Name Class Date 19.3 Earth s Early History Lesson Objectives Identify some of the hypotheses about early Earth and the origin of life. Explain the endosymbiotic theory. Explain the significance of sexual reproduction in evolution. Lesson Summary The Mysteries of Life s Origins Earth s early atmosphere contained toxic gases. The atmosphere also contained little or no oxygen. In the 1950s, Stanley Miller and Harold Urey set out to determine if organic molecules could assemble under early Earth conditions. They filled a container with water and gases that they thought represented the composition of Earth s early atmosphere. They passed electric sparks through the mixture to simulate lightning. Soon, organic compounds formed. The 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. RNA and DNA also could have evolved from simple organic molecules. The first known life forms evolved about 3.5 billion years ago. They were single celled and looked like modern bacteria. Eventually, photosynthetic bacteria became common. During photosynthesis, the bacteria produced oxygen. The oxygen accumulated in the atmosphere. The rise of oxygen drove some life forms to extinction. At the same time, other life forms evolved that depended on oxygen. Origin of Eukaryotic Cells The first eukaryotes, or organisms with nuclei, evolved from prokaryotes that began to develop internal cell membranes. One explanation for how eukaryotes evolved is the endosymbiotic theory. This 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.
BUILD Vocabulary A. The chart below shows the key term in this lesson with its definition. Completee the chart by writing a LATIN / GREEK strategy to help you remember the meaning of the term. Word Latin & Greek strategy Endosymbiosis BUILD Understanding Flowchart A flowchart is a way to show a sequence of events. You can make a flowchart by writing the steps in a series of connected boxes. As you read Lesson 3, complete the flowchart to show the major steps from the origin of Earth to the evolution of eukaryotic cells. Earth forms. Organic molecules form. RNA and DNA evolve.
The Mysteries of Life s Origins Scientists have as many questions as answers about the origins of life on Earth. The study of life s origins is a branch of scientific research that is always changing. Scientists do know that early Earth was a very different place than today s Earth. Follow the directions. 1. Fill in the chart with information about early Earth and today s Earth. Use terms from the box. brown oceans blue skies pinkish-orange skies blue oceans no life many different life forms about 20% oxygen little to no oxygen Early Earth Today s Earth Oceans Skies Atmosphere Life Each of the following statements is false. Rewrite the statements to make them true. 2. Oceans on early Earth were blue because they contained lots of dissolved iron. 3. The atmosphere on early Earth could support human life because there was no oxygen. 4. For millions of years, asteroids shook Earth s crust. 5. Microspheres evolved from living cells. 6. The first cells on Earth were eukaryotic.
The Mysteries of Life s Origins Production of Free Oxygen Early Earth s atmosphere was mostly a mixture of carbon dioxide, water vapor, and nitrogen. There was little to no oxygen. Life as we know it today developed because of the production of free oxygen. A cause-and-effect chart is similar to a flowchart. It shows what the impact of a certain event is. The event is the cause. The impact of the event is the effect. Many causes can also be effects. Follow the directions. 7. Complete the cause-and-effect chart below. Use the sentences in the box. Organisms that used oxygen for respiration evolved. The first cells became extinct. The oceans changed color from brown to blue. The ozone layer formed and skies turned blue. The iron oxide sank to the ocean floor. Cause: Photosynthetic bacteria began producing oxygen. Cause/Effect: Oxygen combined with iron in the oceans to form iron oxide. Cause/Effect: Oxygen accumulated in the atmoshpere. Cause/Effect: Cause/Effect: Effect: Cause/Effect: Effect: Answer the questions using complete sentences. 8. What life process put oxygen into the atmosphere? 9. Why do you think the first cells became extinct?
Origin of Eukaryotic Cells Endosymbiotic Theory The endosymbiotic theory explains the evolution of eukaryotic cells. According to the theory, ancient prokaryotes developed a symbiotic relationship with smaller prokaryotes that lived inside them. Some of these smaller prokaryotes could use oxygen to make ATP. These aerobic prokaryotes evolved into mitochondria. Others could perform photosynthesis. These evolved into chloroplasts. The diagram below shows the stages in the endosymbiotic theory. Follow the directions to finish the diagram. 10. Draw the final step in the endosymbiotic theory. Your drawing should show a primitive eukaryotic cell that performed photosynthesis. 11. Label the chloroplast in your drawing. Ancient Aerobic Prokaryote Ancient Anaerobic Prokaryote Nuclear envelope evolving Primitive Aerobic Eukaryote Mitochondrion Ancient Photosynthetic Prokaryote Animals, fungi, and non-plantlike protists Plants and plantlike protists Primitive Photosynthetic Eukaryote Answer the questions. 12. Animals evolved from primitive eukaryotic cells with which structure? chloroplast mitochondria nucleus 13. What evidence shows that bacteria and organelles of living cells share a common ancestry?
Use the diagram of the Miller-Urey experiment to answer Questions 14-16. 14. THINK VISUALLY Label the diagram to show which part of Miller and Urey s apparatus simulated lightning storms on early Earth. 15. What was the purpose of Miller and Urey s experiment? 16. Explain the results of the Miller-Urey experiment. What did these findings suggest? Origin of Eukaryotic Cells 17. Explain the endosymbiotic theory IN YOUR OWN WORDS!
Sexual Reproduction and Multicellularity 18. How did sexual reproduction speed up the evolutionary process? 19. What is the most likely cause of the great amount of diversity currently seen in multicellular life forms? Apply the Big idea 20. Once DNA evolved, what could have caused it to become the primary means of transmitting genetic information instead of RNA? (Hint: think about the structure of DNA & RNA)