Download The Archean Eon

THE FOSSIL RECORD
Movement of Ocean Water
Surface currents
Coriolis Effect
THE FOSSIL RECORD
Movement of Ocean Water
Surface currents
Currents are also affected by the Earth's rotation
through the Coriolis Effect.
Currents in the northern hemisphere tend to be
deflected toward the right (or clockwise), and
currents in the southern hemisphere tend to be
deflected to the left (or counter clockwise) as a result
of the Coriolis Effect.
THE FOSSIL RECORD
Movement of Ocean Water
Thermohaline currents
Thermohaline currents are initiated at the ocean
surface by temperature and salinity conditions.
Gravity acts to pull colder (or more saline) denser
water downward, displacing less dense water
upward.
THE FOSSIL RECORD
Movement of Ocean Water
Thermohaline currents
THE FOSSIL RECORD
Movement of Ocean Water
Tides
Tides are generated by the effect of the Moon's
gravity (and to a lesser extent, the Sun's gravity)
on the oceans.
THE FOSSIL RECORD
Movement of Ocean Water
Tides
Areas that are alternately submerged and exposed
by rising and falling tides are called tidal flats.
THE FOSSIL RECORD
Water Temperature and Depth
Water temperature varies with latitude
THE FOSSIL RECORD
Water Temperature and Depth
Water temperature also varies with depth
THE FOSSIL RECORD
Water Temperature and Depth
A zone of rapid temperature decrease with depth in a
water mass is called the thermocline.
At great ocean depths, temperatures may be just
above freezing.
THE FOSSIL RECORD
Light
The well-illuminated water near the surface of the
ocean is called the photic zone.
THE FOSSIL RECORD
Light
Light is used by certain organisms in the water for
photosynthesis.
Photosynthetic organisms are restricted to the
near-surface waters.
THE FOSSIL RECORD
Light
Light penetration into the sea depends on:
Sun angle
THE FOSSIL RECORD
Light
Light penetration into the sea depends on:
Atmospheric conditions
THE FOSSIL RECORD
Light
Light penetration into the sea depends on:
Conditions at the water surface
THE FOSSIL RECORD
Light
Light penetration into the sea depends on:
Clarity of the water (or conversely, the amount of
suspended sediment in the water)
THE FOSSIL RECORD
Light
In some areas, light may penetrate as deep as 200 m or more,
but generally there is light adequate to support
photosynthesis only in the upper tens of meters of the sea
(to perhaps 100 m).
THE FOSSIL RECORD
Seafloor Sediments
Terrigenous Sediments
Material weathered from the continents
Mostly silt and clay
THE FOSSIL RECORD
Seafloor Sediments
Biogenic or Organic Sediments
Sediment of biologic origin
THE FOSSIL RECORD
Seafloor Sediments
Biogenic or Organic Sediments
Calcareous oozes
Form in depths <4000 m
Foraminifera, coccolithophores,
and pteropods
THE FOSSIL RECORD
Ocean Chemistry
Carbonate Compensation Depth
The Carbonate Compensation
Depth or CCD is a
particular depth in the
oceans (varying from
place to place), which
effects where calcareous
oozes may or may not
accumulate.
THE FOSSIL RECORD
Ocean Chemistry
Carbonate Compensation Depth
Above the CCD, water is warmer,
and precipitation of CaCO3 is
greater than dissolution.
Calcareous plankton can be found
in the water column, and on
the bottom.
Bottom sediments can consist of
calcareous sediments forming
chalk or limestone.
THE FOSSIL RECORD
Ocean Chemistry
Carbonate Compensation Depth
Below the CCD, water is colder, and
CaCO3 tends to dissolve
(dissolution is greater than
precipitation)
Tiny shells of CaCO3 dissolve, and
do not accumulate on the bottom
if water is deeper than the CCD
Below the CCD, the bottom
sediments consist of clay and
siliceous ooze
THE FOSSIL RECORD
Seafloor Sediments
Biogenic or Organic Sediments
Calcareous oozes
THE FOSSIL RECORD
Seafloor Sediments
Biogenic or Organic Sediments
Siliceous oozes
Form in cold, deep water
Radiolarians and diatoms
THE FOSSIL RECORD
Seafloor Sediments
Biogenic or Organic Sediments
Phosphatic sediments
Fish bones and teeth
THE FOSSIL RECORD
Seafloor Sediments
Hydrogenous Sediments
Manganese nodules
(Authigenic or
diagenetic minerals)
Minerals that precipitate
from sea water by chemical
reactions.
THE FOSSIL RECORD
Reconstructing Ancient Geography
THE FOSSIL RECORD
Ancient Climatic Conditions
Fossils can be used to interpret paleoclimates or ancient climates
Fossil spore and pollen grains
THE FOSSIL RECORD
Ancient Climatic Conditions
Presence of corals indicates tropical climates
THE FOSSIL RECORD
Ancient Climatic Conditions
Plant fossils showing
aerial roots,
drip tips on leaves
lack of yearly rings,
large wood cell structure
Indicate tropical climates
THE FOSSIL RECORD
Ancient Climatic Conditions
Marine molluscs (clams, snails, etc.) with spines and thick shells
inhabit warm seas
THE FOSSIL RECORD
Ancient Climatic Conditions
Planktonic organisms vary in size and coiling direction
according to temperature
foraminifer Globorotalia
Right coiled
warm
Left coiled
cold
THE FOSSIL RECORD
Ancient Climatic Conditions
Oxygen isotope ratios in shells.
16O evaporates easier than oxygen-18 because it is lighter.
16O falls as precipitation and gets locked up in glaciers,
leaving sea water enriched in 18O during glaciations.
Shells that are enriched in 18O indicate times of glaciation.
THE FOSSIL RECORD
Ancient Climatic Conditions
THE FOSSIL RECORD
Extinctions
The history of life has been marked by extinctions.
The five largest extinction events are termed mass extinctions.
These mass extinctions were sudden, global in extent, and very
devastating.
Mass extinctions occurred at the ends of the following periods:
Ordovician
Devonian (roughly 70% of the ocean's invertebrates disappeared)
Permian (the greatest extinction. More than 90% of all marine
species at that time disappeared or nearly went extinct)
Triassic
Cretaceous (affecting the dinosaurs ano other animals on land
as well as organisms in the sea, about one fourth of all
known families of animals became extinct)
THE FOSSIL RECORD
Extinctions