Mastering Geology Geologic Time and Fossils

10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils 7-2 MasteringGeology: Geologic Time and Fossils Due: 6:59am on Monday, October 24, 2022 You will receive no credit for items you complete after the assignment is due. Grading Policy SmartFigure: Relative Dating Launch the SmartFigure Video When you have finished, answer the questions. Part A A sandstone contains inclusions of metamorphic rock. An igneous dike cuts both the sandstone and inclusions. List the rocks from youngest to oldest. Hint 1. Use your knowledge regarding the principles of cross-cutting relationships and dating by inclusions to answer this question. ANSWER: metamorphic rock, igneous dike, sandstone sandstone, metamorphic rock, igneous dike metamorphic rock, sandstone, igneous dike igneous dike, sandstone, metamorphic rock igneous dike, metamorphic rock, sandstone Correct Part B If a sequence of sedimentary units is cut by a fault, what does the principle of cross-cutting relationships tell a geologist? Hint 1. Recall what the principle cross-cutting relationships states and how it is used for relative age dating. ANSWER: Sedimentary layers are laid down horizontally. The oldest sedimentary unit is located at the base of the sequence, while the youngest is at the top. All of the sedimentary units must have been deposited and lithified before being cut by the fault. The sedimentary units on the left side of the fault are the same as those on the right side. The fault is older than the sedimentary sequence. Correct Part C 1/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils Which of the following describes the principle of original horizontality? Hint 1. The video showed a sequence of folded sedimentary rocks. What had to occur to form this feature? ANSWER: A fault or dike that cut a sedimentary sequence is younger than the sedimentary rocks it breaks through. The oldest sedimentary unit is located at the base of the sequence, while the youngest is at the top. Undeformed sedimentary layers present on one side of a river-cut canyon are the same as those on the opposite side. Inclusions within a sedimentary rock are older than the sedimentary rock itself. Folded sedimentary layers were originally laid down flat and later deformed. Correct Part D An undeformed sequence of sedimentary rocks is exposed in a large river canyon. Which two principles would be demonstrated by the rocks? Hint 1. Think back to the five principles you learned about in the video. Which two would be the most applicable to an undeformed rock sequence that has been eroded by a large stream? ANSWER: principles of cross-cutting relationships and superposition principles of superposition and lateral continuity principles of lateral continuity and inclusions principles of lateral continuity and cross-cutting relationships principles of superposition and dating by inclusions Correct Part E An igneous dike cuts through limestone, but not through the overlying sandstone. Which of the following statements is most accurate? Hint 1. Think about how the principles of superposition and cross-cutting relationships are used for this question. ANSWER: First, the sandstone was laid down, next the limestone was deposited, and finally was cut by the igneous dike. First, the limestone was laid down, folded and cut by an igneous dike, and finally the sandstone was deposited. First, the limestone was laid down, then intruded by the igneous dike, and lastly the sandstone was deposited. The limestone and sandstone were deposited and then cut by the igneous dike. The igneous dike represents the oldest rock, while the sedimentary rocks are relatively younger. Correct GeoTutor: Constructing an Order of Sequence of Geologic Events—Relative Dating 2/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils The ordering of events in geological history has long been a difficult task but once simple principles were determined, observation and logic could be used to determine the order of events. With these principles, one cannot calculate the exact number of years ago an event occurred, but instead the sequence of events can be determined. This is referred to as relative dating. The principles are as follows: 1. The principle of superposition: In sedimentary rocks, the rock bed on the bottom must be older than the rock bed on the top. 2. The principle of original horizontality: Sedimentary rocks were originally deposited as flat-lying, horizontal layers. 3. The principle of cross-cutting relationships: Any rock or feature cutting through another rock or feature must be younger than the material through which it cuts. (For example, with faults, the first rock must be there for these secondary features, such as igneous intrustions like dikes or fractures, to cut through.) 4. Inclusions: Any rock fragments included within another rock must be older than the rock in which they are included. (For example, if eroded fragments of one rock layer become part of another sedimentary rock layer, the rock with the included fragments must be younger than the fragments themselves.) Part A - Basic Principles for Relative Geologic Dating Below is a geologic structure that illustrates the various principles of relative dating. You will identify the basic principles used in relative geologic dating by dragging labels to their corresponding targets in the image below. Drag the appropriate labels to their respective targets. Hint 1. Inclusions in sedimentary rock layers According to the principle of inclusions, the layer of rock that has inclusions from another rock layer must be younger. Hint 2. A dike cutting through sedimentary rock layers The rock layers that the dike cuts through must have been there first. This is the principle of cross-cutting relationships. ANSWER: Reset Help Principle of Superposition Principle of Inclusions Principle of Crosscutting Relationships Correct As you can see from above, we can determine a sequence of events using the logic of these principles when observing sedimentary rock. Now that we have investigated the principles of relative dating, we can use these principles to determine how to read the sequence of geologic events in a location. Part B - Ordering of Geologic Events The principles of relative dating can be used to understand the order of geologic events. A geologic event can be anything: the deposition of horizontal layers of sedimentary rock, the faulting or folding of rock layers, the tilting of rock layers, the erosion (or wearing away) of rock, the intrusion of volcanic rock within existing rock layers, and so on. Refer to these relative dating principles: Inclusions: Any rock fragments included within another rock must be older than the rock in which they are included. (For example, if eroded fragments of one rock layer become part of another sedimentary rock layer, the rock with the included fragments must be younger than the fragments themselves.) The Principle of Cross-cutting Relationships: Any rock or feature cutting through another rock or feature must be younger than the material through which it cuts. (For example, with faults, the first rock must be there for these secondary features, such as igneous intrustions like dikes or fractures, to cut through.) Tilting or deformation could occur to an otherwise horizontally layered sedimentary rock. Most layers of sediment are deposited in a nearly horizontal position. Thus, when we see rock layers that are folded or tilted, we can assume that they must have been moved into that position by crustal disturbances after their deposition. In such an instance, the tilted structure will be younger than the orginal horizontal layers. 3/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils Order the four images below along the timeline based on the sequence of geologic events. Rank from oldest to youngest. Hint 1. Inclusions from rock layers above and below In the picture where the gray layer first appears, the layer must be younger than the layers above and below because it has inclusions of both layers of rock within it according to the principle of inclusions. Therefore, this event must have happened after the picture without the gray layer. This can occur when igneous rock intrudes between layers of sedimentary rock and incorporates pieces of the rock layers above and below into the cooling magma. Hint 2. The oldest and the youngest geologic features/events The oldest geologic feature should have the least geologic changes and the youngest should have all features from the previous events. ANSWER: Reset Help Correct You can apply the logic of the principles of relative dating to successfully sequence the order of geologic events in a scene. These principles allow you to tell the geologic story of a landscape. SmartFigure: Fossil Ranges Launch the SmartFigure Video When you have finished, answer the questions. Part A What is the best definition of fossil range? 4/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils Hint 1. Think about what you learned about fossil organisms and how they are important to constrain a rock’s relative age. ANSWER: The geographic area over which an organisms thrives. The variety of organisms that occur together in a rock unit. The time when an organism goes extinct. The period of time when an organism first and last appears in the sedimentary record. The total number of organisms alive at one time in the geologic record. Correct Part B Which of the following characteristics is the most desirable for constraining the relative age of rocks? Hint 1. Relate this question to what you learned regarding fossil range. ANSWER: organisms with overlapping ranges and geologically short lifespans organisms that overlap in range and are geologically long-lived organisms that do not overlap in range organisms that are soft-bodied and microscopic in size organisms that span long periods of geologic time Correct Part C Which organism from the video is the least useful for relative dating? Hint 1. Think back to each organism’s range in rock units A and B. Which organism was not helpful in bracketing an age? ANSWER: trilobite dinosaur sycamore leaf scallop fern Correct Part D If a rock contains ten different kinds of fossils, which of the following must be true? Hint 1. To help answer this question, recall rock units A and B and their specific fossil assemblages shown in the video. 5/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils ANSWER: All ten organisms evolved at the same time. These organisms give the minimum age of the rock. All ten organisms went extinct at the same time. All of the organisms had to be alive when the rock was deposited. All of the fossils are useful in constraining relative age. Correct Part E How is the geologic time scale related to the fossil record? Hint 1. Think about the connection between fossils and bracketing the age of a sedimentary rock. ANSWER: The time scale is only built on times when organisms went extinct. Radiometric dating of organisms was used to build the time scale. The periods of the time scale were constructed based on ranges of fossil organisms. The fossil record is not related to the geologic time scale. The Precambrian was defined using fossil organisms. Correct SmartFigure: Half Life Launch the SmartFigure Video When you have finished, answer the questions. Part A Which of the following includes all common types of radioactive decay? Hint 1. Three types of radioactive decay were mentioned at the beginning of the movie. Each type of decay influences the atomic number of an atom. ANSWER: 6/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils alpha particle emission, beta particle emission, electron capture alpha particle emission, beta particle emission, half-life atomic number, beta particle emission, electron capture alpha particle emission, beta particle emission, radioactive parent isotope alpha particle emission, stable daughter, electron capture Correct Part B Which of the following statements regarding radioactive decay is true? Hint 1. Think about the process of radioactive decay and what happens over time. ANSWER: The number of half-lives decreases over time. More daughter products accumulate over time. The nucleus of a radioactive particle is not affected. More parent isotopes accumulate over time. A mineral starts out with a parent:daughter isotope ratio of 75:25. Correct Part C If one half-life has lapsed, what is the radioactive parent to stable daughter isotope ratio? Hint 1. The answer is true for the breakdown of all radioactive isotopes. ANSWER: 13:87 75:25 6:94 50:50 25:75 Correct Part D Radioactive decay in mineral shows that two half-lives have elapsed, giving an age of approximately 1.4 billion years. Using the table in the video as a reference, what is the correct radioactive parent and stable daughter isotope pair? Hint 1. Use what you learned in the video and the textbook to answer this question. ANSWER: 7/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils Rb87, Sr87 Th232, Pb208 K40, Ar40 U238, Pb206 U235, Pb207 Correct GEODe: Dating with Radioactivity Launch the GEODe video and when you have finished, answer the questions. Part A How is the atomic number of an atom determined? Hint 1. How is atomic number different than atomic mass? ANSWER: counting the number of protons circling the nucleus counting the number of protons in the nucleus counting the number of atoms of an element in a mineral counting the number of protons and neutrons in the nucleus counting the number of neutrons in the nucleus Correct Correct! The atomic number for carbon is 6 because it has 6 protons in the nucleus. Part B Which process is not a common form of natural radioactive decay? Hint 1. Review the various ways in which radioactive isotopes decay to form daughter isotopes. ANSWER: emission of alpha particles emission of beta particles electron capture nuclear fission 8/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils Correct Correct! Nuclear fission occurs when the nucleus of an atom splits into two or more smaller nuclei and neutrons are released. This process occurs exceptionally slowly and rarely in nature, and only among the elements with very high atomic numbers. Part C Which material, principle, or process enables a method of numerical dating? Hint 1. Numerical dating techniques are sometimes called “absolute dating,” as they provide the age of a material without having to reference any other related material. ANSWER: inclusions superposition radioactivity cross-cutting fossils Correct Correct! Using the decay rates of various radioactive elements, you can determine a numerical age for minerals in igneous rocks. The resulting date is called a “radiometric age.” Part D Which is an example of radioactivity that occurs when a neutron is converted to a proton and an electron is emitted from the nucleus? Hint 1. An emitted electron has a specific name. ANSWER: emission of an alpha particle nuclear fission emission of a beta particle magmatic fractionalization electron capture Correct Right! An atom can undergo radioactive decay by the loss of an electron from the nucleus and the conversion of a neutron to a proton, as in the decay of Thorium-234 to Protactinium-234. This process is called beta emission. Part E After four half-lives of decay, what is the ratio of radioactive parent isotope to stable daughter isotope? Hint 1. The same proportion (percentage) of parent isotope decays in each half-life. What changes over time is the physical amount of parent isotope remaining in the sample, relative to the physical amount of daughter isotope that has been produced. ANSWER: 9/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils 1:15 1:7 1:1 1:31 1:3 Correct Correct! After the passing of four half-lives, the amount of radioactive parent isotope left would be 1/15, or 6.66 percent, of the original amount and its age would be four times the value of the half-life. Part F A radioactive element undergoes decay via the loss of two alpha particles to form a stable daughter isotope. Following the decay, what would the atomic number of this newly created stable isotope be? Hint 1. What are the components of an alpha particle? For each alpha particle emitted, how does the atomic number change? ANSWER: The atomic number of the daughter isotope would be eight units less than the original parent isotope. The atomic number of the daughter isotope would be four units less than the original parent isotope. The atomic number of the daughter isotope would be 16 units less than the original parent isotope. The atomic number of the daughter isotope would be two units less than the original parent isotope. The atomic number of the daughter isotope would be four units more than the original parent isotope. Correct Correct! Because an alpha particle consists of 2 protons and 2 neutrons, the parent isotope would lose a total of 4 protons, causing the atomic number to decrease by 4. GeoTutor: Constructing an Order of Sequence of Geologic Events—Dating with Radioactivity—2 You probably have read or seen stories about archeological findings that include organic remains of a 1000-year-old mummy or an ancient weapon made from stone, which is an inorganic material. Geologists and paleontologists calculate the age of these organic (contain carbon) and inorganic (do not contain carbon) materials by radiometric dating using the isotopes C-14 and U-235, respectively. 1. C-14 dating: This process is often known as radiocarbon dating. It is used to determine both historical and recent events of archeological artifacts of biological origin such as bone, cloth, wood, and plant fibers. 2. U-235 dating: This is used to determine the age of inorganic substances such as ancient rocks and minerals. Part A - Calculating the Age of a Fossil Based on the Number of Half-lives Elapsed Each isotope has a unique half-life. The half-life of an isotope is the time taken for half of the starting quantity to decay (with a ratio of 1:1). After two half-lives, there will be one-fourth of the original parent sample and three-quarters would have decayed to the daughter product (with a ratio of 1:3). After three half-lives, the ratio becomes 1:7, and so forth. 10/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils The graph, for instance, shows that assuming the half-life of a sample is 4 months, then in 4 months, there will be 0.5 gram of the parent element and 0.5 gram of the daughter element will be produced. In month 8 (which is two-half-lives), there will be only 0.25 gram of parent element left and 0.75 gram of daughter element; that is, one-fourth of the parent sample (in red) is left, and in month 12, there is only one-eighth of the parent element. You attend a geology lab where you are asked to estimate the age of a fossil. The ratio of parent to daughter elements in the fossil sample is 1:7. You know that fossils are the remains of living organisms, which have some amount of C-14 isotope. The C-14 isotope, which has a half-life of 5730 years, begins to decay as the organism dies. What would be your estimation of the fossil's age? Hint 1. What a ratio of 1:7 means in terms of number of half-lives Recall that a parent–daughter ratio of 1:7 means three half-lives have elapsed. Hint 2. How to calculate the age of the given sample You can calculate the age of the given sample by following these steps: 1. Determine the number of half-lives elapsed equivalent to a parent–daughter ratio of 1:7. 2. Now, multiply the number of half-lives elapsed with the half-life (5730 years) of the radioactive element to calculate the age of the sample. Hint 3. The age of the fossil after three half-lives If, after one half-life, the fossil is 5730 years old, consider how the years will multiply after three half-lives. Alternatively, if 1 half-life = 5730 years, then 3 half-lives = ? years. ANSWER: 17,190 40,110 22,920 11,460 5730 2865 Correct When a living organism dies, it stops taking in new carbon. The ratio of C-12 to C-14 at the moment of death is the same as every other living organism, but the C-14 decays and is not replaced. The C-14 has a half-life of 5730 years, whereas the amount of C-12 remains constant in the sample. By looking at the ratio of C-12 to C-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a fossil. Part B - Radiometric Dating of Organic and Inorganic materials John is assisting a geologist who has traveled across the world and collected a few samples. He asks John to classify the samples that can be dated using carbon-14 and uranium235 (or U-235). All organic materials contain carbon and are dated using C-14; inorganic materials are dated using any radioactive element, such as uranium, rubidium, potassium, and thorium, except carbon. Now, help John group the samples. Drag the appropriate items to their respective bins. Each item may be used only once. Hint 1. How to approach the problem The following steps can be used to group the samples: 1. Identify organic and inorganic materials in the given samples. 2. Recall that organic samples are dated using C-14 and the inorganic samples are dated using U-235. Hint 2. What organic and inorganic materials are Organic materials contain carbon. Organic materials include all living things and remains of humans, plants, and animals. 11/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils Examples are paper made from plants and the remains of animals such as bones and teeth. Inorganic materials do not contain carbon as the principal element. Inorganic substances include rocks and minerals. Examples are gem stones and sand. Hint 3. Volcanic ash and gneiss Volcanic ash consists of fragments of pulverized rock. Gneiss is also a metamorphic rock. Consider if a rock is organic or inorganic in nature. Hint 4. What an Egyptian mummy is An Egyptian mummy is the preserved corpse of a human. The method of preserving a dead body by ancient Egyptians by embalming and wrapping is called mummification. ANSWER: Reset wood piece Egyptian mummies gneisses volcano ash Help granite Correct GEODe: Geologic Time Scale Launch the GEODe video and when you have finished, answer the questions. Part A Which represents the correct sequence from oldest to most recent or current eras on the Geologic Time Scale? Hint 1. The prefix meso- means middle. What does paleo- mean? (Think about what paleontologists study.) ANSWER: Cenozoic, Paleozoic, Mesozoic Cenozoic, Mesozoic, Paleozoic Paleozoic, Mesozoic, Cenozoic Mesozoic, Cenozoic, Paleozoic Paleozoic, Cenozoic, Mesozoic 12/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils Correct Correct! On the Geologic Time Scale, the Paleozoic represents the oldest era and includes organisms that are least similar to those seen today. It is followed by the Mesozoic and then the Cenozoic. Part B Which eon translates to “visible life” from the Greek? Hint 1. The only way life is directly “visible” in the rock record is through the fossils. When did life on Earth become sufficiently complex to begin leaving abundant fossil traces? ANSWER: Pleistocene Proterozoic Phanerozoic Paleozoic Archean Correct Correct! Phanerozoic means “visible life” when translated from Greek. The Phanerozoic represents the last 542 million years of geologic time and contains abundant fossils with hard skeletal parts. Part C Which is the shortest interval of geologic time? Hint 1. A good way to remember this subdivision might be: “smallest of three, only this e comes before p.” ANSWER: period era epoch eon Correct Correct! Of epochs, periods, eras, and eons, epochs are the smallest intervals of geologic time. The spelling of “epoch” (e before p) might help you remember this relationship. Part D The subdivisions of the Geologic Time Scale were based on which criteria or characteristics? Hint 1. If Proterozoic means “former life” and Mesozoic means “middle life,” what seems to be a common theme among various sections of the time scale? ANSWER: the order in which they were discovered radiometric dating types of rock within the units alphabetic order of the units types of fossils within the units 13/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils Correct Correct! The units on the Geologic Time Scale were defined using the first occurrence and last appearance of different kinds of organisms. Part E While working in the field, you find some sedimentary rocks that include hundreds of fossils of crinoids, numerous brachiopods, and a few trilobites. Realizing that these ancient organisms are some of the first with hard parts, and (when taken as a group) are not very similar to animal communities living today, in which unit of geologic time would you place these rocks? Hint 1. The fossil assemblage in this rock is particularly informative. Think about both the types of fossils and their relative abundance. When would all three of these organisms have co-existed in such numbers? ANSWER: the Precambrian the Paleozoic the Cenozoic the Phanerozoic the Mesozoic Correct Right! Crinoids, brachiopods, and trilobites have hard parts and they are not similar to organisms that are living today. They typify the marine life of the Paleozoic era. Give It Some Thought: Biodiversity and Mass Extinction Events through Geologic Time Throughout Earth’s history, the desire to eat or to avoid being eaten is a driving force in evolving better defenses, more intelligence, and increased speed. Species that are best adapted to the current environment thrive. Less adapted species must reside at the fringes of habitats, or become extinct if they are particularly poorly adapted. Catastrophic events, such as climate change or meteor impacts, rapidly change environment conditions. Several catastrophic events have occurred in Earth’s history that are evidenced in the geologic record as sudden shifts in the proliferation of certain fossils, and supported by chemical dating analyses. These events had global repercussions, giving species that once lived on the fringe an opportunity to spread throughout their habitat and beyond. Extinctions are typically named after the period(s) during which they occurred. Now, let’s focus on when these events happened. Part A - The order of important events in geologic time The Cambrian explosion describes the appearance of thousands of new species about 542 million years ago. Greater competition among species following the Cambrian explosion led to more rapid adaptation. Certain adaptations led to the origin of amphibians that brought life onto land. A meteorite impacts the dominant species. At about 65 million years ago, a carbonaceous meteorite impacted Earth, blocking out the Sun, and causing plants to die and temperatures to drop. This impact led to the extinction of many species, as well as the dinosaurs. As Earth recovered from the impact, mammals were able to take over. In the Tertiary period, the diversity of mammal species grew as the group proliferated. However, in the late Pleistocene, the earliest part of the Quaternary period, the larger mammal species, such as mammoths and mastodons became extinct. At the beginning of the Quaternary period, the first humans began to evolve. 14/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils Conditions on Earth influenced evolution and how biodiversity changed through time. Place the following events in order from earliest to most recent. Rank from first to last. Hint 1. Events that followed when a large carbonaceous meteorite hit Earth Scientists believe that the impact of a large carbonaceous meteorite caused the dinosaurs to become extinct. Mammals, birds, insects, and flowering plants flourished in the Cenozoic era that followed this impact and mass extinction. Hint 2. The Cambrian explosion The Cambrian explosion is used to describe the appearance of thousands of new species as evidenced by the sudden shift from a sparse fossil record to a fossil record that suddenly contains evidence of thousands of creatures, including all major invertebrate species. Hint 3. The rise of mammals The carbonaceous meteorite that impacted Earth 65 million years ago led to the extinction of the dinosaurs. Mammals at this time were preyed upon by dinosaurs and other animal groups that proliferated prior to the meteorite impact. Mammals were able to spread and diversify following the extinction or general decline of predators. ANSWER: Reset Cambrian explosion dominance of amphibians Earth hit by a large carbonaceous meteorite diversification and dominance of mammals Help extinction of giant mammals like mastodons Correct The Cambrian explosion occurred about 542 million years ago. The first amphibians moved to land in the late Devonian period, approximately 380 million years ago. Earth was hit by a large carbonaceous meteorite about 65.5 million years ago at the KT boundary. This led to the extinction of the dinosaurs and set the stage for the diversification and dominance of mammals in the Tertiary period. Most recently, in the late Pleistocene, giant mammal species became extinct. Now let’s focus on the repercussions of these events upon biodiversity. Part B - Events through geologic time that contributed to biodiversity Though life existed before the Cambrian explosion, it was likely not present with the same diversity. Life in the oceans was incredibly active before the first species began to move onto the continents. After the Cambrian explosion, the number of species in oceans greatly increased. Greater competition among species led to more rapid and advanced adaptations to escape predators. Adaptations also led to the origin of amphibians and plants, leading the habitation of land. Amphibians were able to move into swampy regions and tidal pools, escaping predators and exploring new habitats. Similarly, plants faced new challenges moving onto land, including coping with wind and gravity without the support provided by ocean water, but ultimately thriving and evolving into large trees. A drier period, the Paleozoic Era, resulted in vast changes of land plants and animals. Green algae require freestanding water to survive and are ancestors of modern plants. Early in this era, the first plants appeared on land that did not require freestanding water. A group of plants, called the gymnosperms, proliferated later in the era because their seeds were well adapted for the drier environment of the time. The drier climate was problematic for amphibians because they must return to water to lay their eggs. This was an opportunity to gain a competitive advantage for a new group: the reptiles. The eggs of reptiles have a shell, allowing them to be laid on land, which was a primary factor in the spread of these animals. Then, the Great Permian Extinction occurred. This extinction was likely the result of global warming associated with volcanism. Estimates of extinction are 90 percent of marine species and 70 percent of terrestrial species. The warming would have allowed anaerobic bacteria to thrive, putting large amounts of hydrogen sulfide into the atmosphere. This extinction paved the way for the dinosaurs, who thrived during the Triassic, Jurassic, and Cretaceous periods, until the KT boundary (Cretaceous–Tertiary boundary). 15/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils The timing of the KT boundary coincides with the carbonaceous meteorite impact that lead to the extinction the dinosaurs. Examine the illustration below and label the events that contributed to the diversity of life and evolution. Drag the appropriate labels to their respective targets. Hint 1. The first amphibians The first amphibians adapted from fish due to the growing challenges of life in the sea. They took advantage of many large tropical swamps that existed during the late Paleozoic to move further inland. Amphibians were successful because they began to move out of the water, opening up new territories. However, they were still closely tied to the water, in part because their eggs were laid and hatched in the water. ANSWER: Reset Help Increased predation meant adaptations: bigger brains, development of acute senses, and faster mobility. Appearance of this group allowed travel from swamp to land. Plants adapted to drier climates. Seeds were fertilized without freestanding water. This group's shell-covered eggs allowed offspring to be born outside of the water. Green algae were ancestors of this organism. It had restricted mobility and size. The Great Permian Extinction occurs, causing loss of many marine and terrestrial vertebrate species. Dinosaurs and many other species become extinct. 16/17 10/13/22, 3:06 PM 7-2 MasteringGeology: Geologic Time and Fossils Correct Biodiversity changed throughout geologic time. The changing environments and extinction events allowed different species to thrive at different times and adapt to new conditions. Increased predation in the sea lead to more rapid adaptations and allowed many species of fish to flourish. The first vascular plants to live on land had restricted mobility and size. The first amphibians traveled from swamp to land. Gymnosperms were adapted to drier climates and had seeds that could be fertilized without freestanding water. The shell-covered eggs of the first reptiles allowed their offspring to be born outside of the water. The Great Permian Extinction occurred during the Permian Period. Dinosaurs and many other species became extinct at the KT boundary. Now, let’s look closer at mass extinctions in Earth’s history. Part C - Past events of mass extinction Mass extinction events had a great effect on Earth and the organisms that inhabited it. Read the sentences below, and fill in the blanks to make them complete and correct. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is complete before submitting your answer. Note that some terms will remain unused. Hint 1. How extinctions are named and described Extinctions are often named for the period during which they occurred. They can be global, disrupt large ecosystems, and are often described in regards to the species that went extinct, and what species became prevalent afterwards. Species that become extinct leave unfulfilled niches in ecosystems that cause long lasting changes. ANSWER: Reset A carbonaceous meteorite Help may have caused a global cooling event as suspended dust blocked the Sun. Without the Sun's energy, many plants would have died. Without plants to feed on, many creatures would also have died. The KT boundary marks the timing of the extinction event tied to the demise of the dinosaurs and is visible in the rock record as a thin layer of sediment that can be found worldwide. The extinction of the dinosaurs was likely the result of rapid climate changes associated with the impact of a large carbonaceous meteorite. Mammals Volcanism thrived in the millenia following the extinction at the KT boundary. may have caused global warming, which would have warmed the oceans, decreasing the amount of dissolved oxygen and increasing the number anaerobic bacteria present in the ocean. These bacteria would have generated massive amounts of toxic hydrogen sulfide, leading to the Great Permian Extinction. The Great Permian Extinction was a massive extinction event in which 90 percent of marine life and 70 percent of vertebrate land species were wiped out, creating niches that dinosaurs would eventually fill. Correct A carbonaceous meteorite may have caused a global cooling event as suspended dust blocked the sun. The KT boundary is the extinction event tied to the demise of the dinosaurs. The extinction of the dinosaurs was likely the result of rapid climate changes associated with a large carbonaceous meteorite. Mammals thrived in the millennia following the extinction at the KT boundary. Volcanism may have caused global warming, eventually leading to the Great Permian Extinction. This was a massive extinction event in which 90 percent of marine life and 70 percent of vertebrate land species were wiped out. When a species goes extinct, it often creates room for new species to evolve. Sometimes, different animals will even evolve to fill the same niche in different regions. Score Summary: Your score on this assignment is 99.3%. You received 29.8 out of a possible total of 30 points. 17/17