Marine Biology - Chapter 2 - The Sea Floor

1. THE SEA FLOOR

3.  about 4.6 billion years old
 Geology: the science that deals with the
dynamics and physical history of the earth,
the rocks of which it is composed, and the
physical, chemical, and biological changes
that the earth has undergone or is
undergoing

4.  In most cases we will discuss geology in
terms of habitats, the places in which
organisms live

5.  Oceans cover 72% of the globe and 80% of
that is still considered undiscovered
◦ 2/3 of the earth’s land mass is in the Northern
Hemisphere, which is only 61% ocean
◦ 80% of the Southern Hemisphere is ocean

7.  1. Pacific - Largest and
deepest
◦ almost as large as the
other 3 combined
 2. Atlantic - Second
largest
◦ similar to Indian in avg.
depth
 3. Indian - Third largest
◦ similar to Atlantic in avg.
depth
 4. Arctic - Smallest and
shallowest

8.  All four basins are connected
 This connection is most obvious when the
world is viewed form the south pole
◦ Fig 2.2

9.  Oceanographers often speak of one world
ocean
 World Ocean: Refers to the continuous body
of water that surrounds Antarctica as the
Southern Ocean

11.  The Earth and our solar system is thought to
have originated about 4.6 billion years ago
from clouds or clouds of dust.

 Big Bang: A great cosmic explosion that is
estimated to have occurred 13.7 billion years
ago in which dust particles collided with each
other merging into larger particles that again
collided with each other eventually building
up the earth and other planets

12.  Density: the mass of
a given volume of a
substance;
Mass/Volume
 When the Earth was
formed it was most
likely molten
◦ This allowed the
interior of the Earth to
form based on density
 Fig 2.3

14.  Core: Innermost layer of the Earth that is
composed mainly of iron
◦ Pressure at the core is more than a million times
the pressure on the Earth’s surface
◦ Made up of a solid inner core and a liquid outer
core
◦ It is thought that the swirling motions of the liquid
material in the iron-rich outer core produce the
earth’s magnetic field

15.  Mantle: The layer
outside the earth’s
core
◦ most of it is thought
to be solid, but very
hot - near the point
of melting rock
◦ much of the mantle
slowly flows almost
like liquid

16.  Lithosphere: The fairly rigid layer of the
earth’s surface composed of the crust and
upper-most part of the mantle.
◦ About 100 km (60 mi) thick
◦ Means “rock sphere”
◦ Broken up into a number of plates called
lithospheric plates
 Lithospheric Plates: A part of the lithosphere
that can contain continental crust, oceanic
crust, or both

18.  Asthenosphere: The denser, more plastic
layer of the upper mantle on which the
lithosphere floats
 The distinction between the lithosphere and
the asthenosphere is based on how easily the
rock flows

19.  Crust: The outermost layer of the earth
◦ extremely thin in comparison to the other layers of
the earth
◦ Earth’s skin

21.  The geological
distinction
between ocean
and continents
results from
physical and
chemical
differences in
the rock that
makes up the
crust

22.  Oceanic crust: The
earth’s crust that
makes up the sea
floor, generally
made up of the
mineral basalt
◦ Denser than
continental crust
◦ Thinner than
continental crust

23.  Continental crust: The earth’s crust that
makes up the land portions of the world,
most continental rocks are made of granite
◦ Older than the oceanic crust

24. There is constant geological
change

25.  Sir Francis Bacon
◦ noted that the coasts of the continents on opposite
sides of the Atlantic fit together like pieces of a
giant puzzle
◦ Evidence in coal deposits, geological formations,
and fossil findings

26.  Alfred Wegener
◦ German geophysicist
◦ proposed the first
detailed hypothesis of
continental drift in 1912
◦ suggested that all the
continents had once been
a single “supercontinent”
he named Pangaea
 biggest obstacle was his
inability to explain how
this had occurred

27.  Continental drift: The movement of
continental masses on the surface of the
earth

28.  Pangaea: The single large landmass, or
supercontinent, that broke up to form today’s
continents (Fig 2.16a)
 One giant sea called Panthalassa which is the
ancestor of the modern Pacific

29.  Theory of plate tectonics: The process
involved in the movement of large plates on
the earth’s crust

31.  Mid-ocean Ridge: A continuous chain of
submarine volcanic mountains that encircles
the globe like the seams on a baseball
◦ The largest geological feature on earth
◦ Displaced at locations by cracks known as faults
◦ Occasionally these mountains rise so high that they
break the surface to form islands such as Iceland
and the Azores
◦ Earthquakes tend to cluster near the sites of ridges

32.  Fault: A crack in the earth’s crust usually
formed when two pieces of crust are moving
past each other

33.  Mid-Atlantic Ridge: a chain of submarine
volcanic mountains that runs down the center
of the Atlantic Ocean, closely following the
curves of the opposing coastlines.
◦ The ridge forms an inverted Y in the Indian Ocean
and runs up the eastern side of the Pacific
◦ The main section of ridge in the Eastern Pacific is
called the East Pacific Rise.

35.  Surveys of the sea floor also revealed a
system of trenches
 Trench: A deep depression in the sea floor
◦ especially common in the Pacific
◦ Usually many volcanoes nearby
◦ Lithosphere is destroyed

36.  A trench is formed when two plates collide and
one of the plates sips below the other and
sinks back down into the mantle
 Subduction: The downward movement of the
plate into the mantle
 Trenches are also known as Subduction Zones

38.  The nature of the sea floor is related to the
mid-ocean ridge
 Sea floor rock right near the ridge is very
young and the rock gets progressively older
moving away from the ridge

39.  Sediment: Loose
material like
sand and mud
that settles to
the bottom,
layers get thicker
at greater
distance from
the ridge

40.  From time to time the earth’s magnetic field
reverses direction
◦ Reversals happen every 700,000 years on average
◦ thought to be related to movements of material in
the earth’s outer core
 Many rocks contain tiny magnetic particles
 Magnetic Anomalies: Magnetic bands or
“stripes” in the sea floor running parallel to
the mid-ocean ridge

42.  Rifts: Cracks in the oceanic crust separating
at the mid-ocean ridges
 releases some of the pressure form the
underlying mantle
 allows hot mantle material to melt and rise up
through the rift
 magma pushes up the oceanic crust around
the rift to form the mid-ocean ridge (Fig. 2.9)

43.  Sea-floor Spreading: The entire process by
which the sea floor moves away from the
mid-ocean ridges to create new sea floor
 Also known as spreading centers
 explains crust and sediment build up, and
magnetic anomalies

46.  Continental margins: are the boundaries
between continental crust and oceanic crust
 The shallowest part of the continental
margin is the continental shelf
 consists of the shelf to shelf break,
continental slope, continental rise to
abyssal plains

47.  Continental shelf
 make up about 8% of the ocean’s surface
area
 biologically richest part of the ocean
◦ most life and best fishing
◦ composed of continental crust
 The continental shelf ends at the shelf
break where the slope abruptly gets steeper

49.  Two types of margins
 Active Margins: zones of intense geological activity,
including earthquakes and volcanoes
◦ ex. South America’s western coast
 Passive Margins: zones of little geological activity
with flat coastal plains, wide shelves and gradual
continental slopes
◦ ex. South America’s eastern coast

52.  Ocean sediment holds many clues to the
earth’s past
 Most marine sediments are of two basic
types:
 lithogenous sediment: which is derived from
weathering and is usually deposited near
coasts
 biogenous sediment: which consists of the
shells and skeletons of marine animals

53.  some biogenous sediment is composed of
calcium carbonate (CaCO3)
 This is called calcareous ooze

54.  Uses the isotope C14 to age a fossil
 Half-life of 5,700 C14 to tell the age of the
fossil, the percentage of C12 remains
constant
 Can date something up to 50,000 - 60,000
years old

56.  Global warming is the increase in the average
temperature of the Earth’s near surface air
and oceans since the mid-20th century, and
its projected continuation

57.  Increasing global temperature is expected to
cause sea levels to rise, an increase in the
intensity of extreme weather events, and
significant changes to the amount and
pattern of precipitation

58.  Likely leading to an
increase in tropical
areas and increased
rates of desertification,
changes in agricultural
yields, modification of
trade routes, glacier
retreats, mass species
extinctions and
increases in the ranges
of disease vectors