Plate TectonicsEarth Systems

Caleb Oswalt

1st period

Wegner’s theory of Continental Drift

• Theory- the world was made up of a single continent through most of geologic time. That continent eventually separated and drifted apart, forming into the seven continents we have today.

Rejection

• Unbelievable • Insufficient Evidence• Wegner wasn't a Geologist• Didn’t answer “What force is causing the plates to move?”

Evidence

• Same plants and animals found across the world• Continents fit like a Jigsaw Puzzle

Supercontinent Theory

• Describes the constant Changing of Earth’s Crust.

*Pangaea- large supercontinent. *Panthalassa- ocean surrounding.

Supercontinent Theory

• Accretion is the process by which material is added to tectonic plates or a landmass.

• Rifting is a linear zone where the Earth's crust and lithosphere are being pulled apart

Effects of Plate Tectonics

• Plate tectonics causes a change in the ocean currents and in turn generates more heat. When tectonic plates shift, creation of the volcanic eruptions increases the degree of carbon dioxide (CO2) and sulfur dioxide (SO2) in the atmosphere. This is what leads to a rise in the temperature levels globally.

• On the a contrary, if the move is insignificant, the temperature levels record fall.

• A new dimension revealed by these studies also hints to the increased heat leading to a shift in the tectonic plates.

Effects of Plate Tectonics on Evolution

• Species evolved to adapt to their environments.

Whales have undeveloped legs, leading scientist to believe that they once walked

Giraffes developed long necks

Theory Of Plate Tectonics

• Describes large scale motion of Earth’s Lithosphere.

1. Lithosphere- Outermost shell.

2. Asthenosphere- Upper mantle of Earth.• Tectonic plates are able to move because the Earth's

lithosphere has a higher strength and lower density than the underlying asthenosphere

Movement

• Lateral density variations in the mantle result in convection.• Their movement is thought to be driven by a combination of

the motion of seafloor away from the spreading ridge and drag, downward suction, at the seduction zones.

• A different explanation lies in different forces generated by the rotation of the globe and tidal forces of the Sun and the Moon.

Types of Plate Boundaries

• Transform boundaries (Conservative) occur where plates slide or, perhaps more accurately, grind past each other along transform faults.

• Divergent boundaries (Constructive) occur where two plates slide apart from each other.

• Convergent boundaries (Destructive) occur where two plates slide towards each other commonly forming either a seduction zone (or a continental collision.

Picture Example

Isostatsy

• Refers to the state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density.

Isotactic Adjustments

• The rise of land masses that were depressed by the huge weight of ice sheets during the last glacial period.

Stress

• Is a measure of the internal forces acting within a deformable body.

Divergent Boundary

• Sea-floor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.

1. Red Sea-East African Rift, the Red Sea formed and is now part of the Sea.

Mid Ocean Ridge

• Is a general term for an underwater mountain system that consists of various mountain ranges (chains), typically having a valley known as a rift running along its spine.

Ex- Mid Atlantic Ridge

Divergent Boundary

• Pale magnetism is the study of the record of Earth’s magnetic field in rocks.

• Magnetic Reversals is a change in Earth’s magnetic field, like the magnetic north and the magnetic south are interchangeable.

• Magnetic Symmetry is a portion of the system whose properties and composition are homogenous and which is physically distinct from other parts of the system.

Normal Faults

• A planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of Earth movement.

• Rift valley of East Africa.

Convergent Boundary

• Seduction Zones is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle as the plates converge.

• Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins.

• The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which forms the continents and the areas of shallow seabed close to their shores, known as continental shelves. Plates come together.

Volcanoes

• Magma- liquid rock produced underneath the earths surface

Conditions in which magma forms

• 1st- temp of the rock rises above the melting point of the minerals the rock is composed of

• 2nd- pressure removed from the rock, the melting point of the rock decreases and rock will melt

• 3rd- the additions of fluids decreases the melting point even more and cause even more rock melting

Lava

• Lava- magma that flows onto Earths surface; the rock that forms when lava cools and solidifies

Volcano

• Common locations- common locations for volcanos usually are along the pacific Ring of Fire, or along the pacific coasts of North America

• Pacific Ring of Fire- one of the earths major earthquake zones

Pyroclastic Material

• Pyroclastic Material- fragments of rock that form due to volcanic eruption

• Viscosity- a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress

How does magma contents produce explosive eruptions?• Magma contents produce explosions because there are large

amounts of trapped gasses, water, and carbon gasses.

Types of Volcanoes

• Shield Volcanoes- Volcanic cones that are broad at the base and have gentle sloping sides. Covers wide area.

Types of Volcanoes

• Cinder Cones- Has very steep slopes, angles are close to 40’, have explosive eruptions and are made of pyroclastic material.

Types of Volcanoes

• Composite Volcanoes- made of alternating layers of hardened layers of lava, quite eruptions, then explosive eruptions.

Caldera

• Caldera- large, circular depression that forms when the magma chamber below the volcano empties and causes the ground to sink.

Oceanic + Oceanic

• Trenches- Some trenches are created as a result of erosion by rivers (which may have long since fallen dry), others are created by geological movement of tectonic plates, such as rift valleys or more commonly oceanic trenches.

Ex Mariana Trench

Seduction Zones

• Produce Volcanic Mountains, Continental + Continental

Collision Zones

• Continental + Continental • Fold mountains are

mountains formed mainly

by the effects of folding

on layers within the upper part of the Earth's crust.

Ex- Zagros Mountain

Collision Zones

• Plateaus- highland, consists of relatively flat terrain

Ex- Canyon lands National Park

Collision Zones

Ex. Himalayas• Compression refers to a set of stresses directed toward the

center of a rock.• Uplift -geological process most often caused by plate tectonics

which boosts elevation.

Transform Boundary

• Faults is planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement.

• Reverse fault is the exact opposite of Faults.• Strike-slip Faults, the fault surface is usually near

vertical and the footwall moves either left or right or laterally with very little vertical motion.

Transform Boundary

• Tension refers to a stress which stretches rocks in two opposite directions.

• Shear stress is the stress component parallel to a given surface, such as a fault plane, that results from forces applied parallel to the surface or from remote forces transmitted through the surrounding rock.

Earthquakes• Elastic rebound- the sudden rebound of elastically deformed

rock to its undeformed shape• Seismology- the study of earthquakes and seismic waves• Seismograph- instrument used to read vibrations in the

ground

Seismic waves

• Body waves- a seismic wave that travels through the body of the medium

• Surface waves- a seismic wave that travels along the surface of the earth has a stronger effect near the surface of the medium than on the interior

How does seismic waves lead to the determination of earth interior?• Seismic waves lead to the determination of earths interior

because seismic waves usually occur towards the center of the earth.

Earthquakes that happen away from active plate boundaries

• Not all earthquakes happen at plate boundaries some occur in the middle of continents others happen elsewhere

Seismic waves (count.)

• P waves- primary wave, or compression wave; a wave that causes particles of rock to move in a back and forth direction parallel to the direction its traveling

• S waves- secondary wave, seismic wave that causes the rock to move in a side to side motion perpendicular motion in which the wave is traveling

Magnitude• A measure of strength of an earthquake

Intensity

• the amount of damage cause by an earthquake• Mercalli Scale- uses roman numerals to show intensity by

numbers and describes the effects of the intensity.

Tsunami • A giant ocean wave that forms after a volcanic eruption,

submarine earthquake, or landslide.

Fault Block Mountain

• Ex- East African Rift Zone

Dome Mountains

• Are formed when the hot magma rises from the mantle and uplifts the overlying sedimentary layer of the Earth's crust.

Ex- Navajo Mountains in U.S.

Others

• Hot Spots- In geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere.

Ex Hawaiian Islands