The Ocean Floor

Warm-up: August 12, 2013 Write down the following Questions 1. List and Describe the 3 Layers of the earth 2. List 4 Characteristics of Oceanic Crust 3. List 4 Characteristics of Continental Crust 4. What is Continental Drift? 5. How is plate tectonics and convection cells associated with contental drift? 6. How was the Mid-Ocean Ridge formed? 7. How are trenches formed?

The Water Planet

Density Soda Demo Draw Sections of the Earth and Label

Core Innermost layer Composed of Iron Under a lot of pressure 4,000ºC Composed of a solid inner core and a liquid outer core Core gives us our magnetic field.

Mantle Middle Layer Very, very hot – near the melting point of rocks. Acts like a liquid and flows very slowly although most of it is solid. It swirls and mixes.

Crust Outermost layer Composed of Solid plates Very thin

Compass

There are two types of crust 1. Oceanic Crust ~8 km (3-5 miles) thick 2. Continental Crust ~ 32 km (25 miles) thick

Crust The oceanic crust is made up of basalt. The continental crust is made up of granite.

Crust Oceanic Crust Basalt More dense/Sinks Darker Color Thinner 200 million years old/ younger Composed mostly of Fe and Mg Continental Crust Granite Less dense/Floats Lighter color Thicker 3.8 billion years old/ older Composed mostly of Salts: Na, K, Ca, Al

String Demo Color Plate Sheet

Sir Francis Bacon 1620 he suggested that the edges of some of the continents fit together like puzzle pieces.

Cut and Paste Diagram

Alfred Wegener 1912: proposed continental drift All the continents were once joined as one big super-continent called Pangaea. Pangaea began to break up ~180 million years ago.

Little problem! Scientists didn’t like this idea because they couldn’t explain how the continents could move. What would cause it to move? Boiling Water Student Demo What would cause it to move? In the 1950’s and 1960’s scientists determined that the continents move because of plate tectonics.

Plates move The movement of large plates on the earth’s crust is due to convection cells. Draw and label a convection cell

Convection Cells

Mid-Ocean Ridges A series of underwater volcanic mountains which are created due to plates moving apart.

Look at the map. Where do ridges occur? Label

Mid-ocean Ridge System Where do you think a mid-ocean ridge is occuring. It includes the: –Mid-Atlantic Ridge: middle of the Atlantic –East Pacific Rise: the main section of ridge in the Eastern pacific

Mid-Ocean Ridges

Mid-Atlantic Ridge

East-Pacific Rise

Scientists were very curious as to how the ridges were formed and studied them intensively.

Sea-floor Spreading 1.The mantle move due to convection cells 2.Hot magma is pushed up between the plates 3.The magma moves UP and OUT 4.The magma cools creating new sea floor.

Evidence: Label Diagram 1.Sea floor closest to the ridge is younger than rocks farther away. 2.Magnetic bands occur on the sea floor called magnetic anomalies. As new rock is laid down it keeps the magnetic orientation of the Earth when it was laid

Mid-Ocean Ridge System This made sense because it was known that the earth’s magnetic field reverses itself every few million years. As new rock is laid down the particles in the rock would keep the magnetic orientation of the Earth when it was laid down.

Mid-Ocean Ridge System The resulting bands are called magnetic anomalies and show that the sea floor is constantly changing.

Mid-Ocean Ridge System RECAP: At the mid-ocean ridges, pieces of oceanic crust are separating and releasing material in a crack called a rift. Material from the mantle is released and forms new ocean floor. This process is called sea-floor spreading.

What else can happen between plates?

Just as there are ridges in the ocean there are also trenches.

Trenches These are formed when two plates collide. Created due to the process of subduction One plate dips below the other and sinks into the mantle. the trenches can also be called subduction zones.

Draw diagram of how a trench is formed

Look at diagram: Where can they have formed Label Ex. Peru-Chile Trench Mariana Trench

Ocean Floor Mid-Ocean Ridges Occurs when Two Oceanic Crusts Separate Due to the process of Sea Floor Spreading Ex. Mid-Atlantic Ridge Eastern Pacific Ridge Trenches (aka Subduction Zones) Occurs when Two Oceanic Crusts Collide Due to the process of Subduction Ex. Peru-Chile Trench Mariana Trench