Transcript 2006 Thomson-Brooks Cole Chapter 3 Geology of the Oceans

Chapter 3
Geology of the Oceans
© 2006 Thomson-Brooks Cole
Key Concepts
• The world ocean has four main basins:
the Atlantic, Pacific, Indian, and Arctic.
• Life first evolved in the ocean.
• The earth’s crust is composed of
moving plates.
• New seafloor is produced at ocean
ridges and old seafloor is removed at
ocean trenches.
© 2006 Thomson-Brooks Cole
Key Concepts
• The ocean floor has topographical features
similar to those found on continents.
• The seafloor is composed of sediments
derived from living as well as nonliving
sources.
• Latitude and longitude determinations are
particularly necessary for precisely locating
positions in the open sea, where there are
no features at the surface.
© 2006 Thomson-Brooks Cole
World Ocean
• Primitive earth and formation of the
ocean
– early earth thought to be composed of
silicon compounds, iron, magnesium
oxide, and other elements
– gradually, the earth heated, causing
melting and separation of elements
– water vapor locked within minerals
released to the surface, where it cooled,
condensed, and formed the ocean
© 2006 Thomson-Brooks Cole
World Ocean
• Ocean and the origin of life
– atmosphere formed by gases escaping
from the planet
– no accumulation of oxygen until evolution
of photosynthesis—free oxygen forms
oxides
– Stanley Miller’s apparatus
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
World Ocean
• The ocean today
– 4 major ocean basins: Pacific, Atlantic,
Indian and Arctic
– seas and gulfs
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Continental Drift
• Layers of the earth
– solid inner core—iron- and nickel-rich
– liquid outer core (same composition)
– mantle—thickest layer with greatest mass,
mainly magnesium-iron silicates
– crust—thinnest and coolest, outermost
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Continental Drift
• Moving continents
– Alfred Wegener
– Pangaea, Laurasia and Gondwanaland
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Continental Drift
• Forces that drive continental
movement
– magma convection currents
– midocean ridges form along cracks where
magma breaks through the crust
– at subduction zones, old crust sinks into
the mantle where it is recycled
– seafloor spreading causes continental drift
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Continental Drift
• Evidence for continental drift
– fit of continental boundaries
– earthquakes
– seafloor temperatures highest near ridges
– age of crust, as determined by samples
drilled from the ocean bottom, increases
with distance from a ridge
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Continental Drift
• Theory of plate tectonics
– lithosphere is viewed as a series of rigid
plates separated by earthquake belts
– divergent plate boundaries—midocean
ridges where plates move apart
– convergent plate boundaries—trenches
where plates move toward each other
– faults—regions where plates move past
each other (e.g. transform faults)
– rift zones—where lithosphere splits
© 2006 Thomson-Brooks Cole
Continental Drift
• Rift communities
– depend on specialized environments found
at divergence zones of the ocean floor
– first was discovered by Robert Ballard and
J.F. Grassle in 1977, in the Galápagos Rift
– primary producers are chemosynthetic
bacteria
© 2006 Thomson-Brooks Cole
Ocean Bottom
• Continental margins
– continental shelf, continental slope, and
shelf break
– submarine canyons and turbidity currents
– continental rises
– shaping the continental shelves
• glaciers
• sediments
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Ocean Bottom
• Ocean basin
– abyssal plains and hills
– seamounts
– ridges and rises
– trenches and island arcs
• Life on the ocean floor
– continental shelves are highly productive
– life on the abyssal plains is not abundant
owing to the absence of sunlight
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Composition of the Seafloor
• Sediment—loose particles of inorganic
and organic material
© 2006 Thomson-Brooks Cole
Composition of the Seafloor
• Hydrogenous sediments
– formed from seawater through a variety of
chemical processes
– e.g. carbonates, phosphorites
• Biogenous sediments
– formed from living organisms
– mostly particles of corals, mollusc shells,
shells of planktonic organisms
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Composition of the Seafloor
• Terrigenous sediments
– produced from continental rocks by the
actions of wind, water, freezing, thawing
– e.g. mud (clay + silt)
• Cosmogenous sediments
– formed from iron-rich particles from outer
space which land in the ocean and sink to
the bottom
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Finding Your Way around the
Sea
• Maps and charts
– Mercator projections
– bathymetric charts
– physiographic charts
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Finding Your Way around the
Sea
• Reference lines
– latitude
– longitude
– divisions of latitude and longitude
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Finding Your Way around the
Sea
• Navigating the ocean
– principles of navigation
• a sextant was used to determine latitude
based on the angle of the North Star with
reference to the horizon
• longitude determined using chronometer
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole
Finding Your Way around the
Sea
• Navigating the ocean
– global positioning system (GPS)
• utilizes a system of satellites to determine
position
• GPS measures the time needed to receive a
signal from 3 satellites, and calculates position
© 2006 Thomson-Brooks Cole
© 2006 Thomson-Brooks Cole