Relative & Absolute Dating

How to find out how old stuff is.
Relative dating – doesn’t tell you actual age, but you can figure out relative order of
different rock bodies.
Geologic time scale in book (pg. 344), all names on geologic time scale were put in
relative order before we could use more exact methods.
These principles have to do with horizontal rock layers.
1. Principle of Superposition – Things at the bottom are older than things at the top.
2. Principle of Lateral Continuity – Horizontal rock layers will extend in all directions until
they reach the limits of their depositional basin.
3. Principle of Original Horizontality – Sedimentary rock layers/basalt flows, originally
deposited as horizontal layers, so folding or tilting had to come after the rock layer was
deposited.
4. Principle of cross-cutting relationships – For igneous intrusions or faults, the feature
that cross-cuts is younger than the rock that is being cross-cut through.
5. Principle of inclusions – Rock bodies that have pieces of another rock in them
(inclusions). The pieces, or inclusions, come from the older rock unit.
6. Principle of Faunal Succession – Fossils are varied pertaining to different rock layers.
Radiometric Dating: understand concept of Half-life
What are isotopes? Different “flavors” of elements. Different masses, different # of
neutrons. Carbon has 3 isotopes: 12C, 13C, 14C, #’s are atomic mass, which is the # of
protons + # of neutrons. Atomic number: # of protons. Carbon ALWAYS has 6 Protons.
Stable isotopes: useful, but not as useful as using radioactive isotopes to determine
age.
12C, 13C, stable
14C, unstable, radioactive, parent isotope, decays at a constant rate. used to determine
age. Only one type of radioactive isotope, more out there.
14N – daughter isotope, stable.
Age since rock cooled.
14C – 5730 years. For Lots of Geology pertaining to older forms, 14C is not very useful
Overview:
Water:
Oceans and Coasts
-Seafloor and Plate Tectonics
-Ocean Circulation (THC)
-Waves and Tsunamis
-Carbonate Platforms (calcite dissolution and precipitation)
Glaciers:
-Glacial movement
-Glacial Budget
-Glacial Erosion, Transport, and Deposition
-Ice Age Theory
-sedimentary and geomorphological evidence
-evidence from stable isotopes
Tides, gravitational pull from moon, sun also exerts force
thermohaline
Long time scale circulation of ocean (3D)
More saline – more dense (water)
Freshwater freezes easier than saltwater.
Sedimentary and geomorphological evidence
Evidence from stable isotopes
Question: type of question put on knowledge survey on Blackboard. 100-150 questions
that cover all concepts based on lecture.
Calculate your grades on blackboard. Drops lowest two ICA scores and lowest lab
assessment.
Thermohaline circulation – ocean circulation
Driven by temperature and salinity, takes 1000 years for water wo circulate completely
through cycle. North Atlantic (near Greenland sea) warm surface water moving North,
deeper cold water. North Atlantic drift (Gulf Stream) carries warm surface water to
North Atlantic, carries warm air to Europe. Some water starts to freeze, ice made up of
freshwater, seawater is saltier than even before, salinity goes up, denser, starts to sink,
increase in salinity causes ocean water to sink, engine that helps drive this circulation.
Ocean circulation: waves driven mostly by wind, moving in orbital path. See ppt slide,
waves travel through water, circular path. Diameter of circles decreases as you go
deeper and deeper in water. Wave base: lowest point to which the waves move the
water. 2 kinds: Fair weather wave base, storm wave base. Related to wavelength of
waves. 1/2 of the wavelength is the base.
If wavelength is 10 meters, wave base is 5.
Bottom of waves interact with the bottom. Get bigger and bigger, curl over and crash.
Top of wave is then moving faster than bottom. Amplitude increases.
tsunamis or “tidal waves” are caused by movement of the seafloor (earthquake,
volcanoes, etc.). Not really “tidal waves”. Tsunami does not move in orbital path, moves
in straight line about the speed of an airplane. Move very differently than wind-driven
waves.
Wave refraction: bending of waves through different parts of the Earth. Ocean waves
can be refracted also. Headland: piece of land sticking out towards ocean, higher wave
energy. Pocket beach: opposite from headland, where sediment gets deposited.
Overall effect is to “smooth” out the shore
River-dominated delta: (Mississippi) – lobes, branching out.
Wave-dominated delta: (Nile)
Wave refraction & Longshore Drift: Transports sediment along the shore, diagonal
waves. Moves sediment down the shore along shoreline.
Longshore Drift – moves parallel to the shoreline.
Quartz sand – makes up most beaches
Carbonate platform.
Chemically altering silicate rocks removes CO2 from atmosphere.
Carbonate platforms: Carbonate rock, shallow ocean water. Siliciclastic.
Calcium bicarbonate.
Carbonate platforms: Precipitation of calcite, important in carbonate platforms. Different
ways to precipitate:
1. Outgas CO2 (heat water up)
2. Critters
Coral reefs need cold, clear water from open ocean,
Typically don’t see carbonate platforms in places like Alaska.
Movie you can watch online called “Extreme Cave Diving” by Nova. Access through
Albertson’s library, or watch on NOVA.
Glacier deforms internally, flows plastically. Very upper parts of glacier are solid