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
-more clouds = warmer surface (Ex: Venus)
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
Earth’s 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
mineral


 Thicker

 Older rock; ~4 bill years ago
 Younger rock; < 200 mil years
Tab. 2.2
The Structure of Earth
Continental and Oceanic Crusts
 Continental crust floats higher on the mantle and
ocean crust floats lower.
 That’s 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
to…Theory 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
 Earth’s 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 earth’s
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