Chapter 21.1 & 21.2 Notes packet
Chapter 21.1 Notes- The Geologic Time
1. What lead to the development of the geologic time scale?
-The fact that the Earth is constantly changing.
2. What is a geologic Column?
-An ordered arrangement of rock layers based on the ages of the rocks
3. Draw a Geologic Column.
-Rock Layers are distinguished by the types of rock and index fossils that are
found in the rock layers.
-Scientists can date rocks without any radioactive dating.
4. How is geologic time divided up?
-Uses major changes such as alterations in the Earth’s surface or climate
AND the Extinction of organisms.
5. What is an era?
- The largest unit of geologic time.
6. What are the 4 eras?
-Precambrian Era
-Paleozoic Era
-Mesozoic Era
-Cenozoic Era
6. What’s Special about the Precambrian?
-Covers the longest time period (90%)
7. What organisms were abundant during that time?
- Primitive worms, Sponges and Soft corals. Everything was soft, which is
why finding fossils for this time is difficult.
8. What does Paleozoic mean?
-Ancient Life
9.What organisms were abundant during that time?
-Large variety of Marine life, Plant life, and animals.
10. What does Mesozoic mean?
-Middle Life
11. What organisms were abundant during that time?
-Marine Life, Reptiles, Birds, and Primitive Mammals
12. What does Cenozoic Mean?
- Recent Life
13. What is special about the Cenozoic?
-The Current Era
14. What organisms are abundant during this time?
- Marine and Land plants and Animals – Mammals Dominate
15. What mnemonic is used to remember the order of the eras?
-Purple People Make Cheese
16 What are eras divided into?
-Periods
17. What is used to identify each period?
- Specific Fossils
18. What are periods divided into?
-Epochs
19. When do Epochs occur, and Why?
- During the Cenozoic Era
- The abundant Fossil Record.
21.2 Notes- Determining Relative Age.
1. What is Relative Age?
-Not the Exact age of the rock layers, but is determined by the order the
layers are layed down. Usually oldest on the bottom and youngest on the top.
2. What is Strata?
The Rock Layers
3. How old is the earth?
- 4.6 Billion Years old
4. What does the Principle of Uniformitarianism state?
- Current geologic processes that shape the earth today, are the same
geologic processes that shaped the Earth in the past.
-Examples – Volcanoes, Earthquakes, weathering & Erosion.
5. What is Law of Superposition?
-states that an undeformed sedimentary rock layer is older than the layers
above it and younger than the layers below it.
6. What is a bed?
- Sediments that accumulates, compresses, and hardens into rock layers.
7. What is a bedding plane?
- Boundary between 2 rock beds.
8. Draw something that is stratified.
9. What is an Unconformity?
- Indicates a period of time when deposition stopped, where rock was
removed by erosion, and deposition resumed.
10. What is an unconformity caused by?
- Movement of the earth’s crust
11. What are the 3 unconformities?
- Nonconformity
- Angular Unconformity
- Disconformity
12. What is a Nonconformity caused by?
- Unstratified rock (unlayered) lifted up, eroded, and sediment accumulates
on eroded surfaces
13. What does a Nonconformity look like?
- Stratified Rock (layered) lays upon unstratified rock.
-Draw it.
14. What is an Angular Unconformity caused by?
-horizontal layers are tilted or folded then eroded and new layers are
deposited on top of the tilted layers.
15. What does a Angular Unconformity Look like?
- horizontal layers over angled layers.
-Draw it.
or another example:
\
#4 is finished angular unconformity (bent)
16. What is a Disconformity caused by?
- Ocean floor lifted above sea level without being folded or tilted, is eroded
away and eventually falls below sea level again and deposition resumes.
17. What does a Disconformity look llike?
- Horizontal layers over horizontal layer that have been eroded.
- Draw it.
18. What does the Law of Crosscutting Relationships say?
- A fault or an intrusion is always younger than the rock layers that it cuts
through.
19. What is the Law of Crosscutting Relationships caused by?
- Tectonic forces (Movement of the earth’s plates)
20. What is a Fault?
- A break or a crack in the earth’s crust.
21. What is an Intrusion?
- A mass of igneous rock formed when magma is injected into rock layers
and cools and crystallizes.