Outline 17-2: Earth's Early History Photo credit: Jackie Beckett/American Museum of Natural History Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall I. Early Earth The Earth is thought to be 4.5 - 5 billion years old. At first a fiery ball of molten rock Eventually cooled & formed a rocky crust Water vapor condensed to form oceans Scientists think that first life evolved in these oceans Copyright Pearson Prentice Hall

II. Origins of Living Cells Biogenesis does not answer the question: How did life begin on Earth? No one will ever know for certain how life began Scientists have developed theories about the origin of life from testing scientific hypotheses about conditions on early Earth Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall How basic chemicals could form All elements necessary for life were apparently found on Earth from its beginnings. Physical & chemical processes alone can explain the origins of ever more complex organic chemicals on our planet This hypothesis has been tested & confirmed many times in laboratory experiments. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 2. Primordial soup model Oparin & Haldane’s (1920s) idea: Earth’s early atmosphere contained ammonia, hydrogen, methane & water vapor Heat from volcanoes, sunlight and lightning could have caused them to form organic compounds Accumulated in a sea called the primordial soup Copyright Pearson Prentice Hall

3. Miller & Urey’s Experiment (1953) Copyright Pearson Prentice Hall

The First Organic Molecules - Miller and Urey’s Experiment Mixture of gases simulating atmosphere of early Earth Spark simulating lightning storms Condensation chamber Water vapor Cold water cools chamber, causing droplets to form. Miller and Urey produced amino acids, which are needed to make proteins, by passing sparks through a mixture of hydrogen, methane, ammonia, and water. This and other experiments suggested how simple compounds found on the early Earth could have combined to form the organic compounds needed for life. Liquid containing amino acids and other organic compounds Copyright Pearson Prentice Hall

4. Reevaluating primordial soup model Early atmosphere probably did NOT contain methane & ammonia. It probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water. Without methane & ammonia some key biological molecules are not made. So how could organic molecules form? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 5. Bubble model Louis Lerman (1986) suggested key processes took place within bubbles on the ocean’s surface. While inside bubbles, gases get protection from UV radiation Reactions could take place faster inside bubbles (concentrated) Bubbles could later rise to surface & release organic molecules into ocean Energy could cause these to react & build even more complex molecules Copyright Pearson Prentice Hall

C. How complex chemicals could form Amino acids could have then spontaneously linked together to form proteins RNA has been found to form spontaneously in water RNA could have been first self- replicating molecule It could also have catalyzed the first assembly line of proteins Copyright Pearson Prentice Hall

The Puzzle of Life's Origin Proteins build cell structures and catalyze chemical reactions RNA and the Origin of Life RNA nucleotides Simple organic molecules RNA helps in protein synthesis Abiotic “stew” of inorganic matter One hypothesis about the origin of life, illustrated here, suggests that RNA could have evolved before DNA. Scientists have not yet demonstrated the later stages of this process in a laboratory setting.  RNA able to replicate itself, synthesize proteins, and function in information storage DNA functions in information storage and retrieval Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 3. Microspheres Cells Lipids have been shown to gather in water & form a bilayer sphere Chains of amino acids will gather into tiny vesicles called proteinoid microspheres Have selectively permeable membranes & can store & release energy These vesicles could have been first step toward cells Problem: They don’t reproduce! Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall III. Oldest Fossils Are microfossils of unicellular prokaryotic organisms resembling modern bacteria Found in rocks 3.5 billion years old. Were anaerobic organisms. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall IV. First Oxygen About 2.2 billion years ago, photosynthetic bacteria began to pump oxygen into the oceans. Next, oxygen gas accumulated in the atmosphere. Rise of oxygen probably caused some life forms to go extinct while others took advantage of oxygen in new ways (aerobic respiration) Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall V. The Endosymbiotic Theory Idea that eukaryotic cells formed from a symbiosis among several different prokaryotes. Ones that used oxygen evolved into mitochondria Ones that could do photosynthesis evolved into chloroplasts Copyright Pearson Prentice Hall

Origin of Eukaryotic Cells DON’T COPY! Endosymbiotic Theory Ancient Prokaryotes Chloroplast Plants and plantlike protists Aerobic bacteria Photosynthetic bacteria Nuclear envelope evolving Mitochondrion Primitive Photosynthetic Eukaryote The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles. Animals, fungi, and non-plantlike protists Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote Copyright Pearson Prentice Hall

Origin of Eukaryotic Cells Aerobic bacteria Ancient Prokaryotes Nuclear envelope evolving The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles. Ancient Anaerobic Prokaryote Copyright Pearson Prentice Hall

Origin of Eukaryotic Cells Mitochondrion Prokaryotes that use oxygen to generate energy- rich molecules of ATP evolved into mitochondria. The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles. Primitive Aerobic Eukaryote Copyright Pearson Prentice Hall

Origin of Eukaryotic Cells DON’T COPY! Prokaryotes that carried out photosynthesis evolved into chloroplasts. Chloroplast Photosynthetic bacteria The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles. Primitive Photosynthetic Eukaryote Copyright Pearson Prentice Hall

Outline 17-3: Evolution of Life on Earth 11/30/2018

Prokaryotes A. Oldest fossil dated at 3. 5 bya Prokaryotes A. Oldest fossil dated at 3.5 bya (billions of years ago) B. These were anaerobic prokaryotes C. Later, 2.2 bya, came cyanobacteria, photosynthetic bacteria. 1. They produced the first oxygen for the planet. a. Today 21% of atmosphere is oxygen D. Two types of prokaryotes: 1. Archaebacteria 2. Eubacteria

II. First Eukaryotes formed A. Oldest eukaryote fossils dated at. 1 II. First Eukaryotes formed A. Oldest eukaryote fossils dated at 1.5 bya B. These have a nucleus & internal membranes C. Probably occurred partially by the process of endosymbiosis

Multicellularity Evolved A. 6 kingdoms, or groups, of life: 1 Multicellularity Evolved A. 6 kingdoms, or groups, of life: 1. Eubacteria 2. Archaebacteria 3. Protista 4. Fungi 5. Plantae 6. Animalia B. Half of biomass on earth is unicellular 1. Limitations: a. No specialization occurs

C. Multicellularity probably evolved. more than once 1 C. Multicellularity probably evolved more than once 1. Oldest multicellular organisms date to 700 mya. 2. Multicellular protists are red, green & brown algae (kelp=seaweed) 3. Fungi, plants & animals all evolved from different protists. 4. Most groups of organisms alive today seemed to have evolved during the Cambrian Explosion (~540-505 mya)

IV. Mass extinctions: Death of many. organisms at once. A IV. Mass extinctions: Death of many organisms at once A. Happened repeatedly during Earth’s history: 1. End of PreCambrian (540 mya) 2. End of Paleozoic (245 mya) 3. End of Mesozoic (65 mya)

Causes of mass extinctions. Meteorite impact theory Causes of mass extinctions? Meteorite impact theory for end of Mesozoic Era

V. Evolution of the Ozone Layer. A. Sun provides light as well as V. Evolution of the Ozone Layer A. Sun provides light as well as dangerous ultraviolet radiation B. What helped life leave the oceans? 1. Ozone Layer a. Cyanobacteria produced O2 b. Sun hits O2 & creates O3 (ozone) c. Ozone layer blocks UV radiation

Ozone Layer

VI. First Land Creatures. A. First creatures needed to live on VI. First Land Creatures A. First creatures needed to live on bare rock (no soil yet) B. Fungi & lichens probably started out on land first. C. Photosynthetic plants came later

VII. First Land Animals. A. By 330 mya there were extensive VII. First Land Animals A. By 330 mya there were extensive forests on land B. Provided ample food for animals C. First land animals were the arthropods 1. Characteristics: a. hard exoskeleton & jointed legs 2. Examples: a. Crustaceans (lobsters, crabs) b. Insects (most abundant animals today) c. Arachnids (spiders, scorpions)

VIII. Vertebrates. A. Animals with backbones. B VIII. Vertebrates A. Animals with backbones B. Come in five major groups (Classes): 1. Fishes a. Evolved by ~ 500 mya b. First were small jawless fishes c. Then came jawed fishes (430 mya)

2. Amphibians. a. Evolved by ~370 mya. b. First vertebrates on land. c 2. Amphibians a. Evolved by ~370 mya b. First vertebrates on land c. Smooth skinned; need to live near water d. Adaptations: Lungs, limbs evolved from fins e. Examples: Frogs, toads, salamanders

3. Reptiles. a. Evolved by ~350 mya. b. Adaptations: 3. Reptiles a. Evolved by ~350 mya b. Adaptations: Waterproof skin & waterproof eggs allowed them to live in dry climates c. Examples: Snakes, lizards, turtles, crocodiles & dinosaurs

4. Mammals. a. Evolved by ~220 mya. b 4. Mammals a. Evolved by ~220 mya b. Minor group at first; expanded after extinction of dinosaurs c. Adaptations: Hair, warm-blooded, mammary glands to feed young milk d. Examples: Rodents, primates, felids (cats), canids (dogs), etc.

5. Birds a. Evolved by ~150 mya probably from branch of the dinosaurs b. Archeaopteryx – fossil of earliest bird. Shows reptilian & bird characteristics. c. Adaptations: Warm-blooded, feathers, hard- shelled eggs d. Examples: Ostrich, kiwi, seagulls, eagles, mockingbirds, hummingbirds