Techtonics

Proto-Earth

Early Earth before it separated into layers; described as a large, homogeneous blob.

Why did early Earth separate into layers?

Less-dense material moved outward while denser material sank toward the planet's center.

What are Earth's main internal layers?

Crust, mantle, outer core, and inner core.

Continental crust

Crust that is relatively thick, made of generally lighter material, and less dense/buoyant.

Oceanic crust

Crust that is relatively thin (about 10 km thick), relatively dense, and made largely of mafic minerals.

Which crust is thicker: continental or oceanic?

Continental crust.

Which crust is denser: continental or oceanic?

Oceanic crust.

Why does continental crust sit higher than oceanic crust?

Continental crust is less dense and therefore more buoyant.

Mafic minerals

Minerals relatively rich in magnesium and iron; they make up the denser oceanic crust.

Lithosphere

The crust plus the relatively cold uppermost mantle; although chemically different, they behave together as a rigid layer.

Lithospheric plates

Rigid pieces of lithosphere that move across Earth's surface.

Convergent plate boundary

A boundary where plates move toward one another.

What commonly happens at a convergent boundary involving a denser plate?

The denser plate is forced beneath the other plate in subduction.

Subduction

The process in which a denser tectonic plate sinks beneath another plate.

Divergent plate boundary

A boundary where plates move apart from each other.

What can eventually form at a divergent boundary?

A new ocean basin, as the plates separate and new crust forms.

Transform plate boundary

A boundary where two plates move side by side past one another.

Active coast

Also called a collisional or leading-edge coast; a coast located at a plate boundary.

What are common signs of an active coast?

Broken-up coasts, cliffs behind beaches, and offshore sea stacks/haystacks.

California coast

An example of an active/leading-edge coast.

Passive coast

Also called a trailing-edge coast; a coast with a smooth transition between continental and oceanic crust and no plate boundary at the coast.

South Carolina beaches

An example of a passive/trailing-edge coast.

Marginal coast

A coast near, but not directly on, a plate boundary; it may be protected by a plate boundary or island arc.

Thailand

A class example of a marginal coast.

What kind of coast is sheltered from the open ocean behind island arcs?

A marginal coast.

Continental or island arc coast

Collision/active coast associated with converging plates.

Neo-trailing, Amero-trailing, and Afro-trailing coasts

Examples of trailing-edge coast types associated with a new or mature ocean basin.

Slab pull

A force that helps move tectonic plates when a dense slab sinks into the mantle and gravitationally pulls the rest of the plate with it.

Paper-falling-off-a-table analogy

An analogy for slab pull: the part of the paper hanging over the edge pulls the rest downward.

What drives plate motion according to the notes?

The weight of dense slabs sinking into the mantle creates gravitational slab pull.

Evidence for plate tectonics

Fit of continents, matching rocks and mountain ranges, fossil evidence, glacial evidence, and continental magnetism.

Fit of continents

Observation that continents appear to fit together, supporting the idea that they were once connected.

When was the fit of continents first noted by cartographers?

1596.

Who later popularized the idea that continents fit together?

Francis Bacon.

Matching rocks and mountain ranges

Similar rock units and mountain belts on separate continents suggest those continents were once connected.

How do mountain belts support plate tectonics?

Matching mountain ranges across continents indicate the landmasses were previously joined.

Fossil evidence for plate tectonics

The same Triassic land-animal fossils are found on continents now separated by oceans.

Why are matching land-animal fossils on separate continents important?

Land animals could not easily cross modern oceans, so the continents were likely once connected.

Glacial evidence for plate tectonics

Glacial scratches and deposits suggest glaciers once spread outward from a common central polar region.

What do glacial scratches show?

They can reveal the direction glaciers moved and support former continental positions.

Continental magnetism

Magnetic evidence preserved in continental rocks that helps reconstruct past plate positions and magnetic-pole locations.

Geodynamo

The process in Earth's liquid outer core that generates the magnetic field.

What is Earth's liquid outer core mainly made of?

Iron and nickel.

What causes the outer-core geodynamo?

Convection in liquid iron and nickel caused by heat differences.

Earth's electromagnetic field

A magnetic field generated by convection in Earth's liquid outer core.

Aurora borealis

A natural light display caused when solar activity interacts with Earth's magnetic field and atmosphere.

Thermal remanent magnetization

Magnetism preserved in cooling rock as its minerals align with Earth's magnetic field.

Magnetic reversal

A change in which Earth's magnetic north and south poles switch positions.

Geologic time scale

A system used to organize Earth's history into major units of time.

Geologic time scale order, oldest to youngest

Precambrian, Paleozoic, Mesozoic, Cenozoic.

Precambrian

The oldest major division listed on the geologic time scale.

Paleozoic

The era after the Precambrian and before the Mesozoic.

Mesozoic

The era after the Paleozoic and before the Cenozoic.

Cenozoic

The most recent era listed on the geologic time scale.

Alfred Wegener

Scientist associated with continental drift; he integrated four of the five main continental observations.

Continental drift

The idea that continents move and were once connected in different positions.

Apparent Polar Wander Path (APWP)

A path that appears to show a magnetic pole moving over time; it is used as evidence that continents have moved.

When was APWP measured according to the notes?

1950.

Why was echo sounding originally developed?

In response to the Titanic disaster, to detect icebergs.

What did echo sounding become in the 1960s?

Precision sonar technology.

How did shipboard sonar contribute to plate tectonics?

It helped scientists image and map the seafloor.

Bathymetry

The measurement and mapping of the shape, depth, and topography of the seafloor.

Morphological profile

A cross-sectional shape/profile of the seafloor.

Paleomagnetism

Study of Earth's ancient magnetic field as recorded in rocks.

How is seafloor paleomagnetism different from continental paleomagnetism?

It is more symmetrical and has less overprinting.

Why is seafloor paleomagnetism more useful for identifying magnetic stripes?

New crust forms at the center and preserves a clearer, less-overprinted magnetic record.

Where does new oceanic crust form?

At the center line of a divergent boundary, such as a mid-ocean ridge.

What is the relationship between new crust and seafloor magnetic patterns?

New crust forms at the center, creating symmetrical magnetic patterns on both sides.

How often do magnetic reversals occur according to the notes?

About every 200-400 kyr (thousand years).

What does kyr mean?

Thousand years.

Age of oceanic plates

An important seafloor pattern used as evidence for plate tectonics; oceanic crust is youngest near where it forms and changes in age away from it.

Heat flow

Heat escaping from Earth; its distribution helps show tectonic activity and new crust formation.

Earthquake distributions

The global pattern of earthquakes, which outlines many plate boundaries.

Why are earthquake distributions evidence for plate tectonics?

Earthquakes cluster along plate boundaries, showing where plates interact.

Plates and volcanoes

The distribution of volcanoes is closely related to tectonic plate boundaries.

Why are volcano distributions evidence for plate tectonics?

Volcanoes commonly occur where plates converge or diverge, revealing plate-boundary activity.