Origin of ocean basins

The reason for the occurrence of such a huge mass of water on the globe, is still a myth and reality. The reason goes back to the Origin of Earth itself. The exact mode of origin is not precisely known. Scientists assume, both Primary and secondary sources would have given rise to all both air and water on the earth. Two possible sources as internal source (or) external source have been proposed so far. Some of them are attributed towards the theories of origin of the earth.

1. ORIGIN OF OCEAN BASINSORIGIN OF OCEAN BASINS
By
Prof. A. Balasubramanian
Centre for Advanced Studies in Earth
Science,
University of Mysore, India

2. Oceanography is the scientific Oceanography is the scientific
study of seas and oceans. study of seas and oceans.
It is an interesting and
interdisciplinary science.
It includes the subjects like
geography, geology, chemistry,
physics, biology, climatology
and engineering.

3. The Origin of Ocean basins is an important The Origin of Ocean basins is an important
aspect in oceanography.aspect in oceanography.
Oceanography mainly deals with the Oceanography mainly deals with the
following aspects: following aspects:
Geological features of ocean bottom.Geological features of ocean bottom.
Physical conditions with reference to Physical conditions with reference to
ocean water & its temperature.ocean water & its temperature.
Chemical composition of sea water and Chemical composition of sea water and
Marine sediments.Marine sediments.
Biological conditions of marine life Biological conditions of marine life
(Fauna & Flora)(Fauna & Flora)
Role of oceans in controlling global Role of oceans in controlling global
climate, navigation and economy.climate, navigation and economy.

4. Oceanography is sub divided
into
Geological oceanography
Physical oceanography
Chemical oceanography
Biological oceanography

5. Geological Oceanography deals with several
aspects of seas and oceans. The essential
aspects are:
Origin of water and air on earth
Theory of continental drift and crustal
blocks.
Theory of Plate Tectonics and
continuing dynamics of ocean basins.
Spreading of Sea Floor ,
Distribution of Ocean Basins & Coastal
geomorphology.

6. Geological Oceanographic Studies also deal
with
Morphology of ocean bottom and relief
Marine sediments and deposits
Coral Reefs and beach processes
Coastal disasters and management
Air-sea interactions.
Study of marine sediments, submarine
canyons, underwater topography & Corals.

7. At present, Earth has about 1.3
billion cubic Km of water.
This amount is present mostly
in the seas and oceans.
Earth is called as a blue planet,
due to the presence of water.

8. Land
Three important spheres make the planet earth as a unique
member in the solar system. They are the atmosphere,
hydrosphere and the lithosphere. Their combined role lies in
the sphere of all living systems.
Air
Water
Life
Earth

9. First of all, it is necessary to
understand
The origin of land, air and water on
earth.
Origin of water and air on earth is
almost related to each other.
The reason for the occurrence of such a
huge mass of water on the globe, is still
a myth and reality.
The reason goes back to the Origin of
Earth itself.

10. The exact mode of origin is not
precisely known.
Scientists assume, both Primary and
secondary sources would have given
rise to both air and water on the earth.
Two possible sources as internal source
(or) external source have been
proposed so far.
Some of them are attributed towards
the
theories of origin of the earth.

11. Origin of the Earth- theories
Many theories have been prposed.
“Planetesimal Hypothesis” of 1749 proposed
by T.C. Chamberline's on the origin of earth
was probably the First idea about the birth of
earth.
Later, in 1755, Immanuel Kant has proposed
the Ancestral Nebula(mist)- containing cloud
of gas and dust, leading to the generation of
planets from the Sun.

12. Hot Gaseous Nebula
Was thought to be rotating with great rapidity,
initially.
It also underwent cooling and contraction, due
to which the speed increased.
Due to strong centrifugal force along the
equator, materials were thrown away as
successful rings.
These rings cooled down to form solid and
liquidous masses at a later stage.
The same process happened to planets to form
their satellites.

15. Equatorial bulge

16. Release of Proto planets, in sequence
Collapsing proto planets further
released their masses as satellites.

17. Celestial Output: Birth of
Planets
The first set of proto planets were
released with more gas available with
the parental source.
Might have come as a flat-ring to
release all outer planets one by one.
The bigger size to all outer planets
came-in due to this.
Outer planets are lighter planets also.

18. Parental material shortage:
A ring of thin sheet as a second phase was
released by the Sun.
The Inner planets , smaller in diameter were
emerged. These are denser planets with gas
and solid masses.
Planet earth is 4.6 billion years old.
First 1000 million years, there was only the
processes like solidification and
Consolidation of its crust happened.

19. Embryonic Continents:
Initially, embryonic continents were
formed due to cooling.
Partial melting of the mantle produced
the volcanic rocks like Basalts, that
were little in silica.
Origin of a single continental mass was
created.
This was called as Pangaea.

20. The name Pangaea means "All-
earth".
Pangaea was a supercontinent
consisting of all of Earth's land
masses.

22. Outgassing from the earth’s interior
has poured out water masses, through
eruption and other reactions with the
atmospheric gases.
Atmosphere also helped with
sufficient pressure for precipitating the
water on the planet.
Condensation and Precipitation
continued for several thousand years to
form the oceanic water mass.

23. Infant Earth grew in size-
successful in capturing free
atmospheric molecules to form
water masses.
People also attributed to the
Biochemical Synthesis through
mineralization & photosynthesis
for water on earth.

24. Gradual leakage of water
molecules stored in hydrous
minerals of the Earth's rocks was
also considered as a contributing
factor.
Photolysis was also another
mechanism. The radiation can
break down chemical bonds on the
surface of chemical masses.

25. Internal sources:
A sizeable quantity of water would
have been available with in the
material which formed the Earth
initially.
Water molecules would have
escaped Earth's gravity more easily
when it was less massive during its
early stages of formation.

26. Internal Sources provided
CO
2
, water vapor, Nitrogen
and other gases.
Many gases were provided
by volcanic eruptions, hot
springs & Geysers.
All of them are earth-borne
sources.

27. Primitive oceans were first
formed from the water
molecules released from the
interior and atmospheric
precipitation.
These water bodies joined
together to form seas and
interconnected as oceans over a
period of 4.6 billion years.

28. Extraterrestrial sourcesExtraterrestrial sources
People also attributed that the
Earth's water was originated purely
from comets.
This was done as a result of
measurements of the isotope ratios
of hydrogen in the three comets
Halley, Hyakutake and Hale-Bopp.

29. The Shapes of Continents on
opposite sides of the Atlantic
Ocean was noted by several
scholars. Even today we amazingly
see this feature.
It was in 1596, Abraham Ortelius
put forward the Hypothesis of
Continental Drift.
In 1858, Antonio-snider-Pellegrini
illustrated the closed and opened
Atlantic Ocean with a diagram.

32. Theory of Continental Drift
The development of Continental
Drift Hypothesis, has a long
History.
Alfred Wegener, in 1912, developed
the theory of Continental Drift.

34. Alfred Wegener’s Hypothesis:
According to this concept, about 200-300 million
years ago, all continents were attached together
as a single Landmass.
That Single Landmass – Super Continent – was
called as Pangaea.
Thermal expansion and Volcanic activities broke
the Pangaea into new continents.
These new Continents drifted away from each
other due to further expansion of rip-zones.
Wegener was the first to use the terms
“Continental Drift”.

35. Evidence that continents ‘drift’
There are several evidences found to support
this concept.
Similar Fossil patterns across many adjacent
continents
Mesosaurus skeleton – Fresh water reptile -
found in Brazil & South Africa
Land reptile Lystrosaurus fossils from rocks
of same age from locations of South America,
Africa and Antarctica

36. Several living animals being found on
different continents.
Widespread distribution of Permo
carboniferous sediments in South America,
Africa, Madagascar, Arabia, India, Antarctica
and Australia.
Oriented Glacial striations and deposits
called tillites in Gondwana Land.
Similar Coal Deposits in the Eastern United
States and Siberia.

37. Rocks of different ages show a
variable magnetic field
direction.
Magnetic north and south
reverse through time.
Initially it was considered as
Polar Wandering and now it
attributed to Plate movements.

38. Palaeo Magnetism- people
mistook it as Apparent Polar
Wandering.
Study of Palaeomagnetism came
after these studies.
This has provided the geophysical
evidences to support the movement
of lithospheric plates.
The word “Plates” was technically used
from this period.

39. Early in 1953 – Scholars have
introduced the theory of Plate
Tectonics.
Jack Oliver – Geophysicist
provided many seismological
evidences for these findings.
Continental Crust, Oceanic Crust
& Lithospheric plates were
identified as unique features.

40. Asthenosphere:
Scientists believe that below the lithosphere,
there is a relatively narrow, mobile zone in
the mantle called the asthenosphere.
( asthenes in Greek means “weak”)
This zone is composed of hot, semi-solid
material, which can soften and flow after
being subjected to high temperature and
pressure over a geologic time.
The rigid lithosphere is thought to "float" or
move abovet on the slowly flowing
asthenosphere.

41. This diagram illustrates the location of asthenopshere
approximately 100 km below the surface and 60 km
below the continental and oceanic crusts.

42. Lithospheric Plates:
Lithosphere is broken up into 7 to 8
major Tectonic Plates and several minor
plates.
These Plates are Visco-elastic solid rock
bodies.
A tectonic plate (also called
lithospheric plate) is a massive,
irregularly shaped slab of solid rock.

43. Plate size can vary greatly, from a few
hundred to thousands of kilometers
across; the Pacific and Antarctic Plates
are among the largest.
Plate thickness also varies greatly,
ranging from less than 15 km for young
oceanic lithosphere to about 200 km or
more for ancient continental
lithosphere.
Plates ride on the asthenosphere.

44. RADIATION FROM THE EARTH’S INTERIOR
GENERATES CONVECTION CURRENTS

46. Theory of Plate Tectonics
Describes the large scale motions of the
Earth’s lithospheric plates.
Plates move in relation to one another.
Location where two plates meet is called
as Plate boundaries.
These areas are commonly associated with
geological events such as earthquakes and the
creation of topographic features like
mountains, volcanoes and oceanic trenches.

47. Plate boundaries are the home of the
majority of the world's active volcanoes with
the Pacific Plate's Ring of Fire being most
active and famous.
Plate movements happened along three
types of boundaries as:
(a) Convergent (or) Collisional boundaries
(b) Divergent boundaries (Spreading Centres)
(c) Conservative transform boundaries

48. Types of plate boundary
Transform boundaries occur where plates slide, or
perhaps more accurately grind, past each other
along transform-faults. The relative motion of the two
plates is therefore either sinistral or dextral.
Divergent boundaries occur where two plates slide
apart from each other,
Convergent boundaries (or active margins) occur
where two plates slide towards each other commonly
forming either a subduction zone (if one plate moves
underneath the other) or an orogenic belt (if the two
simply collide and compress).

49. Earth’s Crust & Asthenosphere

53. Lateral relative movement of the
Plates varies (0-100 mm per year)
Tectonic Plates – Thick over
Continental crust & Thin over
Oceanic Crust.
Plates move because of the Earth’s
Lithosphere has a higher strength
and lower density than the
underlying asthenosphere.

54. Plate tectonics is a Kinematic
Phenomenon
Dissipation of heat from the
mantle is the source of energy
for plate movements, through
convection (or) large scale
upwelling and doming.

55. The weakness of the
asthenosphere allowed the
Tectonic Plates to move
easily towards a subduction
zone.

56. The three major categories of driving
forces are:
(a)Mantle dynamics related forces
(b)Gravity Forces - Gravitational
Sliding
(c)Earth rotation related forces.
(Subject of study – Tectonophysics)

57. Plate Junctions Lie Beneath the Sea
In 1920, English Geologist Arthur Holmes proposed
that
(i) Plate junctions might lie beneath the sea, and
(ii) Convection currents within the mantle might
be the driving force (1928)

58. Mid Oceanic Ridges
World’s Bathymetric observations
of 1947 have shown the mid
oceanic ridge of the Central
Atlantic.
Floor of the sea bed beneath the
layer of sediments consisted of
basalt and not granite.

59. Oceanic Crust was much
thinner than Continental
Crust
It was identified that the Sea
floor is spreading

60. Mapping of Sea Floors
In 1950, detailed underwater
explorations with geophysical
instruments provided magnetic
striping along the mid oceanic
ridges.
Sea Floor Spreading Hypothesis –
1966.

62. Pangaea started to break up into two Pangaea started to break up into two
smaller supercontinents, called Laurasia smaller supercontinents, called Laurasia
and Gondwanaland, during the late and Gondwanaland, during the late
Triassic. Triassic.
It formed the continents Gondwanaland It formed the continents Gondwanaland
and Laurasia, separated by the Tethys and Laurasia, separated by the Tethys
Sea. Sea.
By the end of the Cretaceous period, the By the end of the Cretaceous period, the
continents were separating into land continents were separating into land
masses that look like our modern-day masses that look like our modern-day
continents. continents.

63. Origin of Oceans:
When the Super Continent Pangaea
broke into
a)Laurasia (encompassing North
America & Eurasia) and
b)Gondwana (containing the remaining
Continents), all the oceans got
originated.

64. The current continental and oceanic
plates include:
the Eurasian plate,
Australian-Indian plate,
Philippine plate,
Pacific plate,
Juan de Fuca plate,
Nazca plate,
Cocos plate,
North American plate,

65. Caribbean plate,
South American plate,
African plate,
Arabian plate,
the Antarctic plate, and
the Scotia plate.
These plates consist of smaller sub-
plates.

66. Distribution of Ocean Basins
Continents Divided the worlds Ocean
Basins.
Continents and ocean basins are the
fundamental relief features of the
globe.
They are considered to be the Relief
features of first order.
Today, about 70.8% of the total surface
of the globe is represented by oceans
and 29.2% is represented by continents.

67. Distribution of oceans in the two
Hemispheres is not uniform

68. Northern Hemisphere:
We have, Overwhelming
dominance of Land areas.
>75% of the total land area is
situated north of the equator.
Hence, it is called Land
Hemisphere.

69. Southern Hemisphere:
Is full of water and hence,
called as Water Hemisphere
It carries 90.6% of the total
oceanic area of the globe

70. Triangular Shapes- an interesting
feature
Continents are arranged in roughly
triangular shapes with their bases along
the north and apices towards the south.
Similarly, oceans are also triangular in
shape with the bases and apices in the
opposite directions (except one or two
seas).

71. Let us see the
Ancient Seas and Oceans
200 million years ago – only
two water masses
a) Panthalassa
b) Tethys Sea

72. The hypothetical proto-ocean
surrounding the landmass - Pangea
was called as Panthalassa.
This is the mother of all oceans.
This was the primordial Pacific
Ocean.

73. Panthalassa
Panthalassa (Greek, meaning 'all sea‘) was
existing during the late Paleozoic and the early
Mesozoic years.
It included the Pacific Ocean to the west and
north and the Tethys Ocean to the southeast.
It became the Pacific Ocean, following the closing
of the Tethys basin and the breakup of Pangaea,
which created the Atlantic, Arctic, and Indian
Ocean basins.

75. Pangaea- to Laurasia & Gondwana land-
during Triassic – Tethys started to shrink

76. Pangaea- Laurasia- Jurassic

77. Pangaea- Laurasia- Cretaceous

78. World Oceans today

79. Gradually, Tethys was closed: stage-1
This diagram illustrates the Mediterranean region 20
million years ago. The Tethys is about to close as Africa
and Eurasia converge.

80. Closure of Tethys- stage 2
By 10 million years ago, plate collisions have sealed off
the eastern Mediterranean, trapping small remnants
of ocean floor in the Black and Caspian Seas.

81. Closure of Tethys- stage 3
By 6 million years ago, Spain and Africa collide, raising
a mountain barrier and sealing off the western end of
the Mediterranean. River inflow is not enough to
maintain the level of the Mediterranean, which dries
out.

82. Plate collisions in Middle east:
Impacts as earth’s natural hazards along these areas.

83. India has fractured the crust of east Asia
into several subplates which have been
pushed far to the east and southeast as
the collision has progressed.

84. This animation illustrates the movement of India towards NE

86. Collision of India & Eurasia

89. Formation of other areas:
By 900 million years ago, a triple junction
formed as the supercontinent Rodinia started
to rift apart.
Between about 800 million and 700 million
years ago, it split in half.
This was one of the most significant rifting
events of all time, because it opened up the
Panthalassic Ocean to the west of Laurentia, a
continent that became North America.

90. Precambrian Plates and Rodinia
The map shown here depicts the period at 750 m.y.
We can see that the continents are assembled into a
supercontinent, only this time North America is in the middle
instead of Africa. This earlier supercontinent has been given the
name Rodinia.

91. The global ocean of Mirovia, an ocean that
surrounded Rodinia, started to shrink
because the Pan-African ocean and
Panthalassa were expanding.
Between 650 million and 550 million years
ago, another supercontinent was forming,
Pannotia, which was shaped like a "V".
Inside the "V" was Panthalassa, outside of the
"V" was the Pan-African Ocean and remnants
of the Mirovia Ocean.

92. Most of Panthalassa's oceanic
basin and crust has been subducted
under the North American plate,
and the Eurasian Plate.
Panthalassa's oceanic plate
remnants may be the Juan de Fuca,
Gorda, Cocos and the Nazca plates,
all four of which were part of the
Farallon Plate.

93. The South China Sea opened as
Borneo moved away from China.
Also, Japan separated from the
mainland, but it is not yet clear
whether this was related to the
collison of India and Eurasia.

94. This animation shows the time
of start at 60 million years ago.
India pushes blocks of Asiatic
crust eastward.
Continental margin rocks
smear along the margin of
Southeast Asia, while the
northern part of India thrusts
beneath Tibet.

95. Gondwana land

99. Assembly of Pangaea:

107. Assembly of Pangaea:
PACIFIC OCEAN & TETHYS SEAS

113. Dynamic Face of the earth:
The map of the Earth is always
changing; not only are the underlying
plates moving, but the plates also
change in size.
The sea level changes over time (as the
temperature on Earth varies and the
poles melt or freeze to varied extents),
covering or exposing different amounts
of crust.

114. Understanding the Origin of
Ocean basins
is a trivial subject of study.
It is very essential due to several
reasons.
It is also believed that life got
originated from the ocean waters.
Oceans play a very significant role
on global climate.