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EARTH'S HISTORY 2
LESSON 6: DATING
HOW TO DATE A DEAD THING
RELATIVE ROCK LAYER RULES
FOR YOUR NOTEBOOK:
DATING
Lesson 6:
Relative Age Dating- studying the order in which geologic events occurred
Strata- layers of rock
Stratigraphy- the study of layers of rock to determine relative ages
Rules of Relative Age Dating:
Original Horizontality- sedimentary rocks are deposited in horizontal layers
Superposition- the oldest rocks are at the bottom and each layer after that is younger than the layer beneath it
Intrusions/Faults- also known as cross-cutting relationships, an intrusion or fault is younger than the rock it cuts across
Rock/Fossil Correlation- fossils found in older layers contain older organisms
More:
Inclusions- the fragments in a rock layer must be older than the rock layer that contains them
Unconformities- when an eroded area is covered at a later time by a new layer of sediment and creates a gap in the rock record
Key bed- distinctive rock layers deposited over wide geographic areas can be used as markers to determine superposition
Absolute Age Dating- determining the numerical age of rocks and fossils by measuring the decay of radioactive isotopes
Radiometric Dating- using radioactive isotopes to date objects
Radioactive Decay- radioactive isotopes decay over time and give off particles that result in a change to another isotope
Half-life- the length of time it takes for one half of the original isotope to decay
Radiocarbon Dating- C-14 is used to determine the age of organic materials that contain lots of carbon
TREE RINGS
Tree rings: Image of tree rings showing wide rings (fast growth in good conditions) narrow rings (little growth in drought conditions) Tree ring chronologies can span up to 10,000 years!
ICE CORES
Ice cores: Summer ice has more bubbles and larger crystals; used to study climate change. Thousands of meters of ice cores are stored at a facility in Colorado and other facilities around the world.
VARVES
Varves: bands of alternating light and dark-colored sediments of sand, clay, and silt; summer deposits are usually lighter and thicker and contain sand-sized particles with organic matter while winter deposits are made up of darker and thinner fine-grained sediments. These depositions can date glacial sedimentation up to 120,000 years!