Transcript Objectives
Chapter 12 History of Life on Earth Section 1: How Did Life Begin? Section 2: The Evolution of Cellular Life Section 3: Life Invaded the Land Section 1 History of Life on Earth Objectives: •Summarize how radioisotopes can be used in determining Earth's age. •Compare two models that describe how the chemicals of life originated. •Describe how cellular organization might have begun. •Recognize the importance that a mechanism for heredity has to the development of life. Section 1 How Did Life Begin? The Age of Earth •Measuring Earth’s Age The Earth formed about 4.5 billion years ago according to evidence obtained by radiometric dating. Section 1 How Did Life Begin? Formation of the Basic Chemicals of Life •The “Primordial Soup” Model Miller and Urey’s “primordial soup” model proposes that important organic molecules arose in the early earth’s oceans due to chemical reactions of atmospheric gases and water activated by heat sources. •Reevaluating the Miller-Urey Model The mixture of gases used in Miller’s “primordial soup” experiments could not have existed on early earth. •The Bubble Model Lerman suggest that the key processes that formed the chemical needed for life took place in bubbles on the ocean’s surface. Section 1 How Did Life Begin? Precursors of the First Cells •A Possible Role as Catalysts Scientists think that selfreplicating RNA “enzyme-like” molecules formed before DNA or proteins formed. •Microspheres and Coacervates Scientists think that the first cells may have developed from microspheres (amino acid and lipid droplets) or coacervate drops (amino acid, lipid, and sugar droplets). •Origin of Heredity The development of heredity made it possible for organisms to pass traits to subsequent generations. The first genetic material may have been RNA “enzymes” that catalyzed the earliest proteins. Section 2 The Evolution of Cellular Life Objectives: •Distinguish between the two groups of prokaryotes. •Describe the evolution of eukaryotes. •Recognize an evolutionary advance first seen in protists. •Summarize how mass extinctions have affected the evolution of life on Earth. Section 2 The Evolution of Cellular Life The Evolution of Prokaryotes •Two Groups of Prokaryotes Prokaryotes are the oldest organisms and are divided into two groups, archaebacteria and eubacteria. Section 2 The Evolution of Cellular Life The Evolution of Eukaryotes •Endosymbiosis Prokaryotes likely gave rise to eukaryotes through the process of endosymbiosis in which larger prokaryotic cells incorporate smaller prokaryotic cells. •The Origins of Mitochondria and Chloroplasts The theory of endosymbiosis proposes that mitochondria are the descendants of symbiotic, aerobic eubacteria and chloroplasts are the descendants of symbiotic, photosynthetic eubacteria. Section 2 The Evolution of Cellular Life Multicellularity •Evolution of Multicellular Organisms Multicellularity arose many times and resulted in many different groups of multicellular organisms. Protists include the first multicellular organisms. •Origins of Modern Organisms All of the major animal phyla probably originated during the Cambrian period. Section 2 The Evolution of Cellular Life Mass Extinctions •Mass Extinctions Extinctions influenced the evolution of the species extant today. At least five major or mass extinctions have occurred on Earth. Section 3 Life Invaded the Land Objectives: •Relate the development of ozone to the adaptation of life to the land. •Identify the first multicellular organisms to live on land. •Name the first animals to live on land. •List the first vertebrates to leave the oceans. Section 3 Life Invaded the Land The Ozone Layer •Formation of the Ozone Layer Ancient cyanobacteria produced oxygen, some of which became ozone. •Importance of Ozone Ozone, which blocks UV radiation from the sun, enabled organisms to live on land. Section 3 Life Invaded the Land Plants and Fungi on Land •Mycorrhizae Plants and fungi formed mycorrhizae, symbiotic associations of plants and fungi. Mycorrhizae were the first multicellular organisms to live on land. Section 3 Life Invaded the Land Arthropods •Arthropods Arthropods are animals with hard outer skeletons. •Flight in Arthropods Insects evolved flight and were the first animals to leave the ocean. Section 3 Life Invaded the Land Vertebrates •Fishes The first vertebrates were small, jawless fish that evolved in the oceans. •Amphibians The first invertebrates to invade dry land were amphibians. •Reptiles Reptiles are better suited to dry land than amphibians. Section 3 Life Invaded the Land Vertebrates continued •Mammals and Birds The extinction of many reptile species enabled birds and mammals to become the dominant vertebrates on land. •Continental Drift The movement of the continents on the surface of the Earth has contributed to the geographic distribution of some species.