Chapter 25 Homework

Part E Which group of animals is currently facing the greatest threat from climate change?

corals

Part C You are a researcher studying a group of organisms that all disappeared during the Permian extinction. What do you study?

trilobites

Part A Which of the following would be LEAST likely in the fossil record?

desert-dwelling species

Part E Which of the following is true regarding your mitochondrial DNA?

It all came from your mother.

Part A The planet is currently facing its _____ mass extinction event.

sixth

Part A On the basis of their morphologies, how might Linnaeus have classified the Hawaiian silverswords? Linnaeus would have _____.

placed more of them in different genera than modern botanists do.

Part A Fossilized stromatolites

resemble structures formed by bacterial communities that are found today in some warm, shallow, salty bays.

Part A Many species of snakes lay eggs. However, in the forests of northern Minnesota, where growing seasons are short, only live-bearing snake species are present. This trend toward species that have live birth in a particular environment is an example of _____.

species selection

Part A The atmosphere of early Earth probably contained no O2 until the emergence of organisms that _____.

used water as an electron source for photosynthesis Oxygen began to accumulate in the atmosphere due to the action of photosynthetic cyanobacteria.

Part A Evolution works by _____.

"tinkering" with existing structures Evolution, and in particular natural selection, can only select for the best available traits. Modifications to those traits are usually made in small, incremental steps, and new inventions are rare.

Part A According to the theory of sea-floor spreading, oceanic islands, such as the Hawaiian Islands depicted in the figure above, form as oceanic crustal plates move over a stationary "hot spot" in the mantle. Currently, the big island of Hawaii is thought to be over a hot spot, which is why it is the only one of the seven large islands that has active volcanoes. What should be true of the island of Hawaii? 1. Scientists in search of ongoing speciation events are more likely to find them here than on the other six large islands. 2. Its species should be more closely related to those of nearer islands than to those of farther islands. 3. It should have a rich fossil record of terrestrial organisms. 4. It should have species that are not found anywhere else on Earth. 5. On average, it should have fewer species per unit surface area than the other six islands.

1, 2, 4, and 5

Part B - Radiometric dating The age of fossils can sometimes be determined by radiometric dating, which is based on the constant rate of decay of radioactive isotopes. The time required for half of a radioactive isotope to decay is called the half-life of that isotope. For example, the isotope carbon-14 has a half-life of 5,730 years. Suppose it is determined that a fossilized leaf contains 12.5% of the carbon-14 that was present when the fossil formed. How old is the fossil? Express your answer numerically.

17,190 years Radiometric dating is a technique for determining the age of fossils that is based on the fact that specific radioactive isotopes decay at a constant rate. Each isotope has a characteristic half-life, which is the time required for half of that isotope to decay. After one half-life has elapsed, 50% of the isotope has decayed and 50% remains. After two half-lives, 75% has decayed and 25% remains. After three half-lives, 87.5% has decayed and 12.5% remains. For carbon-14, which has a half-life of 5,730 years, three half-lives corresponds to 17,190 years.

Part A The questions below refer to the following description and figure. The figure below represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about one million years old, and potassium-40 dating is typically used to date such rocks. Note: The horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley. If a particular marine organism is fossilized in the sediments immediately overlying the igneous rock at the arrow labeled "II," at which other location, labeled A-E, would a search be most likely to find more fossils of this organism?

C

Part A The questions below refer to the following description and figure. The figure below represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about one million years old, and potassium-40 dating is typically used to date such rocks. Note: The horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley. Which section of sea-floor crust should have the thickest layer of overlying sediment, assuming a continuous rate of sediment deposition?

E

Part D Ancient American Indian skulls provide evidence that which of the following is true?

Europeans contributed to American Indian ancestry.

Part D As more carbon dioxide is added to the atmosphere, which of the following is most likely to happen?

Increasing ocean acidification and decreasing concentration of oxygen in the oceans.

Part A How does continental drift affect living organisms?

It causes climate change, which puts selective pressure on organisms. It causes changes in habitats, such as when large amounts of shallow marine habitat were lost in the formation of Pangaea. It may cause an increase or decrease in competition among different species. It happens so slowly that it does not affect living organisms. All but one of these are correct. Continental drift affects organisms by changing the current environment in all of these ways. Organisms may have to adapt, move, or go extinct.

Part A What is true of the fossil record of mammalian origins?

It includes transitional forms with progressively specialized teeth.

Part A A paleontologist finds a new tyrannosaur in a site she is excavating, and wishes to date the fossil. What is the most likely method she will use?

She will infer the age of the fossil by dating layers of volcanic rock above and below the stratum containing the fossil. Read how rocks and fossils are dated.

Part A What was the "oxygen revolution," which took place 2.3 billion years ago?

The "oxygen revolution" was the rapid increase in atmospheric oxygen that took place 2.3 billion years ago, dooming many prokaryotic groups. Read about photosynthesis and the oxygen revolution.

Fossil Record The fossil record provides a glimpse into the evolution of life on Earth. It shows that there have been remarkable changes in the kinds of organisms that have been abundant at different times during the past 3.5 billion years. Part A - The history of life according to the fossil record Classify each event in the history of life into the appropriate eon or era. Drag each phrase to the appropriate bin.

The figure below shows the geologic record as well as some important events in the history of life.

Likelihood of finding a fossil Only a very small percentage of organisms actually fossilize. Based on the information in the table below, rank the likely abundance of fossils of organisms A-E. Description Organism A Organism B Organism C Organism D Organism E soft body with no skeleton × × × × soft body covered by hard shell × lives where sediment is not being deposited × × lives near the shore of a river or ocean × × × large population and long existence × × × small population and short existence × × lives where oxygen content is low × × × lives where oxygen content is high × × Rank the fossils of organisms A-E from most common to least common. If two fossils have the same commonness, overlap them.

The fossil record presents an incomplete picture of the history of life because all species are not equally likely to leave fossils. Hard-shelled species that die where sediment is actively being deposited are most likely to fossilize, whereas soft-bodied species that die where they cannot be buried are rarely fossilized. Moreover, if a species is not abundant or does not exist for a long time, its fossils will likely be rare. Species that die in an environment with a low oxygen content are more likely to leave fossils because a low oxygen content inhibits decomposition.

You are an archaeologist and you find human remains with a mitochondrial DNA lineage of X. Which of the following is true?

The remains are American Indian or European.

Part B Why didn't the dinosaurs go extinct during the Permian extinction?

They weren't alive at that time.

Part A It is most strongly believed that the descendants of American Indians arrived in North America by doing which of the following?

Walking across the Beringian land bridge.

Part A Which of the following organisms would be most likely to fossilize?

a common squirrel

Part A A hypothetical island lies far from any other landmasses. There are many different types of plants, but only one animal, a beetle, that can fly or walk from plant to plant and feeds by chewing leaves. Given that the beetle is not exploiting all of the resources on the island, which morphological change would be most likely to trigger an adaptive radiation of the beetles?

a mouthpart that can pierce fruits and seeds

Part A Upon being formed, oceanic islands, such as the Hawaiian Islands, should feature what characteristic, leading to which phenomenon?

a variety of empty ecological niches, leading to adaptive radiation

Part A Radiometric dating _____.

allows us to indirectly date fossils up to billions of years old based on minerals in surrounding volcanic strata By dating minerals in volcanic strata above and below the fossils, we can determine a reasonable age range for the fossils.

Part A The oldest fossils usually _____.

are found in the deepest strata Younger sediments are deposited over older sediments; thus, relatively older fossils are found in deeper strata than relatively younger fossils.

Part A Hawaii is the most southeastern of the seven largest islands and is also closest to the sea-floor spreading center from which the Pacific plate originates, which lies about 5600 km further to the southeast. Assuming equal sedimentation rates, what should be the location of the thickest sediment layer and, thus, the area with the greatest diversity of fossils above the oceanic crust?

around the base of Kauai, the oldest of the large Hawaiian islands

Part A If a fossil is encased in a stratum of sedimentary rock without any strata of volcanic rock (for example, lava or ash) nearby, then it should be _____.

difficult to determine the absolute age of the fossil, because radiometric dating of sedimentary rock is less accurate than that of igneous rock

Part C You are a geneticist studying the random changes in burrowing owl DNA from one generation to the next. What are you researching?

genetic drift