Transcript The Origin of the Ocean

The Origin of the Ocean
The Water Planet
AN OCEAN WORLD
•
•
•
•
The ocean covers 71% of Earth’s surface
The ocean contains 97% of the water on Earth
The ocean is Earth’s most important feature
The named oceans and seas (Pacific and
Atlantic, Mediterranean and Baltic) are named
for our convenience
• They are only temporary features of a single
world ocean
• Average ocean depth is about 4½ times greater
than the average height of the continents above
sea level
Earth is a Water Planet
• oceans occupy 71% of the earth's surface
• not distributed equally with respect to the
•
•
equator
ocean covers 61% of the northern hemisphere
and 80% of the southern hemisphere
presence of oceans is function of geological
activity and planet's location in relation to sun
– too far away -- water will be in a frozen state
– too close -- water will evaporate
• Earth is in a perfect location to allow water to be
in liquid state
Oceans
• Today's oceans are traditionally divided into 4 large
basins
–
–
–
–
North and South Pacific
North and South Atlantic
Indian
Arctic
• Oceans are really interconnected
• Connected to these 4 large basins are smaller, marginal
seas, such as the Mediterranean, Gulf of Mexico, South
China Sea, Red Sea, Caribbean, Baltic Sea, Bering Sea,
etc.
• Each basin or marginal sea varies in its ability to
support life due to both climatic differences and
shapes and positions of present-day continents
• Ocean basins consist of the deep seafloor (13,00020,000 ft; 4-6 km) and cover most of the earth's surface
(30%); continents only cover 29%
Distribution
of land and
sea by
latitude
Hypsographic Curve
Elevation areas above
And below sea-level
Bathymetric Chart of the Sea Floor
Physiographic Map of the Sea Floor
3-D Computer Generated Image of the East Pacific Rise
The Big Bang
• Event that occurred approximately 13.7
BILLION years ago
• All the mass and energy concentrated at a
point
• The universe began expanding and
continues to expand
• After 1 million years matter began to cool
enough to form atoms- Hydrogen- the
building block of stars
Galaxies and Stars
• Galaxy- huge rotating aggregation of
stars, dust, gas held together by gravity
• Earth, the sun and our solar system is part
of the Milky Way
• Stars are massive spheres of incandescent
gases (hydrogen and helium)
The Solar System
• Our solar system is located away from the
galaxy’s center
• Our sun and the planets originated from a
solar nebula that had been enriched with
heavy elements from nearby super novae
• Solar system is approximately 5 Billion
years old
• Composition is 75% hydrogen, 23%
helium and 2% other materials
Formation of a
Protostar
Center
contracts
Center
continues to
heat up
Protostar
radiates more
heat
Fusion
begins in the
stars core
Shockwaves
radiate
outward
releasing
material
Material
coalesces
into planets,
moons or
comets
Other
material is
ejected to the
periphery
Our Solar
System
4 inner
planets
(terrestrial)
4 outer
planets
(gaseous)
Solar nebula
photographed
by Hubble
The Earth
• Core is composed of mixtures or alloys of iron
•
(pressure is more than a million times that at the
surface and temperature is estimated to be at
4000°C); has a solid inner core and a liquid outer
core (earth's magnetic field may be produced by
the motion of the liquid material in the iron-rich
outer core)
Layer outside the earth's core is the mantle; it is
solid but very hot, near the melting point of
rocks, so it flows almost like a liquid, though
much slower; it is 70% of the earth's volume
The Earth
• Outermost layer is the crust; it is extremely thin
(is thinner under the oceans than under the
continents)
– Oceanic crust is made of basalt (low in silica and
high in iron and magnesium) and has a higher density
compared to continental crust, which is made of
granite (high content of aluminum and magnesium
silicate with quartz and feldspar) and has a lower
density
– Thus, continents lie above sea level and oceanic crust
lies below sea level because of density differences
Formation of the Oceans:
Prevailing Theory
• The major trapped volatile was water (H2O). Others
included nitrogen (N2), the most abundant gas in the
atmosphere, carbon dioxide (CO2), and hydrochloric
acid (HCl), which was the source of the chloride in sea
salt (mostly NaCl).
• The volatiles were probably released early in the Earth's
history, when it melted and segregated into the core,
mantle, and crust. This segregation occurred because
of differences in density, the crust being the "lightest"
material.
• Volcanoes have released additional volatiles throughout
the Earth's history, but probably more during the early
years when the Earth was hotter.
• Probably, the oceans formed as soon as the Earth
cooled enough for water to become liquid, about 4 billion
years ago. The oldest rocks on the earth's surface today
are 3.8 billion years old.
Outgassing
Oceans are byproducts of
heating and differentiation:
as earth warmed and
partially melted, water
locked in the minerals as
hydrogen and oxygen was
released and carried to the
surface by volcanic venting
activity
Creating the Oceans
It is hypothesized that water vapor escaping from
the interior of the Earth via countless volcanic
eruptions created the oceans (this took hundreds
of millions of years)
Creating the Oceans
Astronomers also
hypothesize that
comets impacting the
Earth were a major
source of water that
contributed to creation
of the oceans
Remember, that
comets are best
described as “dirty ice
balls”
Creating the Oceans
The earliest evidence of surface water on
Earth dates back about 3.8 billion years
Geologic Time
Origin of Atmosphere
• Atmosphere evolved in 4 steps:
– primordial gases, later lost from sun's
radiation
– exhalations from the molten surface (volcanic
venting); bombardment from icy comets
– steady additions of carbon dioxide, water
vapor, carbon monoxide, nitrogen, hydrogen,
hydrogen chloride, ammonia, and methane
from volcanic activity
– addition of oxygen by plant/bacterial life
The Hydrologic Cycle
• Water occurs as a solid, liquid and gas
• Amount of water is fixed
• The places where water resides are called
Reservoirs
• Water constantly moves from one
reservoir to another
Comparison of
the amount of
water supply
held in each of
the major
reservoirs
If the total
earth’s water
supply was a 55
gallon drum
The Origin of Sea Salts
• The sea became salty because of chemicals leached
from the rocks of the crust, plus some volatile chemicals
(hydrochloric acid and hydrogen sulfide) released
from the Earth's interior and by volcanoes.
• Probably, the ocean was salty as soon as it formed. More
salts have accumulated gradually, as more of the rocks
of the crust were broken down by water (weathered).
• The composition of the sea salt has been about the
same for about 1 billion years. That is because a balance
exists between input of salts (mainly by rivers) and
output (mainly by sediments).
• The early ocean, 3.8 billion years ago, was probably
similar in composition to today, except for changes
caused by living things. The most important of these is
the production of oxygen by plants.