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Unit 1 NOS/Evolution ppt #6 Evolution: Early Earth History Slide 1 of 36 Copyright Pearson Prentice Hall End Show Earth is about 4.6 Billion years old!! Fossil records tell the Earth’s story. Over years many many layers of rock have formed. Many fossils are found within layers of rock. Fossils are the preserved remains or traces of organisms that lived in the past Slide 2 of 36 Copyright Pearson Prentice Hall End Show 17-1 The Fossil Record Interpreting Fossil Evidence Interpreting fossil evidence to show evolution or organisms 1. Relative Dating Using the LAW of SUPERPOSITION: Rock layers form in order by age—the oldest on the bottom, with more recent layers on top. In relative dating, the age of a fossil is determined by comparing its placement to that of fossils in other layers of rock. Slide 3 of 40 Copyright Pearson Prentice Hall End Show 17-1 The Fossil Record Interpreting Fossil Evidence Relative Dating Slide 4 of 40 Copyright Pearson Prentice Hall End Show 17-1 The Fossil Record In Relative dating you are comparing 1 fossil to another, generating a history. For this you need an INDEX FOSSIL INDEX FOSSIL = An index fossil is a species that is recognizable and that existed for a short period but had a wide geographic range. Slide 5 of 40 Copyright Pearson Prentice Hall End Show 17-1 The Fossil Record Interpreting Fossil Evidence Interpreting Fossil Evidence to show evolution of organisms 2. Absolute Dating= radioactive dating Paleontologists determine the age of fossils using the fact that elements decay into measureable radioactive quantities. Scientists use radioactive decay to assign an absolute age to rocks Using radioactive decay, C12-C14scientists can determine true age of a fossil. Copyright Pearson Prentice Hall Slide 6 of 40 End Show Radioactive dating is the use of half-lives to determine the age of a sample. A half-life is the length of time required for half of the radioactive atoms in a sample to decay. 17-1 The Fossil Record Interpreting Fossil Evidence By comparing the amounts of carbon-14 and carbon-12 in a fossil, researchers can determine when the organism lived. In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains. Slide 8 of 40 Copyright Pearson Prentice Hall End Show Compare/Contrast Table Section 17-1 Comparing Relative and Absolute Dating of Fossils Can determine Is performed by Drawbacks Relative Dating Absolute Dating Age of fossil with respect to another rock or fossil (that is, older or younger) Age of a fossil in years Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen Imprecision and limitations of age data Difficulty of radioassay laboratory methods 17-1 The Fossil Record Geologic Time Scale Paleontologists use a scale called the geologic time scale to represent evolutionary time. It is time on the scale of the history of Earth, which spans 4.6 billion years Scientists first developed the geologic time scale by studying rock layers and index fossils worldwide. Slide 10 of 40 Copyright Pearson Prentice Hall End Show Geological time scale shows macroevolution marked by mass extinctions and episodic speciation. Episodic speciation is a pattern of periodic large scale increase in new species that follows mass extinctions. Compare/Contrast Table Section 17-1 Over Earth’s History, 99.9% of all species that have lived on Earth have become extinct, which means that the species has died out. Extinction means the death of an entire species. Major Extinctions Precambrian Extinction: The abrupt and nearly complete disappearance of life form in late Precambrian may have resulted from unbalanced predation, grazing, or competition, or yet another environmental crisis such as supercontinent breakup, changes in ocean chemistry, and/or rising sea levels. Whatever the causes, most species disappeared by the end of the Precambrian, about 542 million years ago. Their extinction, however, appears to have paved the way for a spectacular evolution of much more familiar life, which marks the beginning of the modern Phanerozoic Eon: the Cambrian explosion. Cambrian Explosion Cambrian explosion followed Precambrian extinction. The evidence shows that nearly all modern animal phyla, including our own chordate phylum, are represented in this diversity of life. Major Extinctions Permian Extinction: During the Permian period, all the major landmasses of earth combined into a single supercontinent, Pangaea. During the formation of the supercontinent Pangaea, most marine invertebrate species disappeared with the loss of their coastal habitats. The Permian ended with the most massive extinction of all time; 99.5% of all species disappeared, opening the door for a new radiation of species in the Mesozoic. Major Extinctions “K-T” (Cretaceous-Tertiary) Extinction: The dramatic extinction of all dinosaurs (except the lineage which led to birds) marked the end of the Cretaceous. A collision/explosion between the Earth and a comet or asteroid could have spread debris which set off tsunamis, altered the climate (including acid rain), and reduced sunlight 10-20%. A climatic shift to cooler temperatures because of diminished solar energy coincided with the extinction of dinosaurs. A consequent reduction in photosynthesis would have caused a drastic disruption in food chains. The massive extinction and sharp geologic line led geologists to define the end of the Mesozoic and the beginning of our modern Era, the Cenozoic, with this event. 17-2 Earth's Early History Formation of Earth Evolution of THE FIRST ORGANISMS… What substances made up Earth's early atmosphere? Slide 19 of 36 Copyright Pearson Prentice Hall End Show 17-2 Earth's Early History Formation of Earth Earth's early atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide, and water. Slide 20 of 36 Copyright Pearson Prentice Hall End Show 17-2 Earth's Early History The Puzzle of Life's Origin The Puzzle of Life's Origin Evidence suggests that 200–300 million years after Earth had liquid water, cells similar to modern bacteria were common. Slide 21 of 36 Copyright Pearson Prentice Hall End Show 17-2 Earth's Early History The Puzzle of Life's Origin Formation of Protocells In certain conditions, large organic molecules like RNA form tiny bubbles called protocells. Protocells are not cells, but they have selectively permeable membranes and can store and release energy. Slide 22 of 36 Copyright Pearson Prentice Hall End Show 17-2 Earth's Early History The Puzzle of Life's Origin Hypotheses suggest that structures similar to protocells might have acquired more characteristics of living cells. Slide 23 of 36 Copyright Pearson Prentice Hall End Show 17-2 Earth's Early History The Puzzle of Life's Origin Evolution of RNA and DNA How could DNA and RNA have evolved? Several hypotheses suggest: • Some RNA sequences can help DNA replicate under the right conditions. • Some RNA molecules can even grow and duplicate themselves suggesting RNA might have existed before DNA. Slide 24 of 36 Copyright Pearson Prentice Hall End Show 17-2 Earth's Early History Free Oxygen About 2.2 billion years ago, photosynthetic bacteria began to pump oxygen into the oceans. Next, oxygen gas accumulated in the atmosphere. Slide 25 of 36 Copyright Pearson Prentice Hall End Show 17-2 Earth's Early History Free Oxygen The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration. Slide 26 of 36 Copyright Pearson Prentice Hall End Show 17-2 Earth's Early History Origin of Eukaryotic Cells The Endosymbiotic Theory The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Prokaryotes became the organelles within the Eukaryotic cell. Slide 27 of 36 Copyright Pearson Prentice Hall End Show 17-2 Earth's Early History Origin of Eukaryotic Cells Endosymbiotic Theory Ancient Prokaryotes Chloroplast Aerobic bacteria Nuclear envelope evolving Ancient Anaerobic Prokaryote Photosynthetic bacteria Plants and plantlike protists Mitochondrion Primitive Aerobic Eukaryote Primitive Photosynthetic Eukaryote Animals, fungi, and non-plantlike protists Slide 28 of 36 Copyright Pearson Prentice Hall End Show 17-2 Earth's Early History Origin of Eukaryotic Cells About 2 billion years ago, prokaryotic cells began evolving internal cell membranes. The result was the ancestor of all eukaryotic cells. According to the endosymbiotic theory, eukaryotic cells formed from a symbiosis among several different prokaryotes. Eukaryotic, multicellular life evolved with sexual reproduction which increases genetic variability. Thus…evolution of higher life forms! Slide 29 of 36 Copyright Pearson Prentice Hall End Show Concept Map Section 17-2 Evolution of first life Early Earth was hot; atmosphere contained poisonous gases. Earth cooled and oceans condensed. Simple organic molecules may have formed in the oceans.. Small sequences of RNA may have formed and replicated. First prokaryotes formed when RNA or DNA was enclosed in microspheres. Later prokaryotes were photosynthetic and produced oxygen. An oxygenated atmosphere capped by the ozone layer protected Earth. First eukaryotes may have been communities of prokaryotes. Multicellular eukaryotes evolved. Sexual reproduction increased genetic variability, hastening evolution.