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Conditions on early Earth made the origin of life possible
Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages: 1. Abiotic synthesis of small organic molecules 2. Joining of these small molecules into polymers 3. Packaging of molecules into “protobionts” 4. Origin of self-replicating molecules
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Synthesis of Organic Compounds on Early Earth
Earth formed about 4.6 billion years ago, along with the rest of the solar system Earth’s early atmosphere contained water vapor and chemicals released by volcanic eruptions Experiments simulating an early Earth atmosphere produced organic molecules from inorganic precursors, but such an atmosphere on early Earth is unlikely
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CH4 Water vapor Electrode NH3 H2 Condenser Cold water Cooled water containing organic molecules H2O Sample for chemical analysis
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Instead of forming in the atmosphere, the first organic compounds may have been synthesized near submerged volcanoes and deep-sea vents Some organic compounds from which the first life on Earth arose may have come from space Carbon compounds have been found in some meteorites that landed on Earth Small organic molecules polymerize when they are concentrated on hot sand, clay, or rock
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Protobionts Protobionts are aggregates of abiotically produced molecules surrounded by a membrane or membrane-like structure Experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds For example, small membrane-bounded droplets called liposomes can form when lipids or other organic molecules are added to water
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Glucose-phosphate 20 mm Glucose-phosphate Phosphorylase Starch Amylase Phosphate Maltose Maltose Simple reproduction Simple metabolism
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The “RNA World” and the Dawn of Natural Selection
The first genetic material was probably RNA, not DNA RNA molecules called ribozymes have been found to catalyze many different reactions, including: Self-splicing Making complementary copies of short stretches of their own sequence or other short pieces of RNA
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Ribozyme (RNA molecule) 3¢ Template 3¢ Nucleotides Complementary RNA copy 5¢ 5¢
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Early protobionts with self-replicating, catalytic RNA would have been more effective at using resources and would have increased in number through natural selection
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Fossil study opens a window into the evolution of life over billions of years
Sedimentary strata reveal the relative ages of fossils Index fossils are similar fossils found in the same strata in different locations They allow strata at one location to be correlated with strata at another location
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The absolute ages of fossils can be determined by radiometric dating
The magnetism of rocks can provide dating information Magnetic reversals of the magnetic poles leave their record on rocks throughout the world
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Ratio of parent isotope
Accumulating “daughter” isotope Ratio of parent isotope to daughter isotope 1 2 Remaining “parent” isotope 1 4 1 8 1 16 1 2 3 4 Time (half-lives)
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The Geologic Record The geologic record is divided into three eons: the Archaean, the Proterozoic, and the Phanerozoic The Phanerozoic eon is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic Each era is a distinct age in the history of Earth and its life, with boundaries marked by mass extinctions seen in the fossil record Lesser extinctions mark boundaries of many periods within each era
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Mass Extinctions The fossil record chronicles a number of occasions when global environmental changes were so rapid and disruptive that a majority of species were swept away
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Millions of years ago 600 500 400 300 200 100 100 2,500 Number of taxonomic families 80 2,000 Permian mass extinction ) Extinction rate 60 1,500 Number of families ( Extinction rate ( 40 1,000 Cretaceous mass extinction ) 20 500 Cambrian Ordovician Silurian Devonian Carboniferous Permian Triassic Jurassic Cretaceous Paleogene Proterozoic eon Neogene Ceno- zoic Paleozoic Mesozoic
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The Permian extinction killed about 96% of marine animal species and 8 out of 27 orders of insects
It may have been caused by volcanic eruptions The Cretaceous extinction doomed many marine and terrestrial organisms, notably the dinosaurs It may have been caused by a large meteor impact Mass extinctions provided life with unparalleled opportunities for adaptive radiations into newly vacated ecological niches
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NORTH AMERICA Chicxulub crater Yucatán Peninsula
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Ceno- zoic Meso- zoic Humans Paleozoic Land plants Animals Origin of solar system and Earth 1 4 Proterozoic Eon Archaean Eon Billions of years ago 2 3 Multicellular eukaryotes Prokaryotes Single-celled eukaryotes Atmospheric oxygen
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As prokaryotes evolved, they exploited and changed young Earth
The oldest known fossils are stromatolites, rocklike structures composed of many layers of bacteria and sediment Stromatolites date back 3.5 billion years ago Prokaryotes were Earth’s sole inhabitants from 3.5 to about 2 billion years ago
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Electron Transport Systems…Photosynthesis and the Oxygen Revolution
Electron transport systems were essential to early life Oxygenic photosynthesis probably evolved about 3.5 billion years ago in cyanobacteria
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Effects of oxygen accumulation in the atmosphere about 2
Effects of oxygen accumulation in the atmosphere about 2.7 billion years ago: Posed a challenge for life Provided opportunity to gain energy from light Allowed organisms to exploit new ecosystems
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Eukaryotic cells arose from symbioses and genetic exchanges between prokaryotes
Among the most fundamental questions in biology is how complex eukaryotic cells evolved from much simpler prokaryotic cells The oldest fossils of eukaryotic cells date back 2.1 billion years
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The theory of endosymbiosis proposes that mitochondria and plastids were formerly small prokaryotes living within larger host cells The prokaryotic ancestors of mitochondria and plastids probably gained entry to the host cell as undigested prey or internal parasites In the process of becoming more interdependent, the host and endosymbionts would have become a single organism
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Cytoplasm DNA Plasma membrane Ancestral prokaryote Infolding of plasma membrane Endoplasmic reticulum Nuclear envelope Nucleus Engulfing of aerobic heterotrophic prokaryote Cell with nucleus and endomembrane system Mitochondrion Mitochondrion Engulfing of photosynthetic prokaryote in some cells Ancestral heterotrophic eukaryote Plastid Ancestral photosynthetic eukaryote
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Key evidence supporting an endosymbiotic origin of mitochondria and plastids:
Similarities in inner membrane structures and functions Both have their own circular DNA
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Eukaryotic Cells as Genetic Chimeras
Endosymbiotic events and horizontal gene transfers may have contributed to the large genomes and complex cellular structures of eukaryotic cells Eukaryotic flagella and cilia may have evolved from symbiotic bacteria, based on symbiotic relationships between some bacteria and protozoans
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50 mm
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150 mm 200 mm Two-celled stage of embryonic development (SEM)
Later embryonic stage (SEM)
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Continental Drift The continents drift across our planet’s surface on great plates of crust that float on the hot underlying mantle These plates often slide along the boundary of other plates, pulling apart or pushing each other Many important geological processes occur at plate boundaries or at weak points in the plates
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Eurasian Plate North American Plate Philippine Plate Juan de Fuca Plate Caribbean Plate Arabian Plate Indian Plate Cocos Plate South American Plate Pacific Plate Nazca Plate African Plate Australian Plate Scotia Plate Antarctic Plate
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Volcanoes and volcanic islands Trench Oceanic ridge Subduction zone Oceanic crust Seafloor spreading
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The formation of the supercontinent Pangaea during the late Paleozoic era and its breakup during the Mesozoic era explain many biogeographic puzzles
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By about 10 million years ago, Earth’s youngest major mountain range, the Himalayas, formed as a result of India’s collision with Eurasia during the Cenozoic. The continents continue to drift today. Cenozoic Molecular data have provided insights into the deepest branches of the tree of life North America Eurasia By the end of the Mesozoic, Laurasia and Gondwana separated into the present-day continents. 65.5 Africa South America India Madagascar Australia Antarctica Laurasia By the mid-Mesozoic Pangaea split into northern (Laurasia) and southern (Gondwana) landmasses. 135 Gondwana Millions of years ago Mesozoic At the end of the Paleozoic, all of Earth’s landmasses were joined in the supercontinent Pangaea. 251 Pangaea Paleozoic
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Previous Taxonomic Systems
Early classification systems had two kingdoms: plants and animals Robert Whittaker proposed five kingdoms: Monera, Protista, Plantae, Fungi, and Animalia
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Plantae Fungi Animalia Eukaryotes Protista Prokaryotes Monera
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Reconstructing the Tree of Life: A Work in Progress
The five kingdom system has been replaced by three domains: Archaea, Bacteria, and Eukarya Each domain has been split into kingdoms
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Chapter 27 Chapter 28 Red algae Chlorophytes Charophyceans Proteobacteria Chlamydias Spirochetes Cyanobacteria Gram-positive bacteria Korarchaeotes Cercozoans, radiolarians Diplomonads, parabasalids Euglenozoans Euryarchaeotes, crenarchaeotes, nanoarchaeotes Alveolates (dinoflagellates, apicomplexans, ciliates) Stramenopiles (water molds, diatoms, golden algae, brown algae) Domain Archaea Domain Eukarya Domain Bacteria Universal ancestor
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Chapter 29 Chapter 30 Chapter 28 Chapter 31 Chapter 32 Chapters 33, 34 Chytrids Angiosperms Zygote fungi Sac fungi Club fungi Sponges Choanoflagellates Cnidarians (jellies, coral) Arbuscular mycorrhizal fungi Seedless vascular plants (ferns) Gymnosperms Bryophytes (mosses, liverworts, hornworts) Amoebozoans (amoebas, slime molds) Bilaterally symmetrical animals (annelids, arthropods, molluscs, echinoderms, vertebrates) Plants Animals Fungi
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Animations and Videos Bozeman - Origin of Life Bozeman – Abiogenesis
Synthesis of Prebiotic Molecules Miller Urey Experiment Bozeman - Biotic and Abiotic Factors Endosymbiosis Bozeman – Endosymbiosis Evolution of Organelles
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Animations and Videos The Simplest Eukaryotes Pasteur's Experiment
Bozeman - Classification of Life Three Domains Bozeman - The Three Domains of Life Bozeman – Biodiversity Chapter Quiz Questions – 1 Chapter Quiz Questions – 2
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Which of the following taxonomic categories includes the fewest number of species?
Animalia Panthera Felidae Carnivora Mammalia Answer: B
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Which of the following taxonomic categories includes the fewest number of species?
Animalia Panthera Felidae Carnivora Mammalia 47
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Animals that possess homologous structures probably _____.
evolved from the same ancestor are headed for extinction by chance had similar mutations in the past are not related have increased genetic diversity Answer: A 48
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Animals that possess homologous structures probably _____.
evolved from the same ancestor are headed for extinction by chance had similar mutations in the past are not related have increased genetic diversity 49
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Which of the following would make the most suitable outgroup species for a cladogram relative to all the other species? frog tuna snake penguin bat Answer: B The other choices are descended from terrestrial vertebrates. 50
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Which of the following would make the most suitable outgroup species for a cladogram relative to all the other species? frog tuna snake penguin bat 51
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Which principle is not used to identify phylogenetic relationships?
maximum parsimony Occam’s razor maximum likelihood minimum analogy Answer: D 52
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Which principle is not used to identify phylogenetic relationships?
maximum parsimony Occam’s razor maximum likelihood minimum analogy 53
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Given the DNA sequence data in the table, which phylogenetic tree is the most parsimonious?
Answer: A 54
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Given the DNA sequence data in the table, which phylogenetic tree is the most parsimonious?
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Which of the following is the correct way to write the scientific name for humans?
Homo sapiens homo sapiens Answer: C The name should be written in italics with the genus capitalized and the species lowercase. 56
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Which of the following is the correct way to write the scientific name for humans?
Homo sapiens homo sapiens 57
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When describing a group of animals, you speak about an ancestral species and some but not all of its descendants. This is an example of a monophyletic group. polyphyletic group. paraphyletic group. Answer: C A monophyletic group is an ancestor and all of its descendants, and a polyphyletic group is a group that has multiple ancestors. 58
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When describing a group of animals, you speak about an ancestral species and some but not all of its descendants. This is an example of a monophyletic group. polyphyletic group. paraphyletic group. 59
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Hair on mammals when compared to other vertebrates is an example of a
shared derived character. shared ancestral character. paraphyletic character. polyphyletic character. Answer: A Hair is something that only mammals share, and it is not found in their ancestors. If it were, then we would call it a shared ancestral character. 60
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Hair on mammals when compared to other vertebrates is an example of a
shared derived character. shared ancestral character. paraphyletic character. polyphyletic character. 61
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Which of the following broad taxonomic groups is not one of the three domains of life?
Bacteria Archaea Plantae Eukarya Answer: C 62
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Which of the following broad taxonomic groups is not one of the three domains of life?
Bacteria Archaea Plantae Eukarya 63
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Scientific Skills Exercise
Researchers have long debated different hypotheses for the phylogeny and classification of species in the bear family, Ursidae. In 2008, researchers obtained complete mitochondrial DNA (mtDNA) genome sequences for the eight living species of bears. Based on these data, the researchers constructed a phylogenetic tree for the family Ursidae. (See next slide.)
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Which branch point represents the most recent common ancestor of all bears?
The most recent common ancestor to all living bears is not shown in this tree. Answer: A
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Which branch point represents the most recent common ancestor of all bears?
The most recent common ancestor to all living bears is not shown in this tree.
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Which branch point represents the most recent common ancestor of the sloth bear and the spectacled bear? branch point 1 branch point 2 branch point 3 The sloth bear and the spectacled bear do not share a common ancestor. Answer: B
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Which branch point represents the most recent common ancestor of the sloth bear and the spectacled bear? branch point 1 branch point 2 branch point 3 The sloth bear and the spectacled bear do not share a common ancestor.
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Which branch point represents the most recent common ancestor of the Asian black bear and the brown bear? branch point 2 branch point 3 branch point 4 branch point 5 Answer: C
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Which branch point represents the most recent common ancestor of the Asian black bear and the brown bear? branch point 2 branch point 3 branch point 4 branch point 5
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Which species is the basal taxon in this tree?
the polar bear the spectacled bear the sloth bear the giant panda Answer: D
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Which species is the basal taxon in this tree?
the polar bear the spectacled bear the sloth bear the giant panda
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Identify the sister taxon to the polar bear.
the brown bear the ancestor represented by branch point 7 the Asian black bear the American black bear Answer: A
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Identify the sister taxon to the polar bear.
the brown bear the ancestor represented by branch point 7 the Asian black bear the American black bear
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According to this tree, is the sun bear more closely related to the sloth bear or the polar bear?
The sloth bear and the polar bear are equally distant relatives of the sun bear. Answer: A
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According to this tree, is the sun bear more closely related to the sloth bear or the polar bear?
The sloth bear and the polar bear are equally distant relatives of the sun bear.
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The tree includes the most recent common ancestor of all living species of bears (branch point 1). What does this tell you about this phylogenetic tree? This phylogenetic tree contains homoplasies. This phylogenetic tree is rooted. The Ursidae family is a paraphyletic group. The Ursidae family is a polyphyletic group. Answer: B
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The tree includes the most recent common ancestor of all living species of bears (branch point 1). What does this tell you about this phylogenetic tree? This phylogenetic tree contains homoplasies. This phylogenetic tree is rooted. The Ursidae family is a paraphyletic group. The Ursidae family is a polyphyletic group.
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Which of the following groups of species is a monophyletic group, or clade?
all species of living bears brown bear, polar bear, ancestral species 4, ancestral species 7 sun bear, Asian black bear, American black bear, ancestral species 5, ancestral species 6 sun bear, sloth bear, spectacled bear Answer: C
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Which of the following groups of species is a monophyletic group, or clade?
all species of living bears brown bear, polar bear, ancestral species 4, ancestral species 7 sun bear, Asian black bear, American black bear, ancestral species 5, ancestral species 6 sun bear, sloth bear, spectacled bear
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