Download Where did the water for the oceans come from?

SUN
Hydrogen (74%),
some helium (24%)
Rocky inner
planets
Silicates with
Iron/Nickel
cores
The giant Gas planets of the outer solar system
Hydrogen, Helium, methane, water,
ammonia
Where did the water for the oceans
come from?
From volcanoes:
• Ammonia (NH3)
• Hydrogen (H2)
• Carbon dioxide (CO2)
• Methane (CH4)
• Water vapor (H2O)
• Nitrogen (N2)
Hadean Oceans
Characteristics
• Liquid Water existed at
4.4 Gyrs
Evidence
• Jack Hills Formation zircon crystals
with water inclusions
•“Ephemeral” (periodically
vaporized)
•solar system evidence for heavy
bombardment and models
• Acidic (water + carbon
dioxide = carbonic acid)
• no limestones, atmospheric
models
•Probably “salty”
•acidic water (dissolves ions)
• Stabilized by end of
Hadean (about 3.8 Gyrs)
• first limestones & sedimentary
rocks
What is different about the Earth?
Tectonically Active: No or very few craters visible. The
lithosphere (rocky outer crust) is moving. (Venus and some
of the moons of Jupiter and Saturn may also be somehat
active) Why is this?
Dynamic Hydrosphere/Atmosphere: Clouds, winds, waves,
currents, etc. (something similar on Jupiter and Mars, but
different in magnitude and/or kind)
Dynamic Biosphere: you can see life on the Earth in the
reflected radiation and in the fact that there is Oxygen in
the atmosphere.
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1 Planet Earth
MAIN IDEA
The major geologic features of Earth's surface are (1) the surface fluids (air and water),
(2) the continents, and (3) the ocean basins. The characteristics of these features
indicate that Earth is undergoing constant change. Earth is unique in the Solar System.
SUPPORTING IDEAS
1.
A comparison of Earth with other terrestrial planets provides an insight into the
distinguishing characteristics of our planet and what makes it unique.
2.
Earth's atmosphere is a thin shell surrounding the planet and is in constant
motion. It is unique in the Solar System in that it is composed of 78% nitrogen and 21%
oxygen.
3.
The hydrosphere is another feature that makes Earth unique. It moves from the
ocean to the atmosphere and over the surface in a great cycle.
4.
The biosphere exists because of water. Although it is relatively small compared
with other major layers of Earth, the biosphere has been a major geologic force
operating at the surface.
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5.
Continents and ocean basins are the principal surface features of Earth.
6.
The continents consist of three major components: (a) shields, (b)
stable platforms, and (c) belts of folded mountains. All these components
show the mobility of the crust.
7.
The ocean floor contains several major structural and topographic
divisions: (a) the oceanic ridge (b) the abyssal floor, (c) seamounts, (d)
trenches, and (e) continental margins.
8.
Earth is a differentiated planet, with its materials segregated and
concentrated into layers according to density. The internal layers based on
composition are (a) crust, (b) mantle, and (c) core. The major internal layers
based on physical properties are (a)lithosphere, (b) asthenosphere, (c)
mesosphere, (d) outer core, and (e) inner core. Material within these units is
in motion, making Earth a changing, dynamic planet.
The Hydrosphere
• Total mass of water on or near the
Earth’s surface
– Covers 71% of Earth’s surface
– ~98% in oceans
– 2% in glaciers, groundwater, lakes and
streams (fresh water)
– The presence of water moderates
climates and shapes the Earth’s surface
Compositional Layers
• Crust
– Continental crust
• Thicker than oceanic crust - up to 75 km
• Less dense - 2.7 g/cm3
• Strongly deformed
• Much older - may be billions of years old
Compositional Layers
• Crust
– Oceanic crust
• Thinner than continental crust - about 8 km
• More dense - 3.0 g/cm3
• Comparatively undeformed
• Much younger - < 200 million years old
• Composed of basalt
Crustal Properties
Crust
Density
continental ~2.8 g/cm3
oceanic
~3.2
g/cm3
Composition Thickness
Felsic
Thick:
20-70 km
Mafic
Thin:
2-10 km
Age
Old:
up to
4 Byrs
Young:
<200 Mys
30_SeaFloor.swf
Ocean Basins
Key Ideas
 Earliest direct evidence for voyaging was from the Mediterranean.
There may well have been intentional or unintentional ocean travel
previous to that time.
 The origins of marine science lie in voyaging – traveling on the
ocean for a purpose, which varied form one culture and time to
another. Technological advances made during voyaging and later
marine exploration led to the rise of scientific oceanography.
 Earth’s shape and circumference were accurately estimated around
230 B.C. at the Library of Alexandria, Egypt. The use of latitude
and longitude for positioning and navigation also began there.
 Polynesian adventurers were the first to perfect methods of
sustained, long-distance, open-ocean travel. Possibly as early as
900 BCE, but surely by 300 AD
 The first systematic voyages of oceanic exploration were
undertaken by the Chinese in the fifteenth century.
Key Ideas Continued…
 Christopher Columbus did not discover North America, and he did not sail around
the world.
 Captain James Cook, Royal Navy, was perhaps the first ocean
observer careful enough to be considered a marine scientist.
 The Challenger expedition was the first purely scientific voyage of
oceanic exploration.
 Polar Studies greatly advanced marine science at the beginning of the twentieth
century.
 Nearly all research is conducted not by individuals but by teams of
specialists working in large, nationally funded oceanographic or
military institutions.
 Satellites are increasingly important tools of oceanographic
research.
A third century B.C. chart showing the system of
latitude and longitude developed by Eratosthenes.
The Chinese Undertook Organized
Voyages of Discovery
Chinese navigators set out in the early 1400s to explore the Indian Ocean,
Indonesia, Africa and the Atlantic. Their ships were laden with gifts designed
to show China’s wealth and degree of civilization! The Chinese invented:
 The central rudder
 Water-tight compartments
 Sails on multiple masts
 marine compass
Benjamin Franklin and the
Gulf Stream
The British Challenger expedition of 1872-1876
was the first oceanic expedition dedicated to
scientific research.
New Ships for New Tasks
Ocean drilling
(sediment and rock),
water sampling
(Temperature, Salinity,
chemistry, etc), Echo
sounders, side scan
radar, submersibles,
Remotely Operated
Vehicles (ROVs) and
now satellites in space
(TOPEX, SeaWifs etc)
Blue = No deposition
What about changes in sea level?
glacial/interglacial timescale
Increase of ~120
meters
What about changes in sea level?
OverFigure
the last5.13
century
Increase of ~15
centimeters
Continental Margins
Components:
1. Continental shelf = the shallow, submerged edge
of the continent
2. Shelf break = the abrupt transition from continental
shelf to the continental slope
3. Continental slope = the transition between the
continental shelf and the deep-ocean floor
4. Continental rise = thick accumulations of sediment
found at the base of the continental slope
Continental
slope
Continental
rise
Deep Ocean Basins
Major features:
• Mid-ocean ridges
• Fracture zones and transform faults
• Hydrothermal vents
• Shallow earthquakes
• Abyssal plains
• Abyssal hills
• Seamounts and guyots
• Oceanic trenches
• Volcanic arcs
• Deep earthquakes
Mid Ocean Ridge Spreading
Abyssal Plains
Abyssal plains = broad flat areas of sediment-covered
ocean floor found between the continental margins and
the mid-ocean ridges
• Typically 4-6 km below sea level
• The flattest surface on Earth
• Sedimentation rates are very slow -- millimeters/1000 years!
• Mostly very fine clay, windblown dust, and shells of
microscopic organisms
• Carbonate sediments are rare, as most of the plain is below
the Carbonate Compensation Depth (CCD)
Continental Margins
Components:
1. Continental shelf = the shallow, submerged edge
of the continent
2. Shelf break = the abrupt transition from continental
shelf to the continental slope
3. Continental slope = the transition between the
continental shelf and the deep-ocean floor
4. Continental rise = thick accumulations of sediment
found at the base of the continental slope
Continental
slope
Continental
rise
Deep Ocean Basins
Major features:
• Mid-ocean ridges
• Fracture zones and transform faults
• Hydrothermal vents
• Shallow earthquakes
• Abyssal plains
• Abyssal hills
• Seamounts and guyots
• Oceanic trenches
• Volcanic arcs
• Deep earthquakes
Abyssal Plains
Abyssal plains = broad flat areas of sediment-covered
ocean floor found between the continental margins and
the mid-ocean ridges
• Typically 4-6 km below sea level
• The flattest surface on Earth
• Sedimentation rates are very slow -- millimeters/1000 years!
• Mostly very fine clay, windblown dust, and shells of
microscopic organisms
• Carbonate sediments are rare, as most of the plain is below
the Carbonate Compensation Depth (CCD)
Oceanic-Oceanic and Oceanic-Continental Subduction Zones
Passive Continental Margin