?Throughout geologic time there have been several episodes of species extinction. Rank

What is relative dating?

A granitic dike is found across a sandstone layer. What can be said about the relative ages of the dike and the sandstone? What principle applies here?

Why don’t all rock formations show a continuous sequence from the beginning of time to the present?

How are fossils used in determining geologic time?

In a sequence of sedimentary rock layers, the oldest layer is on the bottom and the youngest layer is at the top. What relative dating principle applies here?

Explain how fossils of fishes and other marine animals are found at high elevations, such as the Himalayas.

What is a radioactive half-life?

What are the half-lives of uranium-238, potassium-40, and carbon-14?

What isotope is preferred for use in dating very old rocks?

What isotope is commonly used for dating sed

Which of the geologic time units spans the greatest length of time?

How old is Earth?

What key developments in life occurred during Precambrian time?

What evidence do we have of Precambrian life?

The Paleozoic era experienced several fluctuations in sea level. What effect did this have on life forms?

Name the periods of the Paleozoic era.

What life form emerged in the Silurian period?

What life forms are associated with the Devonian period?

Why are internal nostrils in the lobe-finned fishes an important step in the evolution of life on Earth?

Why do many geologists consider the lobe-finned fishes especially significant?

During what time period were most coal deposits laid down? Why was this period unique?

In what area of the United States do we find rich coal deposits?

What group evolved from the amphibians with the arrival of the amniote egg?

By what informal name is the Mesozoic era known?

What is the most likely cause of the Cretaceous extinction that wiped out the dinosaurs?

What effect did the breakup of Pangaea have on sea level?

How is the element iridium related to the time of dinosaur extinction?

Which epochs make up the Tertiary period? The Quaternary period?

What important life forms evolved during the Cenozoic era?

Refer to the accompanying figure. Using the principles of relative dating, determine the relative ages of the rock bodies and other lettered features. Start with this question: What was there first?

On a cross section, a dark wavy line is used to represent unconformities—missing layers of time. Match the following three types of unconformities—angular unconformity, nonconformity, and disconformity—to the diagrams below.

If fine muds were laid down at a rate of 1 cm/1000 yr, how long would it take to accumulate a sequence 1 km thick?

With the formation of Pangaea, disconnected continents merged into one huge landmass. This decreased the amount of shallow marine environments, which led to mass extinctions during the Permian. Let us compare the difference in coastlines for a single large landmass and a same-sized landmass that is broken up into several pieces. (a) Find the perimeter for each shape shown here. Then add all the perimeters together. b) Like Pangaea, the shapes are joined into one landmass. Find the perimeter of the single landmass. (c) Compare the total perimeters for parts (a) and (b). Do your results support the decrease in coastlines after the formation of Pangaea?

The decay of radioactive elements to stable elements can be used to “date” certain rocks and minerals. Going from dating oldest rocks to dating youngest rocks, rank the following radioactive elements: (a) carbon-14, (b) potassium-40, (c) uranium-238, (d) uranium-235.

Going from oldest to youngest, rank these life forms: (a) rat bones, (b) fossil ferns, (c) trilobites, (d) dinosaur bones.

The geologic time scale is subdivided into eons, eras, periods, and epochs. Rank, from oldest to most recent, the following time periods: (a) Cretaceous, (b) Jurassic, (c) Triassic, (d) Tertiary, (e) Permian.

Our Earth has experienced several episodes of glaciation. Going from the most recent episode of glaciation to the oldest episode, rank these time periods: (a) late Precambrian, (b) Pleistocene, (c) early Permian, (d) Ordovician.

Throughout geologic time there have been several episodes of species extinction. Rank the following from most devastating to least devastating: (a) Ordovician, (b) Permian, (c) Cretaceous, (d) Pleistocene.

Throughout geologic time there have been many changes to Earth’s surface. From most recent to the most distant past, rank these tectonic events: (a) formation of the Appalachian Mountains, (b) formation of Gondwanaland, (c) break up of Pangaea, (d) formation of the Gulf of California.

The Cenozoic is known for many tectonic events. In sequential order, from earliest to most recent, list the following events: (a) formation of the Gulf of California, (b) formation of the Himalayas, (c) birth of the San Andreas fault.

Each period of the Paleozoic saw marked changes in life forms. List the following life forms in the order in which they appeared on Earth during the Paleozoic: (a) reptiles, (b) fishes, (c) swamp forests, (d) terrestrial life, (e) vertebrates, (f) shelled organisms.

The Precambrian spans a huge amount of time. List the following highlights of the Precambrian from first to last: (a) stromatolites, (b) formation of the Moon, (c) appearance of primitive ozone layer, (d) formation of the oceans.

If a sedimentary rock contains inclusions of metamorphic rock, which rock is older? Defend your answer.

Granitic pebbles within a sedimentary rock have a radiometric age of 300 million years. What can you say about the age of the sedimentary rock? Nearby, a dike having a radiometric age of 200 million years intrudes into an outcrop of the same sedimentary rock. What can you say about the age of the sedimentary rock?

Two isolated rock outcrops share a few similar characteristics—sequence of layers, mineralogy, and certain fossil communities—but not all layers are present. The rocks are separated by 300 km. Could the two outcrops be related? How can you explain the missing layers?

Suppose that in an undeformed sequence of rocks, you find a trilobite embedded in a black shale layer at the bottom of the formation, and primitive vascular plant fossils embedded in a green shale at the top of the formation. From your observation, what can you say about the ages of the formation?

In a sequence of sedimentary rock layers, the youngest layer is found at the bottom and the oldest layer at the top. What does this type of layering signify?

What is the difference between a nonconformity and an angular unconformity?

Two isolated rock outcrops that share similar characteristics—sequence of layers and fossil communities—are separated by 50 km. Could these two outcrops be related? What principle helps to confirm their relationship?

What general assumption must be made to understand the processes that occurred throughout Earth’s history?

Suppose you see a sequence of sedimentary rock layers covered by a basalt flow. A fault displaces the bedding of the sedimentary rock but does not cut into the basalt. Relate the fault to the ages of the two rock types in the formation.

In dating a mineral, what is meant by “resetting the mineral’s time clock”?

A radiometric date is determined from mica that has been removed from a rock. What does the date signify if the mica is found in granite? What does the date signify if the mica is found in schist?

If we divide a number by 2, and then divide the result by 2, and so on indefinitely, the answer will never be zero. Why, then, is carbon dating useful only for materials that are no older than about 50,000 years? (Hint: What is the half-life of carbon-14?)

Which isotopes are most appropriate for dating rocks from the following ages: (a) early Precambrian time, (b) the Mesozoic era, and (c) the late Pleistocene epoch?

Has the amount of uranium in Earth increased over geologic time? Has the amount of lead in Earth increased?

Before the discovery of radioactivity, how did geologists estimate the age of rock layers?

In the geologic time scale, which time division represents the greatest span of time?

What is the basis for the divisions of the geologic time scale?

What factors are believed to have contributed to the generation of free oxygen during the late Precambrian? In what way did the increase in oxygen affect our planet?

Before entering the atmosphere, where did much of the newly released oxygen end up during the Precambrian?

Name the eons in Precambrian time. Describe each eon, using no more than three words.

How did the Precambrian atmosphere become nitrogen-enriched?

Why is it difficult to find fossils in Precambrian rocks?

What are stromatolites, and what is their significance in Earth’s history?

Geologists often refer to the early Paleozoic era as the Cambrian explosion. What do you think this term means?

Why are Paleozoic marine sedimentary rocks such as limestone and dolomite found widely distributed in the continental interiors?

Throughout the Paleozoic, sea level was variable; sometimes it was high and other times it was low. What was the primary cause of this variation in sea level?

What was the coldest period of the Paleozoic? What may have contributed to this cooling period?

During the Silurian, many continental landmasses were covered by shallow seas. Yet this time period marks the emergence of land plants. How can this be?

Coal beds form from the accumulation of plant material that has become trapped in swamp floors. Yet coal deposits are found on the continent of Antarctica, where no swamps or vegetation exists. What is your explanation?

In what ways can sea level be lowered? What effect might this have on existing life forms?

What can cause a rise in sea level? Is this likely to happen in the future? Why or why not?

What are some potential worldwide consequences that can occur when all landmasses are joined together, as in the formation of Pangaea?

What is the significance of an amniote egg?

How did the breakup of Pangaea impact land-based animal and plant life?

What effect did the breakup of Pangaea have on Earth’s climate?

Was there a time when dinosaurs and humans coexisted?

Most scientists think the iridium-rich sediments found straddling the Cretaceous–Tertiary boundary can be explained by a meteorite impact. Why are high concentrations of iridium significant?

Why does sea level rise when the rate of seafloor spreading increases?

How does basaltic lava in a rift zone separate two landmasses?

What impact did the breakup of Pangaea have on sea level?

What is the Anthropocene epoch?

How did Pleistocene climate affect land-based animals?

What was the impact on animal diversity as continents became separated from one another?

What event allowed the evolution of many mammals in the early Cenozoic era?

How did Pleistocene glaciations affect the land surface?

What is a likely cause of glacial–interglacial cycles? Are we currently in an ice age? Explain.

How was the Gulf of California formed?

What geologic event most likely resulted in the bending of the Hawaiian Island/Emperor Seamount chain?

How did the San Andreas Fault form?

How old are the oldest rocks on Earth? About how old are the oldest rocks on the Moon?

During Earth’s long history, life has emerged and life has perished. Briefly discuss the emergence of life and the extinction of life during each era.

If sea level were to rise today, what land areas would be most affected? What life forms would be in danger of extinction?

What circumstances are likely to lead to the formation of continental-scale glaciers?

How did the loss of coastlines affect shallow marine life? Could this happen again?

How have modern humans affected geologic processes?

Throughout geologic time, species have become extinct. Many scientists believe that Earth is presently experiencing one of the fastest mass extinctions of all time. This extinction is mainly the result of human activity. What are some possible effects of this dramatic loss of species?

Species can go extinct when they are unable to adapt to changes in the environment or compete effectively with other organisms. The cause of extinction can be catastrophic or natural. What are some possible examples of extinction? (Hint: Think celestial vs. terrestrial.)

What six principles are used in relative dating? Describe each one.