19.3 arth s arly History Lesson bjectives dentify some of the hypotheses about early arth and the origin of life. xplain the endosymbiotic theory. xplain the significance of sexual reproduction in evolution. Lesson Summary he Mysteries of Life s rigins arth s early atmosphere contained toxic gases. he atmosphere also contained little or no oxygen. n the 1950s, Stanley Miller and Harold Urey set out to determine if organic molecules could assemble under eartly arth conditions. hey filled a container with water and gases that they thought represented the composition of arth s early atmosphere. hey passed electric sparks through the mixture to simulate lightning. Soon, organic compounds formed. he experiment showed that molecules needed for life could have arisen from simpler compounds. Under some conditions, large organic molecules form tiny bubbles called proteinoid microspheres. Structures similar to proteinoid microspheres might have become the first living cells. RN and DN also could have evolved from simple organic molecules. he first known life forms evolved about 3.5 billion years ago. hey were single celled and looked like modern bacteria. ventually, photosynthetic bacteria became common. During photosynthesis, the bacteria produced oxygen. he oxygen accumulated in the atmosphere. he rise of oxygen drove some life forms to extinction. t the same time, other life forms evolved that depended on oxygen. rigin of ukaryotic Cells he first eukaryotes, or organisms with nuclei, evolved from prokaryotes that began to develop internal cell membranes. ne explanation for how eukaryotes evolved is the endosymbiotic theory. his theory proposes that smaller prokaryotes began living inside larger cells and evolved a symbiotic relationship with the larger cells. Sexual Reproduction and Multicellularity Sexual reproduction evolved after eukaryotic cells. Sexual reproduction increased genetic variation, so evolution could occur more quickly. Several hundred million years after sexual reproduction evolved, multicellular life evolved. he Mysteries of Life s rigins 1. What are protenoid microspheres? hey are tiny bubbles formed from large organic molecules that have some characteristics of living cells. 2. Why do scientists think that RN may have evolved before DN? xperiments show that small sequences of RN could have formed and replicated on their own in the conditions present on early arth. Lesson 19.3 Workbook Copyright by Pearson ducation, nc., or its affiliates. ll Rights Reserved. 307
Use the diagram of the Miller-Urey experiment to answer Questions 3 5. Mixture of gases simulating atmosphere of early arth Spark simulating lightning storms Condensation chamber Water vapor Cold water cools chamber, causing droplets to form Liquid containing amino acids and other organic compounds 3. Label the diagram to show which part of Miller and Urey s apparatus simulated lightning storms on early arth. 4. What was the purpose of Miller and Urey s experiment? to determine whether organic molecules could assemble under the conditions of early arth 5. xplain the results of the Miller-Urey experiment. What did these findings suggest? he experiment produced several amino acids, which suggested that mixtures of organic compounds could have arisen from substances found on early arth. vidence now suggests that the composition of arth s early atmosphere was different from the one used in their experiment. However, more recent experiments with different mixes of gases have produced similar results. rigin of ukaryotic Cells 6. xplain the endosymbiotic theory. he endosymbiotic theory proposes that prokaryotic cells entered early eukaryotic organisms. ver time a symbiotic relationship evolved between primitive eukaryotic cells and the prokaryotic cells within them. Lesson 19.3 Workbook Copyright by Pearson ducation, nc., or its affiliates. ll Rights Reserved. 308
7. Draw the step in the endosymbiotic theory that shows the origin of chloroplasts. Label the structures in your drawing. ncient erobic Prokaryote ncient naerobic Prokaryote Nuclear envelope evolving Primitive erobic ukaryote Mitochondrion Students should draw ancient photosynthetic bacteria moving into a primitive eukaryotic cell and becoming chloroplasts, making the cell photosynthetic. nimals, fungi, and non-plantlike protists Plants and plantlike protists Primitive Photosynthetic ukaryote Sexual Reproduction and Multicellularity 8. How did sexual reproduction speed up the evolutionary process? Sexual reproduction shuffles and reshuffles genes in each generation. his increase in genetic variation greatly increases the chances of evolutionary change due to natural selection. 9. What is the most likely cause of the great amount of diversity currently seen in multicellular life forms? arly multicellular life most likely underwent a series of adaptive radiations. 10. nce DN evolved, what could have caused it to become the primary means of transmitting genetic information instead of RN? SMPL NSWR: DN was a more stable information-storing molecule than RN. Lesson 19.3 Workbook Copyright by Pearson ducation, nc., or its affiliates. ll Rights Reserved. 309
Chapter Vocabulary Review Crossword Puzzle Complete the puzzle by entering the term that matches the description. cross 1. time span shorter than an era 2. fossil used to compare the relative ages of fossils and rock layers 7. theory that eukaryotic cells arose from communities of several prokaryotes 9. measures evolutionary time: geologic time 10. span of geologic time that is subdivided into periods 11. the time required for half of the radioactive atoms in a sample to decay 12. a species dying out because of the slow but steady process of natural selection: background Down 1. scientist who studies fossils 3. describes a species that no longer exists 4. method used to place rock layers and their fossils in a time sequence (2 words) 5. the process by which a species or group of species evolves into several different forms that live in different ways: radiation 6. process by which two species evolve in response to changes in each other over time 8. disappearance of many species at the same time: extinction 1 2 3 4 7 P L N L G S R D N D P V 5 6 S Y M B 11 12 8 9 M N D V S C L S U X C N C H L F L F X C 10 X R L V D R N C N G Chapter 19 Workbook Copyright by Pearson ducation, nc., or its affiliates. ll Rights Reserved. 310
MURDR N H PRMN Geologists are still working on solving the 250-million-year-old Permian murder mystery. o accomplish this, they piece together clues from the past that are preserved in rocks. Learning he Story s in the Rocks n the Chapter Mystery, geologists and other scientists examine rocks to help them uncover the story behind a catastrophic destruction of species and ecosystems. Rocks are extremely useful in revealing what happened on arth long ago. he type of rock in a rock layer indicates how the rock formed. Rocks are made up of minerals. he minerals in rocks tell a story. For example, igneous rocks with small mineral crystals are formed during a volcanic eruption because the lava cooled too quickly for large crystals to form. n contrast, igneous rock with large crystals formed underground. Some types of mineral crystals can only form in open spaces, such as a cave, while other crystals can only be deposited in an aquatic environment. When looking for clues about the past, geologists also look at the shape and size of a rock layer. n unconformity, or a disturbed sequence of rock layers, gives information about events that happened after a rock layer formed. For example, an earthquake can cause a rock layer to snap in two. nd slanted rock layers may indicate that uplift occurred in the area. Most of what we know about arth s ancient past comes from arth s rocks. hus, as the interpretive sign below from Yellowstone National Park shows, discussions of arth s history are typically based on geological information. From Yellowstone National Park BURD LV xcelsior Geyser s rugged crater was created by rare massive geyser eruptions. Surprisingly, it also preserves a record of early life. For thousands of years, microbes have grown in the runoff channels extending from nearby Grand Prismatic Spring. hese vast communities were buried alive as the flowing hot water deposited a crust of silica minerals. he resulting deposit, called sinter, preserves the shape of the microbial mat it entombed. s new mats grew, more layers developed. oday s formation is the result of this interplay between its living and nonliving components. Yellowstone s hydrothermal features provide a glimpse into the distant past, when intense volcanism was widespread on the young arth. he life forms found here help scientists understand the types of life that likely arose and diversified billions of years ago on our planet. Continued on next page Chapter 19 Workbook Copyright by Pearson ducation, nc., or its affiliates. ll Rights Reserved. 311
hemes Science Literacy 1. What is an unconformity? n unconformity is a disturbed sequence of rock layers. 2. Using the information on the sign, infer how the crusts of silica minerals at xcelsior Geyser formed. SMPL NSWR: Silica in the rock around the underground source of the geyser s water became dissolved in the water. he geyser spewed the water on the surface. s the water cooled and evaporated, the dissolved silica precipitated out of the water and formed a layer of silica. 3. Why do the rocks around xcelsior Geyser give scientists information about the history of life on arth? ver time, many mats of microbial life were buried alive by deposited minerals. hey then became fossilized. his created a record of the microbial life that has existed at the geyser over a long period of time. 4. Suppose a massive volcanic eruption occurred millions of years ago near xcelsior Geyser. What sort of evidence of this eruption would you expect to find? SMPL NSWR: a thick layer of ash and igneous rocks that have very small crystals between the layers of microbial mats and silica crusts 5. fter studying these signs, what else would you have liked to learn about xcelsior Geyser and Grand Prismatic Springs? SMPL NSWR: would like to have learned more about where the water in the geyser and springs comes from, how long the geyser has been erupting, and what type of microbes are found in the runoff channels. Geology of Your Region he skills used in this activity include information and media literacy, communication skills, critical thinking and systems thinking, creativity and intellectual curiosity, interpersonal and collaborative skills, and accountability and adaptability. Working in small groups, research the geological history of your town or region. Choose one geological site that particularly interests you and research it. Your research should include geological information found in the library, on the nternet, and from other sources. List the geological conditions at the site and note any interesting or unique features it has and how they formed. Design a sign that would educate visitors to the site about its geology. nclude text, photographs, and a map on your sign. valuate students signs based on the uniqueness of the site chosen, the thoroughness and correctness with which its geology is described, and the clarity and completeness of the text, pictures, and map students include in their sign. Chapter 19 Workbook Copyright by Pearson ducation, nc., or its affiliates. ll Rights Reserved. 312