TOPIC 5 OBJECTIVES EARTH'S HISTORY
1. Given a diagram of sedimentary rocks, sequence the layers according to their relative age using the Law of Superposition.
The Law of Superposition states that with rock layers that are undisturbed the layers on the bottom are the oldest, and the youngest are on the top.
2. Using the Law of Cross-Cutting Relationships, determine the relative age of igneous intrusions, faults, and folds found in rock layers.
The Law of Cross-Cutting states that any rock layer cut by an intrusion or fault is older than the intrusion or fault.
3. Identify four ways by which rocks in one area can be matched, or correlated, with rocks in another area.
A. Walking the outcrop.
B. Index fossils.
C. Key beds.
D. Rock similarities.
4 a. Define fossil.
b. Identify and describe some ways in which fossils are preserved.
A. Actual Remains: Ice and amber
B. Replacement: Petrified wood
C. Molds: Hollow depression left when an organism decays.
D. Casts: When material fills in the mold.
5. Explain the three characteristics of index fossils and/or key beds, which make them useful in interpreting Earth's history.
A. It must be easy to recognize.
B. It must cover a large geographic area.
C. The geologic event or organism must exist for a short period of time.
6. Given a list of geologic eras and periods in the Earth Science Reference Tables (ESRT), match the era and/or period with the predominant life forms that existed at that time.
This information is on page 8 of the ESRT.* Page 8 ESRT *
7. Given the ESRT, analyze the relationship between mountain building events and the inferred positions of Earth's landmasses throughout geologic history.
This information is on page 9 of the ESRT.* Page 9 ESRT *
8. Given a list of geologic events and their approximate ages, construct a time line of geologic history.
Students have to apply information found on page 8 of the ESRT to create a time line.* Page 8 ESRT * This is what they did in lab 5-5.
9 a. Explain the existence of unconformities in rock layers.
An unconformity is when part of the rock record is missing. This happens when rocks are uplifted and exposed to the agents of weathering and erosion. The area then subsides and sediments are deposited on the erosional surface.
b. Using the ESRT, recognize the existence of unconformities in the geologic history of New York State.
The far right hand side of page 8 in the ESRT has a chart that shows the time periods that rocks can be found in New York State.* Page 8 ESRT * There are large gaps in the rock record during the Mesozoic and Cenozoic Eras.
10. Explain the Principle of Uniformitarianism.
Uniformitarianism is the concept that what we observe in nature today, for example gravity, has always worked the same way. If gravity worked some other way in the past then the Law of Superposition would be invalid. If radioactivity worked some other way in the past then absolute dating is impossible.
11. Describe why radioactive substances are useful for determining the age of rocks or other material.
Radioactive materials decay at a constant rate. By knowing this decay rate and the amount of radioactive and decay products in a rock you can determine the age of the rock.
12 a. Define the term half-life.
This is the amount of time it takes for one half of a sample of radioactive material to decay.
b. Given a half-life graph and given the amount of radioactive material unchanged, determine the age of the material.
The students have a worksheet with several examples.
13. Given the ESRT, select the best radioactive element to use to determine the age of a sample depending on the age and composition of the sample.
The chart is on page 16 of the ESRT.* Page 16 ESRT * Carbon-14 is used to date material that was once alive and died fairly recently. Potassium-40, Uranium-238, and Rubidium-87 are used to date rocks. These isotopes have very long half-lives and can be used to date the oldest rocks found on Earth.
14. Describe how the dominant forms of plant and animal life have changed throughout the Eras of geologic history.
Over time the diversity and complexity of life has increased.
15. Using the ESRT, identify the geologic period when life forms have become extinct in the geologic past.
Page 8 of the ESRT has a column describing changes in life through time.* Page 8 ESRT * Changes from one geologic time period, which are also shown on page 8, to another is usually the result of changes in the fossil record, including extinctions. The divides between Eras mark mass extinctions.
16. Given fossils found in New York State, infer the climate, environment, and inferred location of New York State at the time that the fossils were living.
An example would be fossilized coral. This suggests New York State was once the bottom of a shallow, warm sea.
17. Compare human's existence to the overall length of geologic time.
Humans have existed for about .04% of Earth's history.
