Uni 1 Earth's Interior and Plate Tectonics

Continental Drift

the gradual movement of Earth's continents across the oceanic crust due to tectonic forces.

Continental Drift Evidence

1. Jig-saw fit

2. fossil evidence

3. rock types and structure

Paleomagnetism

the study of the Earth's ancient magnetic field recorded in rocks (alternating magnetic stripes on the ocean floor)

Polar Wandering

the apparent movement of Earth's magnetic poles over time, which is actually due to the shifting of the continents.

The continents have appeared to join…

200 million years ago

Plate

a section of the lithosphere that slowly moves over the asthenosphere, carrying pieces of continental and oceanic crust

Faults

fractures in Earth's crust along which movement has occurred, causing displacement of rock on either side

Continental Crust

• mostly granatic

• thick (10-70 km)

• buoyant (less dense than oceanic crust)

• mostly old

Oceanic Crust

• mostly basaltic

• thin (~7 km)

• dense (sinks under continental crust)

• young

As plates move, they create:

• earthquakes

• volcanoes

• mountain ranges

• deep ocean ranges

Convergent Boundary

boundary where two plates collide and come together

• density determines which plates come out on top

• subduction

• deep ocean trenches

• destructive

Subduction

where one tectonic plate is forced beneath another into the Earth's mantle, often causing volcanic activity and earthquakes

Deep Ocean Trenches

deep valley along the ocean floor beneath which oceanic crust slowly sinks toward the mantle

Convergent Oceanic-Oceanic

the one that is more dense will sink beneath the one that is less dense

• island arc-volcanoes

Convergent Oceanic-Continental

oceanic crust is more dense so it will sink below continental

• Mountains (Andes) and volcanoes can form-Volcanic Mountain Range

The Ring of Fire

horseshoe-shaped zone around the Pacific Ocean, known for its frequent earthquakes and volcanic eruptions, due to tectonic plate movements and subduction zones

Convergent Continental-Continental

neither is dense enough to sink into mantle

• mountains form and grow larger due to the colliding plates

• Ex. Hiamalayas

Divergent Boundaries

two plates slowly move away from each other

• In the ocean = Mid Ocean Ridge

• On land = Rift Valley

• earthquakes

• volcanoes

• constructive

Mid Ocean Ridge

underwater mountain ranges formed at divergent plate boundaries where new oceanic crust is created as tectonic plates spread apart

• seafloor spreading

Seafloor Spreading

where tectonic plates move apart at mid-ocean ridges, allowing molten material from the Earth's mantle to rise and create new oceanic crust

Rift Valley

a linear shaped lowland between several highlands or mountain ranges produced by the action of a geologic rift

• On land: characterized by steep-sided valleys with flat floors, often containing lakes or accumulating sediments

• Under the ocean: known as seafloor spreading, where new crust is created as plates diverge, and magma from the mantle flows out onto the ocean floor, forming mid-ocean ridges with rift valleys in the center.

Magnetic Stripes

symmetrical patterns of alternating magnetic polarities, formed by the Earth's magnetic field reversals during seafloor spreading at mid-ocean ridges

• Width of stripe indicates how long the pole was in the normal or reversed position

• The patterns are mirror images on either side

Transform Boundary

place where two plates slip past each other, moving in opposite directions

• shallow earthquakes

Hot Spots

large plume of hot mantle material rising from deep within the Earth. As tectonic plates move over a hotspot, volcanoes can form a chain, with the oldest volcanoes further away from the hotspot

Buoyancy

measure of the the upward force a fluid exerts on an object that is sumerged

Density

Density is the amount of matter (mass) compared to the amount of space (volume) the object occupies (mass/volume)

3 Main Layers of the Earth

• crust

• mantle

• core

Crust

outermost layer + thinnest layer

Composition: lighter elements like oxygen, silicon, aluminum, calcium, sodium, and potassium, forming rocks like granite and basalt

Mantle

located below the crust and the thickest layer

Composition: molten rock (magma), magnesium and silicon compounds

Core

located below the mantle, HOT 5000-6500 C, very dense, and high pressure

Composition: iron and nickles

Compositional (chemical) Layers

• Crust

• Mantle

• Core

Mechanical Layers

• lithosphere

• asthenosphere

• mesosphere

• outer core

• inner core

Lithsophere

• outermost layer

• rigid

• divided into tectonic plates

Asthenosphere

• most of the upper mantle

• composed of solid flowing rock

Lower Mantle

• strong, lower part of the mantle

• layer between asthenosphere and core

Outer Core

liquid iron and nickel spinning

Inner Core

• solid iron and nickel

• solid because of pressure (all of earth on top of it)

Layers of the Earth

Earthquakes

• Caused by plate tectonic stresses

• Located at plate boundaries

• Resulting in breakage of the Earth’s brittle crust

Focus

place deep within the Earth and along the fault where rupture occurs

Epicenter

geographic point on surface directly above focus

Seismic Waves

• produced by the release of energy

• move out in circles from the point of rupture (focus)

• 2 types: surface & body (travel inside & through earth’s layers)

P Waves

back and forth movement of rock; travel through solid/liquid/gas

S Waves

sideways movement of rock; travel through solids only

Surface Waves

circular movement of rock;

travel on surface – cause most damage!!

Love Waves

seismic wave that travel along the Earth's surface, causing the ground to move horizontally

Rayleigh Waves

seismic surface wave that cause both vertical and horizontal ground motion, resulting in a rolling, elliptical motion as they travel along the Earth's surface

Seismographs

record earthquake waves

The Driving Mechanism of Plates

Convection Currents

Heat Sources of Convection Currents

1. Heat Gradient and Gravity

2. Decay of Radioactive Materials

3. Core Heating of Mantle

4. Residual heat

Thermal Convection Flow in Mantle

• warm, less dense material rises

• coller, more dense material sinks

Slab-Pull

a force that drives plate tectonics, where a dense, cold oceanic plate sinks into the mantle at a subduction zone, pulling the rest of the plate along with it due to gravity

Ridge-Push

driving force in plate tectonics, where the elevated, hot lithosphere at mid-ocean ridges pushes the plates away, causing them to move

Volcanoes are Formed by:

• subduction

• rifting

• hot spots

Rifting

the process where the Earth's lithosphere stretches and thins, eventually leading to the formation of rift valleys