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Chapter 26

Chapter 26. The Tree of Life An Introduction to Biological Diversity. Overview: Changing Life on a Changing Earth Life is a continuum, e xtending from the earliest organisms to the great variety of species that exist today. Earth formed about 4.6 Billion years ago.

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Chapter 26

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  1. Chapter 26 The Tree of LifeAn Introduction to Biological Diversity

  2. Overview: Changing Life on a Changing Earth • Life is a continuum, extending from the earliest organisms to the great variety of species that exist today

  3. Earth formed about 4.6 Billion years ago • Early Earth’s atmosphere contained • Water vapor (H2O) • Nitrogen (N2) • Carbon dioxide (CO2) • Hydrogen (H2) • Methane (CH4) • Ammonia (NH3) • Hydrogen sulfide (H2S) • Carbon monoxide (CO) • No O2, why? Because it is too reactive • Volcanic eruptions and asteroid bombardment persisted for the first 800 Million years • Around 3800 MYA Earth cools enough to have liquid water condense.

  4. Liquid water is VERY Important for life • Why? Because interesting chemistry can happen in water • Molecules are moving fast enough to collide and react, but not so fast that they break apart as soon as a new molecule forms • As you can see the earliest evidence of life is observed 3500 MYA, only 300 million years after liquid water appears on earth.

  5. What is the earliest physical evidence if life?Stromatolites: 3.5 Billion year old fossilized bacterial mats • 1. Scientists Lynn Margulis and Kenneth Nealson are shown collecting bacterial mats in a Baja California lagoon. • 3. Some bacterial mats form rock like structures called stromatolites, • Below: Shark Bay, Western Australia, 3000 year old stromatolites • 2. A section through a mat shows layers of sediment that adhere to the sticky bacteria as the bacteria migrate upward. • 4. This is a section of a fossilized stromatolite that is about 3.5 billion years old. • Figure 26.11a, b

  6. Handout: Introduction to Biological Molecules

  7. What was happening in the 300 Million years between when liquid water forms and the first prokaryotic cells appear? • Organic molecules needed for life formed through chemical reactions on early earth. • What are the molecules needed for life?

  8. How could early earth have formed these molecules? • The necessary elements were present in the simple molecules in early earths atmosphere: • H2O, N2, CO2, H2 , CH4, NH3, H2S, CO, • PO4 is a common salt found in rocks and soil. • All that is needed is time and energy for chemical reactions to occur to make more complex molecules

  9. CH4 • Electrode Miller and Urey’s Experimental Design • Water vapor • Simulated conditions thought to have existed on early Earth. • H2 • NH3 • EXPERIMENT • Condenser • RESULTS • Cold • water • As material circulated through the apparatus, samples were collected for analysis. • They identified a variety of organic molecules, including amino acids and complex, oily hydrocarbons. • Cooled water • containing • organic • molecules • H2O • CONCLUSION • Sample for • chemical analysis • Organic molecules, a first step in the origin of life, can form from conditions similar to early earth • Figure 26.2

  10. Other Hypotheses for how biological molecules could have formed • Under water near deep sea hydrothermal vents • Ice: ice has been shown to catalyze formation of ribozymes, or “RNA Enzymes” • Space on asteroids: Amino ccidshave been found on meteorites. • Figure 26.3

  11. Steps involving evolution of life • Simple inorganic molecules form biological macromolecules • Biological macromolecules form polymers. • Self Replicating RNAs were likely the first genetic material because they can function as enzymes and genetic information. • Self Replicating RNAs compete and the ones that function best in self replication increase in numbers • A primitive metabolism evolves • Self replicating RNA become packaged into membrane forming protocells. • DNA replaces RNA as the genetic material (it is more stable) RNA remains critical for translation of protein.

  12. Evidence for the RNA world hypothesis • Ribozyme • (RNA molecule) • 3′ • Template • RNA molecules called ribozymes have been found to catalyze many different reactions, including • Self-splicing (cutting and pasting RNA together) • Making complementary copies of short stretches of their own sequence or other short pieces of RNA • Nucleotides • Figure 26.5 • 5′ • 5′ • Complementary RNA copy

  13. Glucose-phosphate Protocells • 20 μm • Glucose-phosphate • Phosphorylase • Starch • Amylase • Phosphate • Maltose • Maltose • (a) Simple reproduction. This lipo-some is “giving birth” to smallerliposomes (LM). • (b) Simple metabolism. If enzymes—in this case, phosphorylase and amylase—are included in the solution from which the droplets self-assemble, some liposomes can carry out simple metabolic reactions and export the products. • Figure 26.4a, b

  14. From simple Protocells to complex Eukaryotic Cells Early life was simple: genetic material, bound in a lipid membrane, simple metabolism, ribosomes to make proteins Bacterial life leaves its traces starting 3.5 Billion Years ago 2.7 BYA Photosynthetic Bacteria transform the atmosphere by producing oxygen 2.1 BYA Eukaryotic Cells Evolved through Endosymbiosis The theory of endosymbiosis proposes that mitochondria and plastids were formerly small prokaryotes living within larger host cells

  15. The evidence supporting an endosymbiotic origin of mitochondria and plastids includes • Similarities in inner membrane structures and functions • Both have their own circular DNA • Mitochondrial and Chloroplasts have ribosomes more similar to bacterial TEM of free-living Cyanobacteria TEM of Chloroplast

  16. 1.2 BYA Multicellularity evolved several times in eukaryotes • Bacteria had evolved mechanisms of cellular communication • Eukarya had larger more complex cells and more complex genomes. and sexual reproduction. • Eukarya were complex enough to evolve multicellularity • Multicellularity= Specialization of cell structure and function!

  17. So What does the Tree of Life Look Like?

  18. Ceno-zoic • Meso-zoic • Paleozoic • Humans • The analogy of a clock • Can be used to place major events in the Earth’s history in the context of the geological record • Land plants • Origin of solar • system and • Earth • Animals • 4 • 1 • Proterozoic • Eon • Archaean • Eon • Billions of years ago • 2 • 3 • Multicellular • eukaryotes • Prokaryotes • Single-celled • eukaryotes • Figure 26.10 • Atmospheric • oxygen

  19. The absolute ages of fossils • Can be determined by radiometric dating • Accumulating “daughter” isotope • 1 • 2 • Ratio of parent isotope to daughter isotope • 1 • 4 • Remaining “parent” isotope • 1 • 8 • 1 • 16 • 1 • 2 • 3 • 4 • Time (half-lives) • Figure 26.7

  20. 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 • Millions of years ago • 600 • 400 • 300 • 200 • 500 • 100 • 0 • 2,500 • 100 • Number of • taxonomic • families • 80 • 2,000 • Permian mass • extinction • Extinction rate • 60 • 1,500 • Extinction rate ( ) • Number of families ( ) • 40 • 1,000 • Cretaceous • mass extinction • 500 • 20 • 0 • 0 • Carboniferous • Neogene • Cretaceous • Ordovician • Paleogene • Devonian • Cambrian • Permian • Jurassic • Silurian • Proterozoic eon • Triassic • Ceno- • zoic • Figure 26.8 • Paleozoic • Mesozoic

  21. Two major mass extinctions, the Permian and the Cretaceous • Have received the most attention • The Permian extinction • Claimed about 96% of marine animal species and 8 out of 27 orders of insects • Is thought to have been caused by enormous volcanic eruptions

  22. NORTH • AMERICA • The Cretaceous extinction • Doomed many marine and terrestrial organisms, most notably the dinosaurs • Is thought to have been caused by the impact of a large meteor • Chicxulub • crater • Yucatán • Peninsula • Figure 26.9

  23. Much remains to be learned about the causes of mass extinctions • But it is clear that they provided life with unparalleled opportunities for adaptive radiations into newly vacated ecological niches

  24. The Earliest Multicellular Eukaryotes • Molecular clocks • Date the common ancestor of multicellular eukaryotes to 1.5 billion years • The oldest known fossils of eukaryotes • Are of relatively small algae that lived about 1.2 billion years ago

  25. Larger organisms do not appear in the fossil record • Until several hundred million years later • Chinese paleontologists recently described 570-million-year-old fossils • That are probably animal embryos • Figure 26.15a, b • (a) Two-cell stage • (b) Later stage • 150 μm • 200 μm

  26. The Colonial Connection • The first multicellular organisms were colonies • Collections of autonomously replicating cells • 10 μm • Figure 26.16

  27. The “Cambrian Explosion” • Most of the major phyla of animals • Appear suddenly in the fossil record that was laid down during the first 20 million years of the Cambrian period

  28. Phyla of two animal phyla, Cnidaria and Porifera • Are somewhat older, dating from the late Proterozoic • 500 • Annelids • Sponges • Molluscs • Chordates • Cnidarians • Arthropods • Brachiopods • Echinoderms • Early • Paleozoic • era • (Cambrian • period) • Millions of years ago • 542 • Late • Proterozoic • eon • Figure 26.17

  29. Molecular evidence • Suggests that many animal phyla originated and began to diverge much earlier, between 1 billion and 700 million years ago

  30. Continental Drift • Earth’s continents are not fixed • They drift across our planet’s surface on great plates of crust that float on the hot underlying mantle

  31. Eurasian Plate • North • American • Plate • Often, these plates slide along the boundary of other plates • Pulling apart or pushing against each other • Juan de Fuca • Plate • Caribbean • Plate • Philippine • Plate • Arabian • Plate • Indian • Plate • Cocos Plate • South • American • Plate • Pacific • Plate • Nazca • Plate • African • Plate • Australian • Plate • Scotia Plate • Antarctic • Plate • Figure 26.18

  32. India collided with • Eurasia just 10 million • years ago, forming the • Himalayas, the tallest • and youngest of Earth’s • major mountain • ranges. The continents • continue to drift. • 0 • The formation of the supercontinent Pangaea during the late Paleozoic era • And its breakup during the Mesozoic era explain many biogeographic puzzles • Cenozoic • Eurasia • North America • By the end of the • Mesozoic, Laurasia • and Gondwana • separated into the • present-day continents. • 65.5 • Africa • India • South • America • Madagascar • Australia • Antarctica • By the mid-Mesozoic, • Pangaea split into • northern (Laurasia) • and southern • (Gondwana) • landmasses. • Laurasia • Millions of years ago • 135 • Gondwana • Mesozoic • At the end of the • Paleozoic, all of • Earth’s landmasses • were joined in the • supercontinent • Pangaea. • 251 • Pangaea • Paleozoic • Figure 26.20

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