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Major Concepts in The Geologic History Unit:

How are the Relative Ages of Rocks Determined?

• What is the Law of Superposition?  How does it help geologists begin to interpret the history preserved in the rocks of an outcrop?
• How does the Law of Cross-Cutting Relations help geologists interpret the relative age of intrusions and faults in an outcrop?
• Why is the Law of Original Horizontality so important when interpreting outcrops in seismically active areas?
• What is an unconformity?  How can we fill in the missing time represented by an unconformity in an outcrop?

What evidence has been used to subdivide Geologic Time?

March Through Time! PowerPoint

• On what basis have scientists divided geologic time?  What are the four major "Eras" called?
• What percentage of Earth's history is recorded in the fossil record (starting with the beginning of the Paleozoic Era)?
• How does the analysis of fossils and other evidence in the rock record support the theory of evolution?
• According to scientists, how does the length of human existence compare to all of geologic time?
• EARTH SCIENCE REFERENCE TABLES - Pages 8&9

How Can Rocks that are Separated Geographically be Correlated?

• What are index fossils?  How can they be used to correlate rocks from different areas of the world?
• What are volcanic ash layers?  How can they be used to correlate rocks from different areas of the world?
• What is meant by the term "walking the outcrop"?
• EARTH SCIENCE REFERENCE TABLES - Page 3

How are the Absolute Ages of Rocks Determined?

• How do geologists use the natural radioactive decay of unstable isotopes to determine the ages of rocks?
• What radioactive isotopes are useful for dating recent organic remains?  How about ancient rocks?
• EARTH SCIENCE REFERENCE TABLES - Page 1

Geologic History Practice Questions:

Click here for a practice test with answers!

Geologic History Vocabulary:

Absolute Time
Cenozoic Era
Contact Metamorphism
Correlation
Dike
Epoch
Era
Evolution
Extinction
Geologic Timetable
Half-Life
Hominid
Index Fossil
Isotope
Key Bed
Mesozoic Era
Outcrop
Paleozoic Era
Period
Radioactive Decay
Relative Time
Strata
Superposition
Unconformity
Uniformitarianism

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Copyright 1997-2007, Michael Liener