances and ocean depths using speed of sound and echo time.

What frequency range do SONAR waves operate in?

Ultrasonic waves above the audible range.

What are pings?

Signals that reflect from objects and are detected by instruments.

What is a continental shelf?

The area of seabed near a continent where the sea is shallow; geologically part of the continental crust.

What is a continental slope?

The slope dropping from the edge of the continental shelf to the deep ocean floor.

What is a mid-ocean ridge?

An elevated region with a central valley on the ocean floor at the boundary between two diverging tectonic plates; new crust forms from upwelling magma.

What is an abyssal plain?

A very large, flat sediment-covered area of the ocean floor.

What is a seamount?

An underwater mountain rising above the deep seafloor; may become an island.

What is a guyot?

A flat-topped seamount totally underwater.

What is an ocean trench?

A long, narrow, deep depression on the ocean floor, usually parallel to a plate boundary, formed where one plate subducts.

What is a magnetic anomaly?

Higher than normal magnetic activity due to magnetic materials such as iron.

What are seafloor stripes?

Strips of ocean floor that exhibit different magnetic or age characteristics.

What are magnetic reversals?

Reversals in the orientation of Earth's magnetic poles, sometimes coinciding with geographic poles and other times opposite.

What are ferromagnetic materials?

Materials that contain considerable amounts of iron capable of magnetic interactions.

What did Harry Hess propose?

Seafloor spreading; mantle convection causes the seafloor to spread sideways, creating magnetic and age patterns.

What does symmetrical seafloor pattern mean?

The age and magnetic patterns on one side of a ridge mirror those on the other side.

What is a plate?

A large, thick, rigid slab of solid rock; a broken piece of the crust.

What does tectonics mean?

From Greek tekton, meaning builder; Earth’s surface is built by plates.

Name the seven major tectonic plates.

North American, South American, Eurasian, African, Indo-Australian, Pacific, and Antarctic.

What are microplates?

Smaller plates such as the Juan de Fuca, Cocos, Nazca, Scotia, and Philippine plates.

What is mantle convection?

The main driving mechanism that generates forces strong enough to move the plates.

What is a divergent plate boundary?

Where new crust is created as the plates move away from each other.

What is a convergent plate boundary?

Where crust is destroyed and one of the plates sinks into the Earth’s interior.

What is a transform plate boundary?

Where the crust neither creates nor destroys as plates slide horizontally past each other.

What are mid-ocean ridges?

Cracks and gaps between diverging plates filled with molten rock forming new oceanic lithosphere.

What is an example of a young ocean basin?

The Red Sea, formed by the divergence of the Arabian Peninsula and Africa.

What are deep trenches?

Deep depressions at subduction zones; deepest parts of the ocean floor and geologically active.

What happens when the subducting plate is beyond 100 km deep into the mantle?

Water and gases are released, causing magma melting and volcanic activity at the surface.

What happens when two continental plates collide?

Edges buckle or crumple to form mountain ranges.

When did the Himalayas form and why?

About 55 million years ago, due to the collision of the Eurasian and Indo-Australian plates.

What is Mt Everest's height?

8,848 meters above sea level.

In a convergence involving two oceanic plates, which plate sinks first?

The colder and older plate, due to higher density.

What is an island arc?

A curved chain of volcanic mountains above a subduction zone that can become islands.

Which archipelago is an example of an island arc?

The Philippine Archipelago.

What is the San Andreas fault an example of?

A transform plate boundary on land.

What occurs at transform plate boundaries?

Plates slide horizontally past each other with neither creation nor destruction of crust.

What are hot spot volcanoes?

Volcanoes formed above an anomalously hot spot in the mantle where magma rises in plumes.

What happens at divergent boundaries regarding crust?

New crust is created as plates move apart.

What happens at convergent boundaries regarding crust?

Crust is destroyed as plates collide and one sinks.

What is the Wilson Cycle?

The opening and closing of ocean basins through the opening and closing of basins.

What is plate tectonics?

A theory that explains Earth's constantly changing surface in terms of moving plates.

Name the seven major plates again.

North American, South American, Eurasian, African, Indo-Australian, Pacific, and Antarctic.

What are microplates? (restate)

Smaller plates such as Juan de Fuca, Cocos, Nazca, Scotia, and Philippine.

What do you call the process that moves the plates?

Mantle convection as the driving mechanism.

What is the main driving mechanism for plate movement?

Mantle convection moving the crustal plates.

Where are the three main types of plate boundaries located?

Divergent (away), convergent (tushing together), and transform (sliding past).

What region is used as an example of a divergent boundary creating new ocean floor?

Mid-ocean ridges where magma forms new lithosphere.

What major oceanographic feature is formed by subduction and is parallel to plate boundaries?

Ocean trenches.

What is a key feature of the seafloor ages relative to distance from the central ridge?

Rocks closest to the central ridge are the youngest; age increases with distance.

What did Arthur Holmes propose in 1929?

Convection currents of liquid materials in Earth's interior pushed and moved the continents.

Where are the seven major plates located geographically?

Across the major continents and oceans: North America, South America, Eurasia, Africa, Indo-Australia, Pacific, Antarctic.

What is the term for rocks that were formed in the same location but are now separated by sea-floor spreading?

Identical rocks on opposite sides of the Atlantic with matching age/structure.

What evidence links Earth's past climates to continental drift besides fossils?

Glacial evidence, coal deposits in polar regions, and tropical plant fossils.

Why is Panthalassa significant in Wegener's theory?

It was the vast ocean surrounding Pangaea, illustrating the extensive ocean basins that existed.

Which mountain range did Wegener believe was once a single range before the drift?

Appalachians (in North America) were part of a larger mountain range with Greenland, Ireland, Scotland, and Norway.