Unit 4: How do the oceans change? What are the parts of the oceans?

Parts of the Earth The Earth is divided into 3 zones: Atmosphere: The air above the Earth Hydrosphere- All the water on the surface of the Earth along with the clouds Lithosphere- The solid surface of the Earth

How does the Lithosphere change? TECTONICS!

Tectonics and the Oceans The changing of the oceans is due to plate tectonics

https://www.youtube.com/watch?v=UwWWuttntio

What is Plate Tectonics? A theory that states how the Earth’s rigid crust (lithosphere) is divided into approximately 21 plates that can interact with each other through sliding on the asthenosphere The asthenosphere is part of the upper mantle where the rocks are partially molten and not rigid These plates are moving carrying the continents and islands with them

What is the difference between continents and ocean?

Types of Crust Oceanic Crust Continental Crust Originally formed at mid-ocean ridges Ranges from 5-10km thick Predominately consists of Basalt Density is 2.9g/cm^3 Continental Crust Average thickness of 35km Predominately silicate materials (granite) Density is 2.7 g/cm^3 Which is significantly lower than that of oceanic crust

How do you build crust? Magma=Melted Rock When the rocks hardens it becomes crust The type of magma, how deep it hardens and how fast it hardens determines what crust it will become!

Isostasy A condition of equilibrium in the lithosphere, where any change in the mass of one part will be off set by a change in the mass of another part A volcano builds continental crust  Erosion causes continental crust to lose sediment  Crust gets less dense and rises  Sediments are deposited and create a geosyncline  Geosyncline becomes more dense and sinks

How do the Plates in the lithosphere move? Convection Currents Currents in the mantle are thought to be responsible for the movement of the lithospheric plates Movement of heat in mantle due to differences in density Hot magma becomes less dense and rises  Cools and becomes more dense and sinks

https://www.youtube.com/watch?v=ryrXAGY1dmE https://www.youtube.com/watch?v=RA2-Vc4PIOY

Evidence Indicating Plate Boundaries Zones of Volcanic and Earthquake Activity Ex: West Coast of N. and S. America and the East Coast of Asia Rift Zones A valley that forms when rock along a fault is pulled apart, it is found in the middle of the ridge Ex: Mid-Atlantic Ridge Fault Zones Produced as the result of movement of rock along either side of a crack in the Earth’s crust Ex: San Andreas Fault in California

Types of Plate Boundaries Overview https://www.youtube.com/watch?v=Wp-hZ0QCoQY

Types of Plate Boundaries 1. Divergent Plate Boundary Where plates move apart Geologic Features Found Here: Rift Valley Volcanoes Earthquakes Mountains (Ridge) Examples: Mid-Atlantic Ridge East Pacific Rise

Divergent Plates-What’s in the middle? Rift Valleys (Diverging Boundaries) A valley that is created where two plates are moving apart from one another An example of this is the Mid- Ocean Ridge and East African Rift Valley

Mid-Atlantic Ridge

What happens at the ridge? SEA FLOOR SPREADING!

Sea Floor Spreading Sea Floor Spreading Theory Mid Ocean Ridge The ocean floors are spreading apart as new rock material is added to the crust in the regions of mid-ocean ridges Mid Ocean Ridge Mountain chain running along the middle of an ocean basin Strip of igneous rock parallel to the ocean ridges shows reversal of magnetic orientation This provides evidence of sea floor spreading

https://www.youtube.com/watch?v=bGye6vlOpbY

Where’s the Evidence? Age of Igneous Rock on Ocean Floor The sea floor is younger at the ridges and gets older as you move towards the continents Reversal of Magnetic Polarity Igneous rocks at the mid-ocean ridge show magnetic orientation of Earth’s magnetic poles when the rock solidifies

Magnetic Polarity Normal Polarity Reverse Polarity The compass needle would point to north This is the magnetic orientation of Earth today Reverse Polarity The compass needle would point to south Not today’s magnetic field, but has occurred in the past many times

https://www.youtube.com/watch?v=I6Ggs7nUjxA

Continental Drift – Seafloor Spreading Connection!! Alfred Wegener’s missing evidence: Seafloor spreading explains how the continents move The continents are on plates, which move over the asthenosphere

https://www.youtube.com/watch?v=3dZuvNorPtg

2. Convergent Plate Boundary Where plates move towards each other Oceanic – Continental Oceanic – Oceanic Continental – Continental Geologic Features and Activities Found Here: Mountains On Continents Volcanoes Earthquakes Trench Deepest part of the ocean Subduction Zone Example: Tonga Trench

Subduction Zones The area where two plates collide together (Converge) and one of the plates (Subducting Plate) is forced down into the mantle where it will be destroyed Subducting Plate The plate this is being forced down

https://www.youtube.com/watch?v=e6U198ULMYo

What forms a subduction zone? 2. Converging Boundaries Oceanic – Continental The heavier, more dense, oceanic crust will be forced down (subducted) into the mantle where it will be destroyed Earthquakes, deep trenches, and volcanic islands are created An example of this is Japan

Oceanic – Continental

Example of Japan

Deepest Place on Earth https://www.youtube.com/watch?v=ypvNe_oXEXc https://www.youtube.com/watch?v=43xSnOdij3s https://www.youtube.com/watch?v=A_038g_1JT0

Continental – Continental OR Oceanic – Oceanic When two of the same type of plates collides with one another and the more dense of the two is forced down (subducted) into the mantle where it will be destroyed A lot of earthquake and mountain building occurs at these boundaries An example of this is India converging with Asia which forms the Himalayan Mountains

Oceanic – Oceanic

Continental – Continental

Himalayan Mountains

Why is Everest so tall? https://www.youtube.com/watch?v=uy9GFAOGGXU

Transform (Sliding) Boundaries Where plates slide past one another Geologic Activity Found Here: Earthquakes Example: San Andreas Fault

San Andreas Fault

https://www.youtube.com/watch?v=ZxPTLmg0ZCw

Hot Spots Areas of Volcanic Activity in the middle of lithospheric plates The hot spot does not move!!! The plates move over the hot spot Ex: Hawaii THIS IS NOT A FAULT!!!

Ocean Floor Structures

How is it all connected? The movement of tectonic plates creates the shape of the oceans we know today Different plate boundaries creates different plate structures

Mapping the Seafloor Features Bathymetry – the study and mapping of seafloor elevations. Techniques Early explorers measured depth using rope; results were often inaccurate. Echo Sounder (SONAR) determines depth by measuring the time required for sound to leave a ship, reflect off the sea floor and return to the ship.

Mapping the Seafloor Features Techniques continued Multibeam sonar systems take several soundings at a time. This is a faster method. Satellites can measure very large scale sea floor features by determining changes in sea surface elevations.

Bathymetry: History and Uses https://www.youtube.com/watch?v=K8blL9Ki2mQ https://www.youtube.com/watch?v=46IOh3EZT4c https://www.youtube.com/watch?v=WLBQ-rAb-24

Deep Seafloor Features Continental Shelf: closest to coastline; nearly flat borders on the edge of the continents that slope toward ocean basins. Continental Slope – steep slope extending to the seafloor. Continental Rise – gentle slop formed at the base of the slope due to accumulation of eroded sediments.

Abyssal Plain – vast plain extending seaward from the base of the continental slope Oceanic Ridge – underwater mountain range typically having a valley (rift) running along its spine. Rift Valley – valley formed from the spreading apart of seafloor at oceanic ridges

How does heat near the rift affect elevation? Heat Flow A measurement of the amount of heat leaving the rocks of the lithosphere Heat Flow values are high in the areas of rift where magma is rising Heat Flow values decrease as you move away from the rift The elevation at the rift is higher because the rocks expand due to high temperatures Elevation decreases as you move away from the rift because rocks cool and contract

Guyot – flat topped sea mounts caused by erosion Seamount – steep sided volcanoes rising abruptly, sometimes piercing the sea surface (island formation). Guyot – flat topped sea mounts caused by erosion

Trench – a long, narrow depression on the ocean floor with relatively steep sides. Deepest part of the ocean. Tectonic plate boundaries converging; subduction cause mountain ranges.

Under water Volcano – a volcano not located on an oceanic ridge. Islands – body of land surrounded by water. Can be formed by: Deposition of sediments An underwater volcano can rise above sea level.

Deep Seafloor Profile