Comprehensive Guide to Plate Tectonics and Continental Drift Evidence

Tectonics

The general term that refers to the deformation of Earth's crust and results in the formation of structural features such as mountains.

Alfred Wegener

A scientist best known for his hypothesis of continental drift.

Continental Drift

A hypothesis first proposed by Alfred Wegener in 1915, suggesting that continents were once joined in a supercontinent called Pangaea and began breaking apart about 200 million years ago.

Pangaea

The supercontinent that began breaking apart about 200 million years ago.

Evidence for Continental Drift

Fit of South America and Africa, matching fossils across the seas, matching rock types and structures, and ancient climates.

Main objection to Wegener's proposal

Its inability to provide a mechanism for continental drift.

Paleoclimatic evidence

Evidence supporting the idea of the late Paleozoic supercontinent in the Southern Hemisphere.

Lithified loess deposits

Deposits found in the deserts of Chile, Australia, and Africa that support the idea of the late Paleozoic supercontinent.

Tillites

Rocks formed by glaciers found in South Africa and South America that support the existence of Pangaea.

Cold water fossils

Fossils found in the deep-water sediments of the South Atlantic abyssal plain that support the idea of the late Paleozoic supercontinent.

Geometrical fit

The fit between South America and Africa proposed as evidence for the existence of Pangaea.

Precambrian rocks

Islands of Precambrian rocks along the Mid-Atlantic Ridge were never proposed as evidence supporting the existence of Pangaea.

Continental drift hypothesis rejection

The hypothesis was rejected primarily because Alfred Wegener could not provide a mechanism.

Frank Taylor

Proposed in 1910 that the continents were once joined.

Alfred Wegener's book

Published in 1922, it presented more evidence for continental drift than Frank Taylor's proposal.

Supercontinent

A large landmass formed by the joining of continents, such as Pangaea.

South America and Africa

Continents that fit together and share fossil evidence supporting the theory of continental drift.

Ancient climates

Climatic conditions from the past that provide evidence for continental drift.

Geological structures

Rock types and formations that match across continents, supporting the idea of continental drift.

Paleozoic

The era in which Pangaea existed before it began to break apart.

Continental drift hypothesis

The theory that continents have moved over geological time and were once connected.

Alfred Wegener's hypothesis

The hypothesis of continental drift proposed by Alfred Wegener.

Mechanism for continental drift

The explanation for how continents move, which was lacking in Wegener's proposal.

Geologic Similarities

Similar geological features found on different continents.

Mechanism of Continental Movement

A process that explains how continents move, which Wegener could not identify.

True or False: Continental Drift

To explain continental drift, Wegener proposed that the continents broke through the oceanic crust, much like ice breakers cut through ice.

Mesosaurs

An ancient reptile that lived in South America and Africa during the late Paleozoic.

Objections to Wegener's Hypothesis

Wegener's inability to provide an acceptable mechanism for continental drift.

Mid-Ocean Ridge System

A continuous mountain range on the ocean floor formed by tectonic plates.

Seismic Waves

Waves generated by earthquakes that travel through the Earth and can reflect and refract when encountering different materials.

Lithosphere

The rigid outer shell of the Earth, consisting of the crust and upper mantle.

Asthenosphere

The weak and plastic zone near the top of the mantle.

Earth's Core

The innermost layer of the Earth, consisting of a metallic solid inner core and a metallic liquid outer core.

Crust

The outermost layer of the Earth, which has the lowest density of all layers.

Plate Tectonics

The scientific theory that describes the large-scale movements of Earth's lithosphere.

Pacific Plate

The largest tectonic plate on Earth.

Oceanic Crust

The part of the Earth's crust that underlies the ocean basins.

Granitic Crust

The type of crust found in continental areas, which is less dense than oceanic crust.

Basaltic Lithosphere

The type of lithosphere that lies beneath the oceans.

Mapping the Ocean Floor

The process of creating modern maps showing the topography of both land and seafloor.

Trenches

Narrow, deep areas in the ocean that can reach depths of nearly 7 miles (11 km).

Earth's Structure

The layered composition of the Earth, including the core, mantle, and crust.

Rate of Movement

A measure of how fast tectonic plates move over time.

Direction of Movement

The path along which tectonic plates move.

Time for Continental Drift

The geological timeframe over which continental drift occurs.

Inner core

Solid, rotates faster than liquid outer core.

Earth's magnetic field

Believed to be the result of metallic ions in the outer core circulating as the planet rotates.

Importance of magnetic field

Helps shield the Earth from harmful radiation streaming from the Sun.

Geothermal gradient

25°C/km.

Heat sources of Earth

Heat from radioactive decay of uranium, thorium, and potassium, as well as friction and pressure.

Convection

Transfers heat within the Earth.

Formation of Earth's layers

Developed as molten iron and nickel sank to the core and lighter elements rose, forming the crust and mantle.

Elastic limit

Point where deformation becomes permanent.

Ductile materials

Deform permanently by flowing plastically.

Brittle materials

Fracture when deformed.

Surface rocks

Typically brittle and will fracture.

Buried rocks

Become ductile and deform plastically due to higher temperatures and pressures.

True or False: Lithosphere

The Lithosphere consists of both crustal rocks and a portion of the upper mantle.

True or False: Asthenosphere

Beneath Earth's lithosphere is the hotter and weaker zone known as the asthenosphere.

True or False: Thermal convection

The unequal distribution of heat inside Earth generates some type of thermal convection in the crust that ultimately drives plate motion.

Mid-oceanic ridges

Rising magma beneath generates earthquakes whose epicenters lie in a relatively narrow zone at the surface.

Ocean trenches

Epicenters near are spread over a wider area due to the way the subducting slab generates earthquakes in an inclined zone.

World-Wide Standardized Seismograph Network (WWSSN)

A global network of about 120 seismograph stations built in the 1960s that generated high quality seismic data.

Seismology

Became a quantitative science due to the data from WWSSN.

Focal mechanisms of earthquakes

Elucidated by the data from WWSSN.

Plate tectonic theory

Contributed to by the data from WWSSN.

Plates

Rigid slabs in the lithosphere.

Plate Boundaries

The regions where tectonic plates interact, including sliding past each other, overriding, tearing apart, or smashing into each other.

Lines of earthquake epicenters

Most effectively outline the edges of the lithospheric plates.

Continental Shelf

The seaward edge of the continents, best approximating their true outer boundary.

Major Plates

Earth's rigid outer shell consists of seven major plates.

Plastic Flowage

The deformation process that occurs in the asthenosphere, allowing it to flow.

Brittle Fracturing

The deformation process that occurs mainly in the lithosphere.

Basaltic Magma

Produced by partial melting of rising granitic plumes.

Energy Sources Driving Plate Motions

The export of heat from deep in the mantle to the top of the asthenosphere is thought to drive the lateral motions of Earth's lithospheric plates.

Seismic Activity

Most of Earth's seismic activity, volcanism, and mountain building occur along plate boundaries.

Gravitational Forces

The attractive forces of the Sun and Moon that influence plate movements.

Electrical and Magnetic Fields

Localized in the inner core, but not a primary driver of plate motions.

Swirling Movements

Movements of molten iron particles in the outer core, not a primary driver of plate motions.

Deep Mantle Heat Export

The process of heat moving from the deep mantle to the asthenosphere, driving plate tectonics.

Lines of magnetism

A concept related to the Earth's magnetic field.

Parallels of latitude

Imaginary lines that run parallel to the equator, used to measure distance north or south of the equator.

Random trends

Patterns or movements that do not follow a predictable or systematic path.

Hot spots

Areas in the mantle from which heat rises as a thermal plume from deep in the Earth.

Rigid slabs of lithosphere

The solid outer layer of the Earth, consisting of the crust and upper mantle.

Plate movement

The motion of tectonic plates due to mantle convection cells.

Ridge push mechanism

A process where gravity causes the elevated lithosphere at mid-ocean ridges to push down and away from the ridge.

Divergent plate boundaries

Boundaries where two plates move apart, leading to the formation of new seafloor.

Convergent plate boundaries

Boundaries where two plates collide, leading to mountain building or subduction.

Transform plate boundaries

Boundaries where two plates slide past each other, often causing earthquakes.

Ocean ridges

Underwater mountain ranges formed by plate tectonics.

Rift valleys

Low areas that form where tectonic plates are pulling apart.

Oceanic-oceanic island arc

An arc-shaped chain of islands formed by volcanic activity at a convergent boundary between two oceanic plates.

Oceanic-continental continental arc

Mountain ranges formed when an oceanic plate subducts beneath a continental plate.

Continental-continental mountain belt

Mountain ranges formed when two continental plates collide.

Intense earthquakes

Seismic events that occur at plate boundaries due to the movement of tectonic plates.

Linear valleys

Valleys that form along transform boundaries where two plates slide past each other.

Midoceanic ridge system

A continuous range of underwater volcanoes formed by divergent plate boundaries.

Basaltic rock

A type of volcanic rock that forms from the rapid cooling of basalt lava.

Great Rift Valley

A geological trench that runs from Lebanon to Mozambique, formed by divergent plate boundaries.