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Chapter 2 Lecture Slides Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Do Now • What was the period in history known as when scientific inquiry came to a stand still? • Who was the first sea captain to have a naturalist among his crew? • Why was the challenger expedition so important to the field of marine science? Objective • Finish up history- (Friday) • SWBAT: Describe major topographic features present on the sea floor. Chapter Two The Sea Floor Modern Marine Biology • Today, several marine biology research stations • exist in locations around the world. In the United States, several facilities are considered to be among the best in the world, including: – Woods Hole Marine Biological Lab, MA – Scripps Institute - La Jolla, CA – Friday Harbor Labs, WA Important Tools of the Trade • Remote sensing – satellites are used to view large • • • expanses of ocean at the ocean’s surface only. Sonar – used to map seafloor depths and formations. Scuba – used for direct human exploration of oceanic environment for longer periods and at deeper depths than would otherwise be available to man. Remotely operated vehicles (ROV’s) – allows for direct exploration of marine environment when scuba is not an option; these ROV’s can be manned (such as Alvin mentioned in chapter 1 readings) or unmanned. Important Tools of the Trade • Research vessels – these floating laboratories allow oceanographers and marine biologists to explore the marine environments for weeks, months or even years without returning to a land-based facility. • Underwater Research Station - Aquarius – underwater research and residential facility located in the Florida Keys. This underwater lab is located approx. 60 feet underwater and allows researchers to stay at this depth for days or weeks without surfacing (eating, sleeping, laboratory work, etc. – everything is done here (think of it like an airtight Winnebago!) Read more about Aquarius at http://www.uncw.edu/aquarius/ Geography of the Ocean Basins • 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. • The world ocean is divided into four large basins: Pacific, Atlantic, Indian and Arctic. Ocean Basins • Which is the largest? • Which is the shallowest? • Which two are similar in size? • Which is the deepest? Structure of the Earth • 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 • This allowed materials to settle by density as the materials cooled Structure of the Earth • Heavier materials settled deep in the Earth • Lighter components formed a thin crust • Eventually, the Earth’s oceans and atmosphere began to form • Earth’s 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. • Mantle – middle layer; semi-plastic composition. • 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). • Continental crust – light-colored granite construction mainly; less dense; some crust as old as 3.8 billion years old. Check for understanding • Which type of crust is the thinnest? • Which type of crust is the oldest? • What 2 layers of the earth make up the lithosphere? Continental Drift • Proposed in 1912 by Alfred Wegner • He suggested that all continents had been joined in a single supercontinent which he named Pangaea. • He proposed that Pangaea began breaking up 180 million years ago. • At the time, his proposal was not widely accepted by he could not explain HOW this occurred. Pieces of evidence to support Continental drift theory 1) Landforms- The shore line of South America would fit with the Africa shore. Mnts. In South Africa line up wit Mnts is Argentina. Coal fields in Brazil match with coal fields in Africa. 2) Fern-like fossils have been found in Africa, South America, Australia, India, Antarctica 3) Continents were exposed to different climates. (Example: deep scratches in rock showed that glaciers once covered South Africa. South Africa was closer to the South Pole. Plate Tectonics • Plate tectonics explains the “HOW” behind Wegner’s continental drift theory • The main features of plate tectonics are: – The Earth’s surface is covered by a series of crustal plates – The ocean floors are constantly moving; spreading in the center and sinking at the edges and being regenerated. – Convection currents beneath the plates assist movement – Heat from the mantle drives these currents Topography on sea floor… • http://www.youtube.com/watch?v=GyMLl Lxbfa4 • Who was Harry Hess? • What is the 12,000 mile Mnt range at the bottom of the • • • ocean called? How high is a Mnt at the bottom of the ocean? What did Hess discover and what did he call his discovery? Why doesn’t the earth grow in size? Evidence for Plate Tectonics • Mid-Oceanic Ridges – The mid-oceanic ridges rise from ocean floor – a chain of submarine volcanic mountains – at regular intervals, the ridge is displaced by faults in the Earth’s crust called transform faults – Very little sediment is located at the bottom near these ridges; sediment gets thicker away from the ridges signifying that the crust further from the ridge is older Mid ocean ridge system • Continuous chain of submarine volcanic Mnts • Like the seam on a base ball (encircle the globe) • Largest feature on the surface of our earth Trenches • Deep depressions in the sea floor • Common in the Pacific Diagram • Draw a picture and write a description • Draw the sea floor include a ridge system and a trench. • Label where sea floor spreading occurs and where subduction occurs. • Describe why the earth does not grow in size if sea floor spreading occurs. Critical thinking… • Where would you find the oldest rocks on the sea floor? • Where would you find the youngest rocks on the sea floor? Vocab • Pangea • Basalt • Lithosphere • Mid-ocean ridge • Trenches Cool animation! • http://www.youtube.com/watch?v=ryrXAG Y1dmE • Convection currents Exit Ticket • T or F? The ocean is equally distributed around our globe • What is oceanic crust made of? • Name 2 pieces of evidence that support continental drift theory Do Now • What are the four major ocean basins? • Compare oceanic crust to continental crust Oceanic Continental • What theory described the “HOW” of Wegner’s continental drift? • What geogrpahic feature is commonly seen near ocean trenches? Objective • SWBAT: Describe why banding patterns are present on the ocean floor • Describe the difference between lithogenous and biogenous sediment • Identify the 4 margins of the continent Earth’s Magnetic Field The earth has an electric field A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. Think of it like a giant bar magnet inside the earth Evidence for Plate Tectonics • Geomagnetic Anomalies: – Occasionally, at random intervals, the Earth's magnetic field reverses. New rock formed from magma records the orientation of Earth's magnetic field at the time the magma cools. – Studies of the sea floor revealed "stripes" of alternating magnetization parallel to the mid-oceanic ridges. This is evidence for continuous formation of new rock at these ridges. As new rock forms, older rock is pushed farther away from the ridge, producing these patterns in the rock. Wait….what? • Sometimes the magnetic field is like this North North Pole • Pole Magnetic North Magnetic South South Pole Magnetic South South Pole Magnetic North • Sometimes the magnetic field looks like this Magnetic Pole Reversals and Sea Floor Spreading • http://www.youtube.com/watch?v=BCzCm ldiaWQ • Draw a diagram of a mid ocean ridge site • Include the banding pattern seen on the ocean floor • Write a caption of why this striped pattern occurs Evidence of Plate Tectonics • Island Arcs – 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. – These observations, along with many other studies of our planet, support the theory that underneath the Earth's crust is a layer of heated rock driving the creation of new ocean floor. Island arcs • Define “seamount” • How long ago did the youngest of the Hawaiian islands form? • How old is the oldest Hawiian island • What does the direction of the island reveal? • How could so many different kinds of fruit flies have evolved in such a short amount of time? Marine Sediments • Lithogenous sediments – derived from the break-down of rocks (weathering) • Biogenous sediments – derived from the skeletons and shells of marine organisms Diatoms Radiolarians Foraminiferans Coccolithophorids What Can We Learn from Sediments? • Biogenous sediments (composed of microfossils) can reveal information from the past • Age of these sediments can be determined using carbon dating • Ocean temperature at the time the microfossils were formed can be determined by looking at the ratios of magnesium to calcium or by different ratios of oxygen isotopes Continental Margins • Continental Shelf • Continental Slope • Continental Rise • Abyssal Plain • Draw a diagram and label each margin – take notes on your diagram about its characteristics • Page 33 Continental Margins • The margins of continents are boundaries between continental crust and oceanic crust • They generally consist of: – Continental shelf (most landward) – Continental slope – Continental rise (most seaward) The Continental Shelf • Makes up about 8% of the ocean’s surface area • However, it is biologically the richest area of the ocean • The width varies from 1 km (0.6 mi) to 750 km (470 mi) • Shelf ends at shelf break which occurs at a depth of 120 – 400 m (9400-1300 ft) Continental Slope • Can be thought of as the “edge” of a continent • Begins at the shelf break and continues to deep sea floor • Much steeper than continental shelf and continental rise Continental Rise • 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) Vocab • • • • • • • • Geomagnetic anomolies Seamounts Island arcs Lithogenous Biogenous Diatoms Radiolarians Foraminifera • • • • • • Coccolithophorids Continental shelf Continental slope Continental rise Abyssal plain Deep sea fan Exit Ticket • Why do we see a banding pattern in the sea floor? • What is a seamount? • What is the difference between lithogenous and biogenous sediment? • What comes after the continental shelf? Do Now • What is the difference between Lithogenous and Biogenous sediments? • Name 2 types of Biogenous sediments (name one that’s made out of CaCO3 and one made out of silica) • What do the banding patterns on the sea floor tell us about how the sea floor formed Objective • SWBAT: Describe the differences between active and passive margins • Describe how and why black smokers form around ocean ridges Run down for today…. • Sediment types • Continental margin profile graphing sheet • Active vs. Passive Margins • Black smokers (possibly) • SEA FLOOR QUIZ Passive and Active Margins Active vs. Passive Margins pg35 • Active • Passive Types of 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 Types of Margins • Active Margins: – Sites of more intense geologic activity including earthquakes, volcanoes and trenches – Characterized by steep, rocky shorelines, narrow continental shelves and steep continental slopes – Example: West Coast of US Deep Ocean Basins • The abyssal plain – Rises at a gentle slope towards the mid ocean ridge system. • Flat with some channels, low abyssal hills, plateaus and rises • Seamounts • Mariana Trench- 36,163 ft deep Hydrothermal Vents • Central rift valley • Black smokers • Life discovered around the hydrothermal vents • http://www.youtube.com/watch?v=rFHtV RKoaUM Quiz time • Sea Floor Quiz • Then article and summary • You will turn in the graph today Exit Ticket • What is the central rift valley? • What type of margin is characterized by a steep slope? • What is the most abundant type of sediment on the open ocean floor?