Chapter Two The Sea Floor Geography of the Ocean Basins Why is it important to study geography of the ocean basins in marine biology? Why is it important to study geography of the ocean basins in marine biology? Natural environments Formation of shoreline Determine the depths Control sediment at bottom: sand, mud, rocks Create new islands and undersea mountains Galapagos Islands Geography of the Ocean Basins The world ocean is the predominant feature on the Earth in total area: The world ocean is the predominant feature on the Earth in total area: In the Northern Hemisphere, 61% of the total area is ocean. In the Southern Hemisphere, about 80% of the total area is ocean. Geography of the Ocean Basins The world ocean is divided into four large basins: Pacific, Atlantic, Indian and Arctic. The world ocean is divided into four large basins: Pacific, Atlantic, Indian and Arctic. Geography of the Ocean Basins Are the Pacific, Atlantic, Indian and Arctic oceans interconnected? Are the Pacific, Atlantic, Indian and Arctic oceans interconnected? How did the Earth Form? How did the Earth Form? Scientists refer to this interconnected system as the World Ocean Formation of the Earth The Earth is thought to have originated 4.5 billion years ago from dust accumulated from the Big Bang The Earth is thought to have originated 4.5 billion years ago from dust accumulated from the Big Bang Due to heat associated with these events, the early Earth was likely molten Due to heat associated with these events, the early Earth was likely molten This allowed materials to settle by density as the materials cooled This allowed materials to settle by density as the materials cooled Structure of the Earth Heavier materials settled deep in the Earth Heavier materials settled deep in the Earth Lighter components formed a thin crust Lighter components formed a thin crust Eventually, the Earths oceans and atmosphere began to form Eventually, the Earths oceans and atmosphere began to form Earths location relative to the sun allows for water to stay liquid an essential element to sustain life Earths location relative to the sun allows for water to stay liquid an essential element to sustain life Internal Structure of the Earth Core innermost layer; solid inner core and liquid outer core; iron- rich. Core innermost layer; solid inner core and liquid outer core; iron- rich. Mantle middle layer; semi-plastic composition. Mantle middle layer; semi-plastic composition. Crust outermost layer; thinnest portion of the Earth. Crust outermost layer; thinnest portion of the Earth. Continental versus Oceanic Crust Oceanic crust made up of dark-colored mineral, basalt; denser than continental crust; younger than continental crust (less than 200 million years old). Oceanic crust made up of dark-colored mineral, basalt; denser than continental crust; younger than continental crust (less than 200 million years old). Continental crust light-colored granite construction mainly; less dense; some crust as old as 3.8 billion years old. Continental crust light-colored granite construction mainly; less dense; some crust as old as 3.8 billion years old. Continental Drift Proposed in 1912 by Alfred Wegner Proposed in 1912 by Alfred Wegner He suggested that all continents had been joined in a single supercontinent which he named Pangaea. He suggested that all continents had been joined in a single supercontinent which he named Pangaea. Fossil remains of extinct reptile Mesosaurus Continental Drift He proposed that Pangaea began breaking up 180 million years ago. He proposed that Pangaea began breaking up 180 million years ago. At the time, his proposal was not widely accepted because he could not explain HOW this occurred. At the time, his proposal was not widely accepted because he could not explain HOW this occurred. What is the name of the process that explains HOW the continents drift? What is the name of the process that explains HOW the continents drift? Theory of Plate Tectonics The Theory of Plate Tectonics Plate Tectonics Plate tectonics explains the HOW behind Wegners continental drift theory Plate tectonics explains the HOW behind Wegners continental drift theory The main features of plate tectonics are: The main features of plate tectonics are: The Earths surface is covered by a series of crustal plates Plate Tectonics The main features of plate tectonics are: The main features of plate tectonics are: The ocean floors are constantly moving; spreading in the center and sinking at the edges and being regenerated. What drives the movement? Convection Currents The force responsible for plate movement is __________. Convection currents Plate Boundaries Divergent Boundary moving _____ Divergent Boundary moving _____ Convergent Boundary moving ________ Convergent Boundary moving ________ Transform Fault Boundary moving ________________________ Transform Fault Boundary moving ________________________ apart together sideways past each other Divergent boundary of two oceanic plates. Creates a __________. Example: ____________ Mid-ocean ridge Mid-Atlantic Ridge Divergent Boundary Convergent boundary of two oceanic plates. Creates an ________ and a _____. Example: _____ island arctrenchJapan Convergent Boundary Convergent boundary of an oceanic plate and a continental plate. Forms a _______ mountain range and a ______. Examples: _______ or _______ Mts volcanic trench Cascades Andes Transform-fault boundary where the North American and Pacific plates are moving ____ each other. Example: ________________ in California past San Andreas Fault Plate Boundaries Review Places where plates move apart are called _____________ boundaries. Places where plates move apart are called _____________ boundaries. When oceanic plates diverge a ___________ is formed. When oceanic plates diverge a ___________ is formed. When two oceanic plates converge what is created? _________________ When two oceanic plates converge what is created? _________________ The force moving the plates is ____________. The force moving the plates is ____________. Convection currents divergent ridge an island arc and a trench Evidence for Plate Tectonics Mid-Oceanic Ridges Mid-Oceanic Ridges The mid-oceanic ridges rise from ocean floor a chain of submarine volcanic mountains Evidence for Plate Tectonics Mid-Oceanic Ridges Mid-Oceanic Ridges at regular intervals, the ridge is displaced by faults in the Earths crust called transform faults San Andreas Convergent Transform Fault Evidence of Plate Tectonics Island Arcs (Aleutian Islands) Island Arcs (Aleutian Islands) Chains of islands are found throughout the oceans, especially in the western Pacific. These "Island arcs" are usually situated along deep sea trenches on the continental side of trenches. Geologic History Pangaea was surrounded by a single world ocean, Panthalassa Pangaea was surrounded by a single world ocean, Panthalassa Geologic History About 150 million years ago, a rift began to form between North America and the combined continents of South America/Africa About 150 million years ago, a rift began to form between North America and the combined continents of South America/Africa This rift separated Pangaea into two large continents, Laurasia and Gondwana This rift separated Pangaea into two large continents, Laurasia and Gondwana This rift was the beginning of the Mid- Atlantic Ridge This rift was the beginning of the Mid- Atlantic Ridge Geologic History Also around 95 million years ago, a rift began to split up Gondwana and the early Indian Ocean began to form Also around 95 million years ago, a rift began to split up Gondwana and the early Indian Ocean began to form Geologic History As the Atlantic Ocean grew (grows), the Americas were (are) carried farther from Eurasia and Africa As the Atlantic Ocean grew (grows), the Americas were (are) carried farther from Eurasia and Africa The Atlantic Ocean to continues to grow and the Pacific Ocean continues to shrink The Atlantic Ocean to continues to grow and the Pacific Ocean continues to shrink Continental Margins The margins of continents are boundaries between continental crust and oceanic crust The margins of continents are boundaries between continental crust and oceanic crust Continental Margins They generally consist of: They generally consist of: Continental shelf (most landward) Continental slope Continental rise (most seaward) The Continental Shelf 8% of the oceans surface area 8% of the oceans surface area Biologically the richest area of the ocean Biologically the richest area of the ocean 1 km (0.6 mi) to 750 km (470 mi) wide 1 km (0.6 mi) to 750 km (470 mi) wide Shelf ends at a depth of 120 200 m (400 to 600ft) Shelf ends at a depth of 120 200 m (400 to 600ft) Continental Slope Can be thought of as the edge of a continent Can be thought of as the edge of a continent Begins at the shelf break and continues to deep sea floor Begins at the shelf break and continues to deep sea floor Much steeper than continental shelf and continental rise Much steeper than continental shelf and continental rise Continental Rise Formed by sediments that have been pushed down from continental shelf and slope Formed by sediments that have been pushed down from continental shelf and slope It can be thought of as an underwater river delta (the river in this case is formed of sediments) It can be thought of as an underwater river delta (the river in this case is formed of sediments) Types of Continental Margins Passive margins: Passive margins: Relatively inactive geologically Characterized by flat, wide coastal plains, wide continental shelves and gradually sloping continental slopes Example: East Coast of US North Carolina barrier island Types of Margins Active Margins: Active Margins: Intense geologic activity: earthquakes, volcanoes and trenches Steep, rocky shorelines, narrow continental shelves and steep continental slopes Example: Monterey Bay, CA