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Development of Life

Development of Life. George Lebo October 17, 2012 AST 2037. 1. From Last Time: Then … Life Appears!. First fossil cells found in rocks at about T – 3.7 to T – 3.5 Billion Years! Tiny little things Not O 2 breathers like us (none around!) Probably CO 2 breathers

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Development of Life

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  1. Development of Life George Lebo October 17, 2012 AST 2037 1

  2. From Last Time:Then … Life Appears! • First fossil cells found in rocks at about T – 3.7 to T – 3.5 Billion Years! • Tiny little things • Not O2 breathers like us (none around!) • Probably CO2 breathers • Modern cyanobacteria look a lot like these fossils AND they are CO2 breathers • Suggests that the first (fossil) life may have been cyanobacteria (?) 2

  3. Summary • Earth of Way Back When was different • We can tell from chemical and radio-isotope analysis of rocks • Water and other volatiles may have come from comet impacts • Life formed a long time ago – about 3.5 Billion Yr or so • We know from fossils • We don’t know exactly how, but … • We know we had the right elements • Those elements + lightning make amino acids • DNA may have originated from these acids in a clay matrix • Next question: How did things get from Then to Now?? 3

  4. Evolution • This time with a capital “E” • Reproduction occurs via DNA • Any change in the DNA from one generation to the next creates “mutation” • Causes of mutation: • Radiation (all those rock decays; cosmic rays) • Chemical contamination • “Transcription errors” • Random mutation produces wide range of changes • Senescence (Biological Aging) • Apoptosis (Programmed Cell Death) • Unregulated Cell Division (leading to a tumor or to cancer) 4

  5. DNA Mutation • Examples 5

  6. Natural Selection • Some mutations will be competitively “helpful”, some neutral, some disadvantageous • Natural selection: those with competitive “edge” more likely to succeed in reproducing; those without are less likely 6

  7. Natural Selection: Examples • We have seen this in action on even short timescales: • Cockroaches and insecticide • TB bacteria and antibiotics • Light/dark pepper moths in England: • Prior to 1800, mostly light-colored with occasional dark ones (collector items) • After Industrial Revolution, trees darkened by soot, dark ones camouflaged, light ones easy to see • Light ones disappear (eaten by birds!) • Population now dominated by dark moths • This was a hoax. The moths were planted. See museum of hoaxes 7

  8. REQUIREMENTS FOR MUTATIONAL EVOLUTION (ROSS) • MANY INDIVIDUALS (AT LEAST ONE QUADRILLION) • SMALL BODY SIZE (LESS THAN TWO CM.) • SHORT GESTATION PERIOD (LESS THAN THREE MONTHS) • LARGE NUMBER OF PROGENY

  9. FRED HOYLE’S ANALYSIS According to Hoyle's analysis, the probability of cellular life evolving were about one-in-1040000. He commented: The chance that higher life forms might have emerged in this way is comparable to the chance that a tornado sweeping through a junkyard might assemble a Boeing 747 from the materials therein. Life as we know it is, among other things, dependent on at least 2000 different enzymes. How could the blind forces of the primal sea manage to put together the correct chemical elements to build enzymes?[4]

  10. “A THIRD WAY”, JAMES SHAPIRONOT CREATIONISM OR EVOLUTIONISM • Genomes, asserts Shapiro, are not really the static "beads on a string" envisioned by the Darwinians. Rather, they are fluid and complex. Genes are now seen as multipurpose elements that turn on and off as required for the survival and well-being of the organism they belong to.

  11. Back to Early Life • Old fossils – like cyanobacteria • Then … Stromatolites • Lots and lots of stromatolites! 11

  12. Stromatolites • Large agglomerations of single-celled organisms • First they form “microbial mats” (i.e. “pond scum” layer) • These layers live, die, get covered by silt • Next mat forms, etc. • Produces layered fossils 12

  13. Modern Stromatolites • Stromatolites still alive today • Mostly in places where high acidity or salinity in water removes “predators” (i.e. snails and other grazers) 13

  14. Atmospheric Bioengineering • Remember … atmosphere had no O2 to start • At about 2.5 GYA, O2 level jumped • Why? • LOTS of cyanobacteria and other CO2 breathers! 14

  15. Development in the Archaic Era • Time span from 3.6 GYA to about 0.6 GYA • All single-celled life at this time – LOTS of stromatolites • Responsible for the oxygen-enrichment of the atmosphere (liberating O2 from CO2) • Initially prokaryotes – simpler structure, no nucleus • Eukaryotic fossils date to ~2 GYA • Sterol chemicals begin to show up in rocks about ~2.7 GYA • Sterols only known to come from Eukaryotes now (maybe from Eukaryotes or proto-Eukaryotes then) • Still single-celled, but far more complex … 15

  16. Endosymbiotic Theory • Idea that complex eukaryotes formed from symbiotic relationship between simpler prokaryotic cells • In other words, big cell “encapsulates” smaller specialized prokaryotes which form mitochondria, chloroplasts, etc. 16

  17. Endosymbiotic Theory • Evidence for it: • Mitochondria have their own DNA, which is unlike nuclear DNA but similar to prokaryote DNA • Chloroplasts actually resemble cyanobacteria • “Main cell” offered nucleus which stores most of the mitochondria/plastid DNA in a more “protected” environment • Laboratory observations of endosymbiotic relationships developing between some algaes and prokaryotes 17

  18. Single-Celled Evolution • Move from cyanobacteria (simple) to green algae (complex) • From prokaryote to eukaryote • Eukaryotes have 10x to 1,000x more DNA (information for complex structures) • But still … only single-celled life found until ~0.6 GYA • In context: • Life has been around for 3.5 GY • But single-celled for 2.9 GY of it !!! • (for college student scale – as if multi-cell only arrived 3 years ago!) 18

  19. Early Life: Multi-Cellular • Around 600 MYA, start seeing a range of multi-cellular organisms • Seen in sites spread across the world at the same time • Best examples: • The Ediacaran Fauna • Small fossils (typically a few mm to a few cm) • Ediacaran Period is the last geological period of the Neoproterozoic Era 19

  20. Cyclomedusa • Common fossil from this period • Round symmetry; up to 8-10 inches across (!) 20

  21. Tribrachidium • Three-fold symmetry, rather than plain round 21

  22. Spriggina • Later Ediacaran • Bilateral symmetry (familiar?) • Fossils show clear head, mouth • Centralized structure as well • First fossil to show “animal” features 22

  23. Ediacaran Properties • Range of features: • Many have round symmetry • Others have 3-fold symmetry • Later ones show bi-lateral symmetry (like us!) • All “soft-bodied” – vaguely reminiscent of jellyfish and anemones • For early ones, not sure if the moved around or not – could be “filter feeders” • Spriggina sure looks a lot like an “animal” • Few, if any, of the Ediacara left recognizable evolutionary “descendants” seen in modern life 23

  24. Small Shellies • At transition between Edicaran and the upcoming “Cambrian” era, start seeing fossils with hard shells (~550 MYA) • Also start seeing more calcium carbonate and phosphates in the rocks 24

  25. The Cambrian Explosion • Over a period of just a few million years (unresolved in the geological record – meaning it was geologically “instantaneous”) we suddenly see lots of real “animals” • Called the “Cambrian Explosion” (530 MYA) 25

  26. Cambrian Examples • Things that really look like “critters” today (!!) 26

  27. The Burgess Shale • Fossil deposit in western Canada provided first examples • Now many from worldwide 27

  28. The Burgess Shale 28

  29. The Burgess Shale 29

  30. Trilobites • A huge variety of these found in the Cambrian • Look a lot like Horseshoe Crabs (not actually related though!) • Have properties including: • Armor • Legs • Mouth • Eyes (!!) 30

  31. Trilobites 31

  32. Why “Explosion”? • Note the rapid growth in size from a cell, to a few cells (~3 GY); from a few cells to animals (~0.05 GY); from animals to large animals (~0.01 GY) • Over only a few million years (versus BILLIONS before) every currently recognized phylum of life on Earth developed in the Cambrian explosion (!) • Punctuated Equilibrium – Nature remained in a state of “stasis” for long periods of time then, suddenly, a spurt of evolution produced new life forms - Proposed by Steven J. Gould 32

  33. The Cambrian Explosion • Initially, at least, land was still totally barren • No trees, no plants, no critters, no evidence of bacterial life on land either • The sea, on the other hand, was teeming with life! 33

  34. Nature Red in Tooth & Claw • Burgess Shale also provides first conclusive evidence of active predation 34

  35. What Enabled the Cambrian Explosion? • O2 levels jumped to nearly “modern” right before the Cambrian explosion • All modern animals are O2 breathers • Perhaps the O2 increase enabled a dramatic increase in diversity/size of animals 35

  36. What Next? • So far, so good: • We got from bacteria to algae in about 3 billion years (slow progress?) • From algae to jellyfish-like Ediacara in about 50 million years (faster) • From Ediacara to every known phylum and active predators in a few million years (REALLY fast!) • How do we go from there to dinosaurs to US ? • Answer: not in a straight line! 36

  37. Evolutionary Timeline • 530 MYa – first footprint fossil found on land • 505 Mya – first true fish in the sea • 475 MYa – first land plant fossils • 360 MYa -- Beginning of the Carboniferous Age (lots of land plants and trees!) • 360 MYa – First amphibians, followed quickly by first reptiles; insects on land/air; sharks in the ocean 37

  38. Permian Period • 285 MYa to about 250 MYa • Earth would now have been “recognizable” (if somewhat weird!) • Land has immense forests of trees and other plants (but no flowers!) • Ocean has lots of fish (including sharks), marine mammals, still trilobites too 38

  39. Permian Period • Land has insects, amphibians, reptiles • Reptiles could reach sizes of 10-20 feet (!) 39

  40. Permian Period: Pangaea • One of several supercontinents formed over the history of Earth – About one every 500 million years 40

  41. End-Permian • By the late Permian, things seem to be going very well! • Tremendous diversity of life: • Plants and animals • Sea and Land • Then … it all stopped (!) 41

  42. Permian Extinction • AKA “The Great Dying” • 96% of all marine species extinct • 70% of land vertebrates extinct • Note – not individual critters, but entire species! • Overall mortality of living creatures even for “survivor” species might have been >95-99% (!) • “Fungal spike”: • Large jump in fungal fossils after this • Why? lots of dead plant/animal matter! • What caused it ??? – Hypotheses are: • Glaciation of Gondwana • Simultaneous glaciation of the poles • Volcanoes • Formation of Pangaea 42

  43. Mesozoic Era • Defined to begin post-Permian Extinction • Includes Triassic, Jurassic, Cretaceous 44

  44. Mesozoic Era • Big “bounce” in the development of life after the Permian Extinction • Big developments: • Dinosaurs (which come to dominate) • Flowering plants (angiosperms) • Marine reptiles • Flying reptiles • First Mammals • Etc. 45

  45. Mesozoic Dinosaurs 46

  46. Mesozoic Angiosperms 47

  47. Mesozoic Mammals 48

  48. Mesozoic Reptiles 49

  49. Late Cretaceous • Again, unprecedented diversity of life on land and sea • Then (again!) it all ends! • The Cretaceous-Tertiary (K-T) extinction 50

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