Study Guide for the Earth History Post Test
Test Date: Friday, 4 Dec
Ch 8 section 1 p. 318
1. In general, how does a fossil form?
Most fossils are formed when living things die and are buried by sediments. The sediments slowly harden into rock and preserve the
shapes of the organisms.
2. Which parts of an organism are most likely to be preserved as fossils? Why?
Hard parts of an organism usually form fossils because they are less likely to be lost by decay.
3. What are two things that scientists can learn from the fossil record?
Past environments and how groups of organisms have changed over time
4. What does the fossil record show about how life has changed over time?
Life on Earth has evolved, or changed over time. Simple organisms have given rise to more complex plants and animals.
Ch 8 section 2 p. 325
1. In your own words, define the terms relative age and absolute age.
Relative age states whether a rock is younger or older than another rock. Absolute age is a rock’s age in years.
2. A geologist finds a cliff where the edges of several different rock layers can be seen. Which layer is the oldest? Explain using the
correct law.
The bottom; it was the first to be formed by deposits. In horizontal layers of sedimentary rock, the oldest layer is at the bottom, and
each higher layer is younger than the layer below it.
3. Besides the law of superposition, what are three types of clues to the relative age of rock layers?
Igneous rock intrusions and extrusions, faults, and unconformities
4. Compare and contrast extrusions and intrusions.
Both form from molten material. Lava that hardens on the surface is an extrusion. Magma that cools below the surface is an
intrusion.
5. An intrusion crosses an extrusion. Which layer is the older? Explain.
The extrusion; intrusions are always younger than the rock layers through which they pass.
6. The fossil record shows that horseshoe crabs have existed with very little change for about 200 million years. Would horseshoe
crabs be useful as an index fossil? Explain why or why not.
No. They have existed with little change for a long time.
Ch 8 section 3 p. 331
1. How does the composition of a rock containing a radioactive element change over time?
The amount of the radioactive element decreases. The amount of the new element increases.
2. What method do geologists use to determine the absolute age of a rock?
Radioactive dating
3. Why is it difficult to determine the absolute age of a sedimentary rock?
The particles in sedimentary rocks are made up of different substances of different ages.
4. A geologist finds a fossil in a layer of sedimentary rock that lies in between two igneous extrusions. How could the geologist
determine the age of the fossil?
The scientist could use radioactive dating to find the ages of the two igneous extrusions. The age of the sedimentary rock would be
somewhere in between the two ages.
Ch 8 section 4 p. 335
1. What information did geologists use in developing the geologic time scale?
Scientists studied rock layers and fossils worldwide and placed Earth’s rock layers in order by relative age. Later, radioactive dating
helped them determine the absolute ages of the divisions.
2. What are the basic units into which the geologic time scale is divided?
Eras and periods
3. Study Figure 14. Which major division of geologic time was the longest?
Precambrian Time
4. Place the following in the correct order from earliest to latest: Tertiary, Jurassic, Quaternary, Triassic, Cretaceous.
Triassic, Jurassic, Cretaceous, Tertiary, Quaternary
Ch 8 section 5 p. 338
1. Summarize the process by which scientists determined the age of Earth.
Radioactive dating of rocks from Earth and the moon
2. What physical features formed during Earth’s first several hundred million years?
Oceans, the atmosphere, and continents
3. How did volcanic eruptions and comets change early Earth?
They released carbon dioxide and water vapor into the atmosphere.
4. How would Earth’s atmosphere be different if organisms capable of photosynthesis had not evolved? Explain.
It would have little or no oxygen.
Ch 8 section 6 p. 342
1. How did Earth’s organisms change during the first period of the Paleozoic?
There was an invertebrate “explosion” as many new life forms appeared.
2. What event do scientists think may have caused the mass extinction at the end of the Paleozoic?
Climate change resulting from continental drift
3. How was their small size helpful to the mammals of the Mesozoic?
Mammals ate smaller organisms than themselves, such as insects, so they were not competing with dinosaurs for food.
4. Many scientists think that the asteroid impact at the end of the Cretaceous prevented plant growth for many years. Although many
dinosaurs were plant eaters, some were meat eaters. Develop a hypothesis to explain why no dinosaurs survived.
Plant-eating dinosaurs were food for the meat-eating dinosaurs. When the plant-eaters died out, there was no source of food for the
meat-eaters, so they also died out.
5. What conditions allowed so many different kinds of mammals to evolve during the Cenozoic Era?
Dinosaurs had become extinct, so it made way for the evolution of mammals. Grasses evolved, which provided food sources for
larger, grazing animals.
Study Guide for the Earth History Post Test
Test Date: Friday, 4 Dec
Ch 8 section 1 p. 318
1. In general, how does a fossil form?
2. Which parts of an organism are most likely to be preserved as fossils? Why?
3. What are two things that scientists can learn from the fossil record?
4. What does the fossil record show about how life has changed over time?
Ch 8 section 2 p. 325
1. In your own words, define the terms relative age and absolute age.
2. A geologist finds a cliff where the edges of several different rock layers can be seen. Which layer is the oldest? Explain using the
correct law.
3. Besides the law of superposition, what are three types of clues to the relative age of rock layers?
4. Compare and contrast extrusions and intrusions.
5. An intrusion crosses an extrusion. Which layer is the older? Explain.
6. The fossil record shows that horseshoe crabs have existed with very little change for about 200 million years. Would horseshoe
crabs be useful as an index fossil? Explain why or why not.
Ch 8 section 3 p. 331
1. How does the composition of a rock containing a radioactive element change over time?
2. What method do geologists use to determine the absolute age of a rock?
3. Why is it difficult to determine the absolute age of a sedimentary rock?
4. A geologist finds a fossil in a layer of sedimentary rock that lies in between two igneous extrusions. How could the geologist
determine the age of the fossil?
Ch 8 section 4 p. 335
1. What information did geologists use in developing the geologic time scale?
2. What are the basic units into which the geologic time scale is divided?
3. Study Figure 14. Which major division of geologic time was the longest?
4. Place the following in the correct order from earliest to latest: Tertiary, Jurassic, Quaternary, Triassic, Cretaceous.
Ch 8 section 5 p. 338
1. Summarize the process by which scientists determined the age of Earth.
2. What physical features formed during Earth’s first several hundred million years?
3. How did volcanic eruptions and comets change early Earth?
4. How would Earth’s atmosphere be different if organisms capable of photosynthesis had not evolved? Explain.
Ch 8 section 6 p. 342
1. How did Earth’s organisms change during the first period of the Paleozoic?
2. What event do scientists think may have caused the mass extinction at the end of the Paleozoic?
3. How was their small size helpful to the mammals of the Mesozoic?
4. Many scientists think that the asteroid impact at the end of the Cretaceous prevented plant growth for many years. Although many
dinosaurs were plant eaters, some were meat eaters. Develop a hypothesis to explain why no dinosaurs survived.
5. What conditions allowed so many different kinds of mammals to evolve during the Cenozoic Era?