A portion of the mid-Atlantic ridge above the sea surface in Iceland. Chapter 2 The Sea Floor What does geology have to do with marine biology? Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Before we start: Marine biology =
Geology = Geo- , Latin for _________ The study of earth's physical structure and substance, its history, and the processes that act on it. Ex: The Water Planet
The Geography of the Ocean Basins The oceans cover _____% of the planet and regulate its ___________ and _____________. There are four ocean basins Pacific Atlantic Indian Arctic
Connected to the main ocean basins are shallow seas Ex: Fig. 2.1 The Geography of the Ocean Basins They all connect to form a world ocean where seawater,
materials, and organisms can move about. Continuous body of water surrounding Antarctica is the Southern Ocean Fig. 2.2 The Structure of Earth Big Bang Theory
http://www.metaphysics-for-life.com/big-bang-theory.html Fig. 2.2 The Structure of Earth In the early molten Earth, naturenplanet.com lighter materials floated toward the surface
because of varying densities. They cooled to form the crust The atmosphere and oceans then formed Earth is the right distance from the sun for liquid water, and life, to exist Water
Exists only on Earth, due to narrow temp. range required for liquid water. Earth is in prime position/size for liquid water Any closer-too hot, water evaporates Any further-too cold, all water freezes Any smaller (~30%) then not enough gravitational pull to keep water on surface, all moves to atmosphere. Any bigger, then too many clouds
-Importance of clouds? Greenhouse Effect How did the water form? As Earth cooled, water vapor in atmosphere condensed, fell to surface, filled up low parts first. Fig. 2.3
The Structure of Earth Internal Structure The dense CORE is mostly ___________. Solid inner core and liquid outer core Believed the swirling motions in outer core produce Earths magnetic field The _____________ is outside the core and under the crust Near molten rock slowly flows like a liquid
The crust is the outer layer, comparatively thin Like a skin floating on the mantle composition differs between oceans and continents The Structure of Earth Continental and Oceanic Crusts Oceanic Crust Continental Crust Made of basalt a dark
M Thicker Older rock; ~4 bill years mineral Younger rock; < 200 mil years ago
Tab. 2.2 The Structure of Earth Continental and Oceanic Crusts Continental crust floats higher on the mantle and ocean crust floats lower. Thats why ocean crust is covered by water Fig. 2.2
The Origin and Structure of the Ocean Basins Earth today: still dynamic Not static and unchanging Continents still moving! Size/Shape of ocean basins defined by continental margins www3.bc.sympatico.ca Continents as
puzzle pieces, S. America and Africa Other evidence: Similar rock formations Fossil records Alfred Wegener 1st to come up with
hypothesis of continental drift 1912. Suggested that all the continents had once been a supercontinent, named ______________. He thought, broke up. -today: ~180 mil years ago tower.com
The Theory of Plate Tectonics More evidence led toTheory of Plate Tectonics. Explains the How Continents do drift slowly around the world Process involves
surface of the entire planet tower.com The Theory of Plate Tectonics Discovery of Mid-Ocean Ridge After WWII sonar allowed detailed maps of the sea floor SONAR = They discovered the mid-ocean ridge system!
Chains of ridges in the middle of the oceans, like seams on a baseball The largest geological feature on Earth tower.com Fig. 2.5 Mid-Ocean Ridge System Some of the mountains rise above sea level to
form islands, e.g. Iceland The Mid-Atlantic ridge runs down the center of the Atlantic Ocean and follows the curve of the opposing coastline Sonar also discovered ____________________= deep depressions in the sea floor. Fig. 2.6 Significance of the Mid-Ocean Ridge Rock near the ridge is young and gets older
moving away from the ridge Significance of the Mid-Ocean Ridge ________________ = loose material like sand and mud that settles on bottom of sea floor. Little sediment near ridge, gets thicker moving away Found symmetric
magnetic bands parallel to the ridge which alternate normal and reversed magnetisms More Evidence: Magnetic Anomalies Earths magnetic field, occasionally reverses direction Magnetic parts in molten rock, free to move. When cool, these particles are frozen and keep their orientation, even if magnetic field
changes. Sea floor rocks have these bands, or magnetic anomalies. Sea floor NOT formed all at once. Creation of Sea Floor Huge pieces of oceanic crust are separating at the mid-ocean ridges Create cracks = rifts Magma from the mantle rises through the rift forming the ridge
The sea floor moves away from the ridge This continuous process is called sea-floor spreading New sea floor is created This explains why rocks are older and sediment is thicker as you move away from the ridge This also explains the magnetic stripes found in the sea floor ALL EVIDENCE for PLATE TECTONICS Fig. 2.9 Cross section of the sea floor at a mid-ocean ridge.
The rocks of the sea floor show the earths magnetism at the time of their cooling. Sea-Floor Spreading and Plate Tectonics The crust and part of the uppermost part of mantle form the ______________________. 100 km (60 mi) thick, rigid
Broken into ______________. May be ocean crust, continent crust, or both The plates float on a fluid layer of the upper mantle called the ________________________. Edge of many plates, a mid-ocean ridge The plates move apart here, to create new sea floor If the plate has continental crust it carries the continent with it. Spread 2-18 cm/year Called continental drift, continents moving apart
Plate Boundaries at Trenches As new lithosphere is created, old lithosphere destroyed somewhere else Some plate boundaries are trenches where one plate sinks below the other, into the mantle and melts This process =__________________ ______________are also called _______________zones The plates colliding can be oceanic cont.
Ocean plates always sink below, denser Produces earthquakes and volcanic mountain ranges; e.x. oceanic cont oceanic oceanic Either plate could have dipped below the other, in this case.
The plates colliding can be oceanic oceanic Earthquakes and volcanic island arcs = volcanic island chain that follow trench curvature Ex: continental continental The plates colliding can be cont. cont. Neither plate sinks, instead they buckle Producing huge mountain ranges
Ex: Fig. 2.14 Shear boundary Another type: shear boundary or transform fault The plates slide past each other Causes earthquakes
Ex: Fig. 2.15 Two forces move the plates: 1) Slab-Pull theory 2) Convection theory Geological History of the Earth 1. Continental Drift and the Changing Oceans 200 mil years ago all the continents were
joined in Pangea It was surrounded by a single ocean called ______________________. 180 mil years ago a rift formed splitting it into two large continents ______________ North America and Eurasia ______________ South America, Africa, Antarctica, India, and Australia Fig. 2.16 The plates are still
moving today. Atlantic __________ Pacific ___________ Geological History of the Earth The Record in the Sediments Studying sediments deposited in past, can learn about the history of the planet Two types of marine sediments: 1) Lithogenous from the weathering of rock on land
2) Biogenous from skeletons and shells of marine organisms Mostly composed of calcium carbonate or silica Microfossils tell what organisms lived in the past Radiolarians: animal-like Protists Foramaniferans:
animal-like Protists Oceans and Climate in the Past Past climate on Earth can be determined by: Chemical composition of microfossils Measure ratios of Mg to Ca
Oxygen isotope ratios Sr and Ca ratios in ancient coral skeletons Ice cores Fossil Agatized Coral is Florida's state stone. 28-25 million years ago Fig. 2.18 Geological History of the Earth
Climate and Changes in Sea Level The Earth alternates between interglacial (warm) period and ice age (cold) periods Sea level falls during ice ages because water is trapped in glaciers on the continents Currently in an interglacial period Pleistocene Epoch , 2 mya, began last ice age Peak was 18,000 yrs. ago The Geological Provinces of the Ocean
2 main regions of the sea floor 1) Continental Margins = -submerged edge of the continents. -boundaries between continental and oceanic crust 2) Deep-sea floor Continental Margins = Boundaries between the continental and oceanic crusts Consists of: Shelf Slope Rise
Continental Margins 1. Continental Shelf The shallowest part Only 8% of the sea floor, but biologically rich and diverse Large submarine canyons can be found here, from past glaciation Ends at the shelf break, where it steeply slopes
down Shelf .6mi to 470 mi wide Continental Margins 2. Continental Slope The edge of the continent Slopes down from the shelf break to the deep-sea floor Submarine canyons can carry sediments from the shelf to the sea floor.
Reaches sea floor at 10,000-16,500 ft underwater A submarine canyon Continental Margins 3. Continental Rise Consists of sediment building up on the sea floor at the base o the slope Some, similar to a river delta = deep-sea fan
Continental Margins 4. Active and Passive Margins Active margin = the subducting plate creates a trench Earthquakes and volcanoes Ex: Narrow shelf steep slope
little or no rise Steep, rocky shorelines Continental Margins 4. Active and Passive Margins Passive margin no plate boundary Wide shelf gradual slope thick rise Ex: see next slide
Passive Margins Example: Atlantic Coast of U.S.A Buildup of sediments Broad coastal plains Estuaries Barrier Islands
Salt Marshes Deep-Ocean Basins Most of sea floor , 10,000-16,500 ft Abyssal plain = the deep sea floor, relatively flat, but has features: Abyssal hills, submarine channels, rises, plateaus Seamounts submarine volcanoes Guyots (gee-oh) flat-topped seamounts Trenches , subduction zones, = the deepest part
of the ocean Mariana Trench is 36,070 ft deep (10,994 m) the deepest on Earth Mid-Ocean Ridge and Hydrothermal Vents At the center of the ridge, where the plates pull apart a depression = central rift valley
Water seeps down through cracks, gets heated by the mantle Then emerges through hydrothermal vents, deep sea hot springs. warm, 68F Some hot, 660F Fig. 2.26 C. Mid-Ocean Ridge and
Hydrothermal Vents Dissolved minerals from the mantle, like sulfides, are brought up Black smokers form when minerals solidify around a vent Marine life, including chemosynthesizers, exist around
hydrothermal vents Fig. 2.27 Chimney-like structures that build up around vents as the minerals solidify. Hawaiian Islands
Part of the Emperor Seamount chain Made from a Hotspot = a place where a plume of magma rises deep in the mantle and erupts. Pacific plate, slowly moving over the stationary hotspot Much debate still, a stationary hotspot or various cracks in the crust. http://www.youtube.com/watch?v=hOCfb9ox_ 90
Page 36 Geology and Marine Biology What does geology have to do with marine biology? Profoundly influences habitats= The natural environment where organisms live Sculpts shorelines Determines water depth
Controls if muddy, sandy, rocky bottom Creates new islands, ridges, mountains for organisms to colonize
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