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CHAPTER 25 CAMPBELL and REECE. Conditions on early Earth made the Origin of Life possible Macroevolution : evolutionary change above the species level.

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Presentation on theme: "CHAPTER 25 CAMPBELL and REECE. Conditions on early Earth made the Origin of Life possible Macroevolution : evolutionary change above the species level."— Presentation transcript:


2 Conditions on early Earth made the Origin of Life possible Macroevolution : evolutionary change above the species level examples: 1. emergence of terrestrial vertebrates 2. mass extinctions impact on diversity of life 3. origin of key adaptations like flight in birds

3 Where did 1st cell come from? 4 main stages could have produced very simple cells: 1. abiotic synthesis of small organic molecules 2. joining of these small molecules into macromolecules (proteins, nucleic acids) 3. packaging of these macromolecules into protocells, droplets with membranes that maintained internal chemistry different from their surroundings 4. origin of self-replicating molecules that eventually made inheritance possible

4 Synthesis of Organic Cpds on early Earth Planets of our solar system formed ~ 4.6 billion yrs ago 1 st few hundred million yrs conditions would not have allowed life on Earth

5 1 st Atmosphere Collisions would have vaporized any water preventing seas from forming Atmosphere thick with gases released from volcanic activity

6 1st Atmosphere 1920’s: Oparin (Russian) & Haldane (British) each came to conclusion early atmosphere was reducing environment (gain e-) in which organic cpds could have formed from simpler molecules

7 1 st Organic Compounds Energy sources: Lightening Thermal energy Intense UV radiation

8 Primordial Soup Haldane had hypothesized the early seas site of 1 st organic compounds  1 st cells Miller & Urey (Univ. of Chicago) in 1950’s Tested Oparin & Haldane ‘s premise Created reducing atmosphere Added cpds considered to have been there

9 Miller & Urey’s Experiment

10 Miller & Urey’s Results

11 repeated using same or similar ingredients, different recipes for the atmosphere  also produced organic compounds ?s about amounts of methane, ammonia (was there really enough to make it a reducing environment?) some repeated experiment in non-reducing, non- oxidizing conditions & still produce organic cpds

12 Miller-Urey Experiment demonstrates: 1. Abiotic synthesis of organic molecules is possible under various assumptions about the composition of Earth’s early atmosphere 2. Meterorites may also have been source of minerals and organic molecules contain amino acids, lipids, simple sugars, uracil

13 Murchison Meteorite

14 fell in so named town in Australia in 1969 large (100 kg) and was quickly retrieved 2010 article published in Scientific American: results of mass spectrometry (separating cpds based on charge & size) have revealed at least 14,000 unique molecules

15 Abiotic Synthesis of Macromolecules 2009 study showed the abiotic synthesis of RNA monomers can occur spontaneously from simpler precursor molecules drip solutions with amino acids (aa) or RNA nucleotides onto hot sand, rock, or clay  polymers of aa & RNA (w/out using enzymes or ribosomes)

16 Protocells Basic characteristics of life : reproduction & metabolism: 1 st cells would have had to be able to reproduce which would have required them to have a source of nitrogenous bases, sugars, phosphate groups now complex enzymes make this all happen

17 Vesicles as 1 st step? When lipids & other organic molecules added to water  vesicles spontaneously form lipid bilayer (separation of hydrophiloic & hydrophobic molecules) these abiotically produced vesicles “reproduce” and grow on their own. clay like from early Earth will be absorbed into the vesicles some vesicles demonstrate semi- permeability

18 Self-Replicating RNA RNA can act as enzyme RNA catalysts called: ribozymes some can make complimentary strands of short pieces of RNA  mutations  more stable &/or successful

19 Ribozyme once self-replicating RNA possible, much easier for further changes to happen. once double-stranded DNA appeared it would have been more stable so RNA left with role we see today

20 The Fossil Record Documents the History of Life

21 The Fossil Record based mostly on sequence in which fossils have accumulated in sedimentary rock strata an incomplete record of evolutionary change (gaps still be filled in) known fossil record biased toward species that: survived for long periods of time were abundant were widespread in certain types of environments made of some hard parts

22 “This could mess up the fossil record, you know.”

23 Tiktaalik extinct closest relative to of 1 st vertebrate to walk on land


25 Radiometric Dating ethod of absolute dating based on decay of radioactive isotopes (1 element  different element + some particle) half-life = rate of decay of ½ the specimen ½ lives are constant & characteristic to each radioactive element outside conditions do not affect rate of decay

26 Dating Fossils C-14 in all living things C-14 decays into N-14 ½ life = 5,730 years measure ratio of C-12 to C-14 left in fossil can only use C-14 dating up to about 75,000 yrs old amt of C-14 left after that so minimal that accuracy becomes an issue if organism dead <500 yrs there to too little to date accurately


28 The 1 st Single-Celled Organisms earliest direct evidence of life date from 3.5 billion years ago from fossilized stromatolites

29 Stromatolites are layered rocks that form when certain prokaryotes (cyanobacteria) bind thin fiolms of sediment together today, found in warm, shallow salty bays reasonable to infer that the bacteria originated much earlier … billion years ago


31 Stromatolites early prokaryotes were Earth’s only living inhabitants from 3.5 to 2.1 billion years ago

32 Photosynthesis & the Oxygen Revolution most of Earth’s atmospheric oxygen is of biologic origin (photosynthesis) at first, O2 would have stayed dissolved in water until concentration high enough to react with Fe in water. water + iron  iron oxide (ppt) these sediment formed banded iron formations

33 Iron Oxide

34 Oxygen once all dissolved Fe ppt out of water the dissolved O2 then released as oxygen gas to atmosphere

35 Rise of Atmospheric Oxygen

36 Rise in Atmospheric Oxygen began ~2.3 billion years ago What caused the rise? probably chloroplasts rising O2 levels would have killed off some anaerobic prokaryotes survivors in environments with low O2 levels Cellular Respiration may have started as adaptation to rising oxygen

37 1 st Eukaryotes oldest accepted eukaryotic fossils: 2.1 billion years

38 Endosymbiont Theory mitochondria & plastids (general term for chloroplasts & related organelles) were once prokaryotes that began living in larger host cells endosymbiont: cell that lives w/in host cell entered cell as undigested prey or internal parasite symbiotic relationship has been recreated w/in 5 yrs using other cells


40 symbiosis mutually beneficial all eukaryotes have mitochondria but not all have plastids soooo Hypothesis: serial endosymbiosis : mitochondria evolved b/4 plastids

41 Evidence Supporting Endosymbiosis inner membranes of mitochondria & plastids have enzymes & transport sytems homologous to those found in plasma membranes of living prokaryotes mitochondria & plastids replicate like prokaryotes each contain a single circular DNA molecule, not ass’c with histones or large amts other proteins (just like bacterial DNA)

42 Evidence Supporting Endosymbiosis both have ribosomes & enzymes to transcribe & translate their DNA  proteins their ribosomes more similar to prokaryotic ribosomes than to eukaryotic cytoplasmic ones

43 Origin of Multicellularity 1st eukaryotes all unicellular organisms common ancestor of multicellular organisms (based on DNA comparisons) lived ~1.5 billion years ago


45 Early Multicellular Organisms 1st appear in fossil record ~ 575 million yrs ago called Ediacaran biota soft bodied up to 1 m in length probably limitied in size & diversity until late Proterozoic due to series of Ice Ages which covered most of Earth’s land mass & seas 750 – 580 million years ago

46 640 million years ago

47 575 million years ago “snowball” Earth thawed 1 st major diversification of multicellular eukaryotes lasted until ~ 40 million years ago

48 Cambrian Explosion

49 b/4 Cambrian Explosion all large animals were soft-bodied little evidence of predation

50 b/4 Cambrian Explosion many animal phyla began pre-Cambrian DNA analysis suggests most animal phyla began to diverge from each other as early as 700 million – 1 billion years ago

51 Colonization of Land fossil evidence of prokaryotes (cyanobacteria & other photosynthetic bacteria) from damp terrestrial surfaces that date well over 1 billion yrs ago 500 million yrs ago: fungi, plants, animals

52 Early Land Plant Adaptations 420 million Yrs Ago internal vascular system for transporting materials but lacked true roots waterproofing to slow loss of water to air (no true leaves)

53 Land Plant Adaptations About 50 million Yrs Ago Plants greatly diversified Reeds Treelike plants with true roots & leaves

54 Arthropods & Tetrapods most widespread & diverse land animals arthropods 1 st land animals (420 million yrs ago) oldest tetrapods 365 million years ago: ancestor lobe-finned fish


56 Arthropod Fossils

57 Early Tetrapods

58 Human Lineage diverged from other primates 6 – 7 million yrs ago our species originated ~ 195,000 yrs ago

59 Plate Tectonics plates of Earth’s crust float on underlying mantle movements in mantle cause plates to move (usually few cm/yr)

60 Plate Boundaries influence formation of mtn ranges, islands, earthquakes when oceanic plate meets continental plate it is subducted under eventually becoming mantle

61 Consequences of Continental Drift alters habitats having large impact on living organisms

62 Pangea formation would have destroyed a considerable amount of marine life habitat (shallow waters) large land mass would have very dry, cold, severe interior formation of Pangea would have caused many extinctions but also opened up opportunities for new species

63 Continental Drift & Climate Change when continent changes location it is bound to change climate 200 million yrs ago Labrador, Canada was in the tropics: species had to adapt, move, or become extinct


65 Effects of Continental Drift promotes allopatric speciation (formation of new species that are geographically separated from one another) on large scale as continents drift apart, each becomes a separate evolutionary arena.

66 Continental Drift Explains Fossil Distribution same fossils found in Brazil & western Africa

67 Mass Extinctions Fossil record shows most species that have ever lived are now extinct. Reasons to become extinct: 1. destroyed habitat 2. changes in environment that did not favor species

68 Mass Extinctions certain times in history environmental changes have caused the normal rate of extinction to increase dramatically = mass extinction 5 Big Mass Extinctions

69 5 Mass Extinctions

70 in the past 500 million years occurred with hard-bodied species for which we have a documented fossil record each one: 50% or more marine species became extinct

71 Mass extinction between Paleozoic & Mesozoic eras claimed ~96% of marine animal species, 8/27 known orders of insects

72 Permian Mass Extinction time of enormous volcanic eruptions in Siberia geologic data indicate 1.6 million km2 covered in hot lava 100’s to 1000’s m thick May have produced enough CO 2 to warm global climate by 6 C  slowed ocean currents  drop in [O 2 ]  ocean anoxia  suffocated O 2 breathers  increase anaerobic bacteria  [H 2 S] (deadly byproduct)  further extinctions on land  ozone layer destroyed  UV radiation increased  more death

73 Cretaceous Mass Extinction ~65.5 million yrs ago between Mezozoic & Cenozoic eras >50% all marine life extinct eliminated all dinosaurs (except birds) Reason? Thin layer of clay enriched in iridium lies between sedimentary rock from the 2 eras. Iridium very rare on Earth but common in meteorites

74 Cretaceaous Mass Extinction Chicxulub Crater off Yucatan penisula is a 65 million year old scar that could have been caused by hit from a comet or asteroid (crater size indicates hit by something 10 km in diameter)

75 6 th Mass Extinction ? Typical “background” rate for extinctions is considered to be 1 – 10 in 400 yrs. There have been > 1,000 extinctions in past 400 yrs Not counting those species (probably some in rain forests) that are becoming extinct that we had never discovered Losses to date have not reached those of the BIG 5

76 Consequences of Mass Extinctions significant & long term effects extinct species is gone forever  course of evolution is changed takes at least 5-10 million yrs for diversity to recover from a mass extinction

77 Mass Extinctions & Ecology

78 Adaptive Radiations Fossil record tells us diversity of life has increased over past 250 million yrs increase largely due to adaptive radiation: periods of evolutionary change in which groups of organisms form many new species to fill different niches Large scale adaptive radiations occurred after each of BIG 5

79 Radiation of Mammals when land dinosaurs became extinct 65.5 million yrs ago mammals moved in and filled the ecological roles or niches now available to them original mammals 180 million yrs ago but they remained small, not very diverse, mostly nocturnal,

80 Development Genes Genes that control development influence the: rate & timing spatial pattern of change in an organism’s form as it develops from zygote  adult

81 Change in Rate & Timing Heterochrony : (Gr: different, time)an evolutionary change in the rate & timing of developmental events Human’s relative shape due in part to relative growth rates of different body parts during development

82 Relative Skull Growth Rates Humans have mutation that slowed growth of jaw relative to other parts of skull produced an adult that looks more similar to chimp fetus than chimp adult

83 Paedomorphosis Adults of some species retain juvenile features of ancestors example: marine salamander axolotl

84 Changes in Spatial Pattern homeotic genes: master regulatory genes that control placement & spatial organization of body parts in animals

85 Hox Genes 1 class of homeotic genes provide positional information in animal embryo

86 Evolution of Development Origin of novel morphological forms likely due to new developmental genes arising from gene duplication events Insects have crustacean-like ancestors that all have more legs ….the Ubx gene is expressed in main trunk of body; in insects it is expressed in abdomen…….in crustacean  legs ….in insects  it suppresses leg formation

87 Ubx Gene mutation Crustacean Body Insect Body

88 Changes in Gene Regulation Harmful Changes can be limited to single cell type may have fewer harmful side effects than point mutations ….so less likely to be a lethal change Marine Stickle back Fish Lake Stickleback Fish

89 Evolution is not Goal Oriented new forms arise by slightly modifying existing forms novel & complex structures can arise as gradual modifications of ancestral structures each step in process of evolving into something complex would have been useful to the species

90 Ranges of Eye Complexity among Molluscs

91 Evolutionary Trends Species Selection Model proposed by Steven Stanley thinks of species as individuals: speciation is their birth, extinction their death new species that diverge from them are their “offspring”. species that last the longest & generate the most new species determine the direction of major evolutionary trends.

92 Species Selection Model

93 Evolutionary Trends Natural Selection still plays a role example: ancestors to modern horse were “browsers” until mid-Cenozoic when grasslands spread across large areas. Horses that were “grazers” and able to run fastest from predators were selected for


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