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History of Life on Earth Biology Chapter 12 Ms. Pollock Spring 2008 How Did Life Begin? Earth believed 4.5 billion years old Began as fiery ball of molten rock Cooled and formed rocky crust Water vapor in atmosphere condensed to form oceans, where first life believed to have developed Timeline of development created using radiometric dating How Did Life Begin? Life thought to have begun as the result of interactions between nonliving matter First billion years of Earth’s existence Simple organic molecules created and energized by the sun and volcanic heat Molecules combined to create new, more complex molecules Primordial Soup 1920s model suggested by Russian A.I. Oparin and British scientist J.B.S. Haldane Early oceans containers of large amounts of organic molecules, like vegetables in soup Compounds formed by spontaneous reactions energized by solar radiation, volcanic eruption, or lightning Atmosphere believed to be lacking in oxygen Tested in 1953 by Stanley Miller and determined possible under correct conditions The Bubble Model 1986 Louis Lerman suggested key processes for life formation occurred in bubbles on ocean surface Gases from volcanic eruptions trapped in underwater bubbles Chemical reactions in bubbles, protected from UV Bubbles rose and burst, releasing organics Released organics exposed to air and UV to react More complex molecules formed as processes continued to cycle The Evolution of Life Fossils studied to determine evolution of organisms Oldest known fossils 2.5 billion years old Cyanobacteria first marine bacteria to appear Photosynthetic cyanobacteria responsible for development of oxygen in the atmosphere Current atmosphere composed of 21% oxygen Prokaryotes Two groups of prokaryotes developed early Eubacteria with peptidoglycan in cell walls Reamining example E. coli Many disease-causing bacteria Archaebacteria with no peptidoglycan in cell walls Eukaryotes Appeared 1.5 billion years ago Larger, more complex than prokaryotes Mitochondria present in almost all DNA enclosed in nucleus Chloroplasts present in plants and some protists Origins of Mitochondria and Chloroplasts Believed to be result of endosymbiosis Proposed theory in 1966 by Lynn Margulis Mitochondria believed descendants of symbiotic, aerobic eubacteria and choloroplasts descendants of symbiotic, photosynthetic eubacteria Bacteria entered cells and fulfilled roles of cellular respiration or photosynthesis. Believed to be cyanobacteria Support for Endosymbiosis Size and structure of eubacteria and mitochondria and chloroplasts Genetic material similarities Ribosomes Reproduction by fission Multicellularity Organisms grouped into six categories Protists large group of both unicellular and multicellular organisms Protists considered important to development of multi-cellular organisms First multi-cellular organisms found in rocks 700 million years old Three kingdoms resulted – Fungi, Plantae, Animalia Origins of Modern Organisms Most believed to have developed in short time Precambrian and Cambrian periods Time of great evolutionary expansion – Burgess Shale in Canada evidence Ordovician period next – great marine diversity Mass Extinctions Evidence in fossil record of sudden change at end of Ordovician period Many organisms extinct – 5 mass extinctions in Earth’s history Another mass extinction believed to be occurring today due to rapid decline of ecosystems Humans believed cause of current extinction The Theory of Evolution by Natural Selection Idea of evolution first proposed by Roman philosopher Lucretius 1859 English naturalist Charles Darwin published evidence for evolution and suggested a possible mechanism for the process Idea accepted by most scientists as basis for diversity of life on Earth Modern theory built on Darwin’s ideas Before Darwin Belief by most people that each species a divine creation that exists, unchanging, as it was created Darwin’s grandfather a scientist who tried to explain a mechanism for changes over time 1809 French scientist Jean Baptiste Lamarck proposed hypothesis for change in organisms over generations Changes in organisms due to use or disuse of features Changes passed to offspring Belief now known to be faulty Darwin Wealthy family, father a doctor who wanted him to be a doctor or a minister Attended medical school in Scotland but hated surgery, so he changed to become a minister 1831 recommended by professor as naturalist on HMS Beagle Read Charles Lyell’s Principles of Geology on trip that proposed Earth’s surface changed gradually over time and applied this belief to speciesi Darwin Visited Galapogos Islands and noted similarities between animals there and on nearby coasts Developed belief that ancestors of animals migrated and then changed Continued studies on return from voyage Published many years later Growth of Populations 1798 English economist Thomas Malthus wrote that human populations are able to increase faster than the food supply. Unchecked populations grow by geometric progression, while food supplies grow by arithmetic progression. Human populations are checked by death due to disease, war, and famine. Darwin applied this belief to the theory of evolution. Evolution by Natural Selection Limited offspring produced in lifetime, though potential for more Individuals with physical or behavioral traits that better suit their environment are more likely to survive and will reproduce more successfully than those without the traits. Natural selection Adaptation result of challenges and opportunities of different environments. Publication of Darwin’s Work Darwin’s ideas finally written down in 1844 Recent publications about evolution were harshly criticized, so Darwin waited to publish his work until 1858, when a friend was also attempting to be published The papers were presented together at a scientific meeting Darwin’s Theory On the Origin of the Species by Means of Natural Selection, November 1859 Inherited variation within genes of every population or species (random mutation, translational errors) Individuals of population better able to survive and have offspring in a particular environment Over time favorable traits spread in population Evidence from fossils and other sources of evolution of species from extinct organisms Darwin’s Ideas Updated Darwin’s ideas reviewed since publication New discoveries in genetics providing insight into the way natural selection causes evolution Genes responsible for inherited traits Frequency of certain alleles altered by natural selection Sexual reproduction and recombination of alleles key to new variations Species Formation Differences in environment from place to place Species evolved in different directions Reproductive isolation prevents two populations of the same species from breeding. Species that become too different over time incapable of producing offspring Example – Kaibab squirrel on North Rim of Grand Canyon and Abert squirrel on South Rim of Grand Canyon The Tempo of Evolution For decades evolution considered gradual process that occurs continuously (gradualism) Stephen Jay Gould and Niles Eldredge (Americans) suggest successful species may be unchanged for long periods of time Major environmental change cause of evolutionary spurts Periods of little or no change (punctuated equilibrium) Evidence of Evolution Fossil record Change recorded in rocks Older rocks have different species than younger rocks. Three of Darwin’s points widely accepted Earth 4.5 billion years old Organisms living on Earth for most of its history All organisms today share ancestry with earlier, simpler life-forms Formation of Fossils Fossil record incomplete Impossible to form fossils in every environment Hard tissue required Decay rates vary among species. Paleontologists scientists who study fossils Fossils collected and lined up for progressive study of organisms Anatomy and Development Basic similarities in body structures, even when functions differ Vestigial structures evidence of organism’s evolutionary past Homologous structures share a common ancestry, but they exist on two different organisms. Evolutionary history seen in embryo development Biological Molecules Amino acids expected to be similar between organisms that evolved from the same ancestor in the recent past Evolutionary history based on large numbers of gene sequences more reliable – go along more accurately with fossil record Examples of Evolution Environment key factor in determining direction of change Future environmental changes could change the characteristics favorable for survival. Four important points drive natural selection. Factors in Natural Selection All populations have genetic variation. The environment presents challenges to successful reproduction. Individuals tend to produce more offspring than the environment can support. Individuals that are better able to cope with the challenges presented by their environment tend to leave more offspring than those individuals less suited to the environment do. Example Tuberculosis (TB) is the infectious disease that kills the most adults in the world. In the 1950s, two antibiotics wiped out many cases of TB and prevented its spread. New antibiotic-resistant strains of TB have developed, due to genetic variation. The over-use of antibiotics can cause this resistance. Darwin’s Finches 31 specimens of finches collected from three of the Galapagos Islands 9 distinct species, all similar to each other, except their bills (beaks) 2 ground finches with large bills to crush seeds, 2 narrow bills to eat insects, 1 fruit eater, 1 picks insects from cacti, another drinks blood from sea birds All believed by Darwin to have evolved from one species Darwin’s Finches Changes in species as different populations adapted to different food sources Idea tested in 1938 and 1973 and found in second study to be true Numbers of birds with certain characteristics changed by natural selection, as Darwin suggested. Formation of New Species Stages of species formation Changes that improve reproductive success favored by natural selection Divergence is the accumulation of differences between groups, which lead to formation of new species. The process of forming new species is speciation. Subspecies Different populations of species possibly living in different environments Offspring better suited to environment developed through natural selection In vastly different environments, populations can become very dissimilar. Leads to genetic differences and subspecies Eventually different enough that interbreeding impossible Maintaining New Species Eventually new species different enough that interbreeding impossible Can be geographic isolation Different reproduction times Physical differences Changes in attraction Offspring possibly not fertile Offspring possibly not suited to environment of either parent