1 / 66

Splash

Splash. Chapter Menu. Chapter Introduction The Origin of Earth 17.1 The Big Bang 17.2 Early Earth Evolution of Life on Earth 17.3 The Beginnings of Life 17.4 Chemical Evolution 17.5 Biological Evolution The Record of the Rocks 17.6 Microfossils and Prokaryotes 17.7 Eukaryotes

roden
Download Presentation

Splash

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Splash

  2. Chapter Menu Chapter Introduction The Origin of Earth 17.1 The Big Bang 17.2 Early Earth Evolution of Life on Earth 17.3 The Beginnings of Life 17.4 Chemical Evolution 17.5 Biological Evolution The Record of the Rocks 17.6 Microfossils and Prokaryotes 17.7 Eukaryotes Chapter Highlights Chapter Animations Contents

  3. Learning Outcomes By the end of this chapter you will be able to: A Describe the origin of the universe and probable conditions on early Earth. BEvaluate hypotheses about the origin of life and identify the probable characteristics of early life-forms. C Distinguish between chemical and biological evolution. D Describe the fossil record for prokaryotes and for eukaryotes. Learning Outcomes

  4. This photo shows stromatolite structures formed by cyanobacteria, in Shark Bay, Australia. The Origin of Life • What is required for life to begin? • How did life arise on Earth? Chapter Introduction 1

  5. This photo shows stromatolite structures formed by cyanobacteria, in Shark Bay, Australia. The Origin of Life • Of all the questions scientists investigate, the origin of life on Earth probably evokes the most public curiosity and controversy. • Where did life come from? • When did it begin? • How did the first living things look? Chapter Introduction 2

  6. End of the Introduction

  7. The Origin of Earth 17.1 The Big Bang • Measurements of light coming from deep space indicate that the stars and galaxies are rapidly moving away from each other. In the 1920s, Edwin Hubble studied light from distant galaxies to test the idea that the size of the universe is stable. 17.1 The Big Bang 1

  8. The Origin of Earth 17.1 The Big Bang (cont.) • The length of any wave (including light) changes if the object that is producing it moves toward or away from the object receiving the wave. • When a source of light moves away from the observer, the wavelength of the light increases and the visible light is a bit redder—a redshift. • When the source of light moves toward the observer, the wavelength of the wave decreases, and the visible light is a bit bluer—a blueshift. 17.1 The Big Bang 2

  9. Photographed by the Hubble Telescope, the spiral galaxy NGC 4414 is 60 million light-years away. Measurements of light from such distant galaxies provide evidence that the universe is expanding. The Origin of Earth 17.1 The Big Bang (cont.) • Hubble developed his theory of the expanding universe after measuring red shifts in the light from distant galaxies. 17.1 The Big Bang 3

  10. The Origin of Earth 17.1 The Big Bang (cont.) • Evidence indicates that, about 15 billion years ago, the whole universe was concentrated in one superdense mass that exploded. That explosion, called the big bang, hurled matter and energy into space. Gravity pulled some of the matter together to form galaxies, stars, and planets. Clumps of matter around our own star, the Sun, became planets. 17.1 The Big Bang 4

  11. The Origin of Earth 17.1 The Big Bang (cont.) • The best current estimate, based on the analysis of rocks and meteorites, is that Earth formed about 4.6 billion years ago. The Moon may have formed when a meteor collided with Earth, sending a large chunk of Earth into space. Meteors are thought to be bits of material left over from the formation of our solar system. 17.1 The Big Bang 5

  12. Geologists have worked out a history of Earth from evidence in its rocks. This timeline relates several major biological events to the history of Earth. 17.1 The Big Bang 6

  13. The Origin of Earth 17.1 The Big Bang (cont.) The history of Earth—and life—compressed into the distance between the tip of a person’s nose and the tip of the fingernail on the index finger. The history of our species, Homo sapiens, would disappear with one pass of a nail file. 17.1 The Big Bang 7

  14. The Origin of Earth 17.2 Early Earth • The decay of radioactive elements such as uranium (U), thorium (Th), and some isotopes of potassium-40 is the primary source of heat energy within Earth. The entire planet was probably hot when it first formed, and as the outer crust cooled, gases escaping from the planet’s hot interior formed a primitive atmosphere. 17.2 Early Earth 1

  15. The Origin of Earth 17.2 Early Earth (cont.) • The early atmosphere likely originated from volcanic gases: mostly nitrogen (N2), carbon dioxide, water vapor, and hydrogen (H2), with small amounts of carbon monoxide (CO). All geologic evidence indicates that oxygen gas (O2) probably was not present in the early atmosphere. 17.2 Early Earth 2

  16. The Origin of Earth 17.2 Early Earth (cont.) • Oxygen began to accumulate in the atmosphere after the first photosynthetic organisms started to produce it about 2.1–2.4 billion years ago. Modern levels of oxygen in the atmosphere were probably reached about 360 million years ago as plants became abundant on land. 17.2 Early Earth 3

  17. End of Section 1

  18. Evolution of Life on Earth 17.3 The Beginnings of Life • The surface of Earth 4.6 billion years ago would have been hostile to modern life. • Organic compounds do not form easily in an atmosphere rich in nitrogen and carbon dioxide. • Ultraviolet radiation from the Sun bathed the surface of Earth. • There were extreme temperature variations. • The was a scarce supply of oxygen gas. 17.3 The Beginnings of Life 1

  19. Earth’s atmosphere Click the image to view an animated version. 17.3 The Beginnings of Life 2

  20. Evolution of Life on Earth 17.3 The Beginnings of Life (cont.) • Popular scientific explanations for the beginning of life include the following: 1. Life originated on some planet of another star and traveled to Earth through space. 2. Life originated by unknown means on Earth. 3. Life evolved from nonliving substances through interaction with the environment. 17.3 The Beginnings of Life 3

  21. Evolution of Life on Earth 17.3 The Beginnings of Life (cont.) • Many people believe that a supernatural force or deity created life. That explanation is not within the scope of science, therefore, such beliefs are not part of scientific debates about the origin of life. 17.3 The Beginnings of Life 4

  22. Evolution of Life on Earth 17.4 Chemical Evolution • Most research on the origin of life focuses on the idea that life evolved from nonliving substances by interacting with the natural environment. In the 1920s, the Soviet scientist Alexander Oparin and the British scientist J. B. S. Haldane separately described this hypothesis in detail. 17.4 Chemical Evolution 1

  23. Evolution of Life on Earth 17.4 Chemical Evolution (cont.) • Oparin and Haldane proposed: • The early atmosphere consisted of methane, ammonia, hydrogen, and water vapor. • Energy sources such as radioactivity, lightning, cosmic radiation from space, and heat energy from volcanoes caused gases in the atmosphere to react, forming organic compounds. • Those compounds then accumulated in the soup-like hot oceans. 17.4 Chemical Evolution 2

  24. Evolution of Life on Earth 17.4 Chemical Evolution (cont.) • They hypothesized that life evolved by further chemical reactions and transformations in the complex organic soup. • Both thought the first life-forms were heterotrophs that fed on the organic compounds in the soup. • These ideas are the basis of the heterotroph hypothesis for the origin of life. 17.4 Chemical Evolution 3

  25. Evolution of Life on Earth 17.4 Chemical Evolution (cont.) • The Oparin-Haldane version of the heterotroph hypothesis requires three major steps for the origin of life: 1. There had to be a supply of organic molecules, produced by nonbiological processes. 2. Some processes had to assemble those small molecules into polymers such as nucleic acids and proteins. 3. Other processes had to organize the polymers into a system that could replicate itself, using the organic molecules produced in step 1. 17.4 Chemical Evolution 4

  26. Evolution of Life on Earth 17.4 Chemical Evolution (cont.) • In the 1950s, Harold Urey and Stanley Miller worked on the problem of how organic compounds could form in an inorganic environment. They were able to create organic compounds and amino acids in an airtight apparatus under conditions that might have existed on Earth 4.6 billion years ago. 17.4 Chemical Evolution 5

  27. A drawing of Miller’s apparatus Click the image to view an animated version. 17.4 Chemical Evolution 6

  28. Evolution of Life on Earth 17.4 Chemical Evolution (cont.) • More recent experiments have produced at least 13 of the 20 common amino acids found in proteins. Those experiments also have produced all the bases found in DNA and RNA and even small amounts of ribose, the sugar in RNA. 17.4 Chemical Evolution 7

  29. Evolution of Life on Earth 17.4 Chemical Evolution (cont.) • Evidence from meteorites indicates that organic compounds also form in space. (a), Cyril Ponnamperuma and his associates were the first to detect amino acids in a meteorite when they analyzed a sample of the Murchison meteorite (b). Instruments flown through the comet’s tail of Comet Halley detected organic compounds. 17.4 Chemical Evolution 8

  30. Evolution of Life on Earth 17.4 Chemical Evolution (cont.) • Some organic molecules also may have formed at volcanic vents deep in the ocean. Regardless of origin, there is a plausible explanation for step 1 of the Oparin-Haldane hypothesis. 17.4 Chemical Evolution 9

  31. Repeating crystal structures in clay particles (scanning electron micrograph) may have served as a blueprint for assembling the first biochemical polymers. Evolution of Life on Earth 17.4 Chemical Evolution (cont.) • For the formation of complex molecules to occur, smaller molecules must been concentrated enough to make them collide and react with each other. In 1985, A. G. Cairns-Smith suggested that clay particles might have helped to form the first organic polymers by catalyzing the bonding together of these small molecules to form proteins and other polymers. 17.4 Chemical Evolution 10

  32. Evolution of Life on Earth 17.4 Chemical Evolution (cont.) • The work by Cairns-Smith and others since allows us to infer that polymers could have formed from simple organic compounds in the prebiological soup. Self-replication, a central feature of living systems, is the third and final step for the origin of life. Research into self-replication has led to the hypothesis that life began in an “RNA world.” 17.4 Chemical Evolution 11

  33. Evolution of Life on Earth 17.4 Chemical Evolution (cont.) • According to the RNA-world hypothesis: • RNA served as both information molecule and catalyst at first. • DNA later became the main information molecule and protein enzymes the primary biological catalysts. So far, scientists have found no RNA that can replicate itself completely. 17.4 Chemical Evolution 12

  34. Evolution of Life on Earth 17.4 Chemical Evolution (cont.) • RNA molecules can undergo simulated Darwinian evolution in the laboratory. Beginning with a mixture of RNA molecules with various sequences, directed evolution allows a scientist to develop a ribozyme (RNA enzyme) that can catalyze its own replication or another desired reaction. 17.4 Chemical Evolution 13

  35. Evolution of Life on Earth 17.5 Biological Evolution • The boundary between chemical evolution and biological evolution may be the formation of self-replicating polymers. Life could be described as “a self-sustained chemical system that is capable of undergoing Darwinian, or biological, evolution.” 17.5 Biological Evolution 1

  36. Evolution of Life on Earth 17.5 Biological Evolution (cont.) • Biological evolution consists of three processes: 1. self-reproduction 2. mutation that can be inherited 3. natural selection 17.5 Biological Evolution 2

  37. Evolution of Life on Earth 17.5 Biological Evolution (cont.) • Cell theory holds that all life is made of cells and that all cells come from preexisting cells. The origin of cells and membranes is still not clearly understood. In the early 1980s, Carl Woese suggested that life began on Earth before the planet was fully formed as water droplets that functioned as primitive cells. 17.5 Biological Evolution 3

  38. Evolution of Life on Earth 17.5 Biological Evolution (cont.) • Other possibilities for the first life-forms include proteins, DNA, and RNA. Amino acids in the oceans may have joined spontaneously to form proteins. Many proteins are enzymes that catalyze the synthesis of other substances, but there is no known way for proteins to replicate themselves without the help of RNA. 17.5 Biological Evolution 4

  39. Evolution of Life on Earth 17.5 Biological Evolution (cont.) • Short strands of RNA can self-replicate. RNA also stores information, directs the synthesis of proteins, and has limited ability as a catalyst. In certain viruses, such as the virus that causes AIDS, RNA also directs the synthesis of DNA. 17.5 Biological Evolution 5

  40. Evolution of Life on Earth 17.5 Biological Evolution (cont.) • A few scientists maintain that the first life-forms could have functioned only if they contained both proteins and nucleic acids. Viruses consist of DNA or RNA surrounded by a protein coat. Viruses are so dependent on their host cells that they probably originated after their hosts and their role in evolution is unclear. 17.5 Biological Evolution 6

  41. Evolution of Life on Earth 17.5 Biological Evolution (cont.) • All the ideas about the origin of life and the nature of the first life-forms have supporters and opponents. 17.5 Biological Evolution 7

  42. End of Section 2

  43. The Record of the Rocks 17.6 Microfossils and Prokaryotes • Some scientists have tried to investigate early life-forms by searching for fossils. What may be the oldest known microfossils, or fossil microorganisms, were discovered in 1993 in northwestern Australia. 17.6 Microfossils and Prokaryotes 1

  44. A 3.5-billion-year-old prokaryote fossil in a stromatolite from western Australia. This fossil contains the oldest known cells. The Record of the Rocks 17.6 Microfossils and Prokaryotes (cont.) • The fossils are of tiny, single-celled filaments that resemble certain modern bacteria capable of photosynthesis. 17.6 Microfossils and Prokaryotes 2

  45. The Record of the Rocks 17.6 Microfossils and Prokaryotes (cont.) • The microscopic fossils were embedded in mineral grains encased in a type of rock that formed almost 3.5 billion years ago. This discovery showed that life appeared on Earth much earlier than previously thought. 17.6 Microfossils and Prokaryotes 3

  46. The Record of the Rocks 17.6 Microfossils and Prokaryotes (cont.) • The Australian fossils were found with domelike structures called stromatolites that are composed of many wafer-thin layers of rock. Today, limestone-secreting bacteria form similar structures at Shark Bay, Australia. 17.6 Microfossils and Prokaryotes 4

  47. The Record of the Rocks 17.6 Microfossils and Prokaryotes (cont.) (a), Approximately 530 million-year-old fossil stromatolites from Wyoming. Note the characteristic layered structure. The image is approximately 5 cm across. (b), Modern living stromatolites in Shark Bay, Australia, built by cyanobacteria. Each dome is about 30–100 cm in diameter. 17.6 Microfossils and Prokaryotes 5

  48. The Record of the Rocks 17.6 Microfossils and Prokaryotes (cont.) • Older microfossils will be very difficult to find as they have melted, eroded, or otherwise changed until they are no longer recognizable. These fossils are thought to be prokaryotes, but their structures were probably less organized than modern prokaryotes. 17.6 Microfossils and Prokaryotes 6

  49. The Record of the Rocks 17.6 Microfossils and Prokaryotes (cont.) • Carl Woese suggests that the first organisms may have been methanogens—anaerobic bacteria that obtain energy by using carbon dioxide to oxidize hydrogen. Methanogens and related bacteria live today in conditions thought to be like those of early Earth such as near hydrothermal volcanic vents on the seafloor. 17.6 Microfossils and Prokaryotes 7

  50. The Record of the Rocks 17.7 Eukaryotes • The first microfossils that may have been eukaryotes are about 2.1 billion years old. Fossil evidence indicates that eukaryotic cells became common by 750 million years ago. Eukaryotic cells contain membrane-enclosed organelles such as a nucleus, mitochondria, and chloroplasts. 17.7 Eukaryotes 1

More Related