209 20 13_1


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209 20 13_1

  2. 2. Hadean times conditions <ul><li>The early oceans at the Earth’s surface were probably boiled repeatedly during the primordial meteorite bombardment. </li></ul><ul><li>The craters on the terrestrial planets can be used for stratigraphy purposes. </li></ul>
  3. 3. Nature of data <ul><li>Data from fossils. </li></ul><ul><li>Data from mineralogical composition of the rocks. </li></ul><ul><li>Chemical fossils as results of the organic activity. </li></ul>
  4. 4. The oldest life forms
  5. 5. Stromatolites - generalities <ul><li>The first stromatolites were discovered in the New York State, in the surroundings of Saratoga, in the early 1880s. </li></ul><ul><li>The name of stromatolites was given long after. </li></ul><ul><li>Originally they were named Cryptozoon . </li></ul>
  6. 6. Organic nature of the stromatolites <ul><li>The organic nature of the stromatolites was demonstrated long time after based on the discoveries from southern Ontario. </li></ul><ul><li>Cryptozoon structures were discovered in a point known as Schreiber Beach by Stanley A. Tyler (University of Wisconsin). </li></ul>
  7. 7. Schreiber Beach Cryptozoon
  8. 8. The first Precambrian fossils Eosphaera
  9. 9. The living stromatolites <ul><li>Living stromatolites were discovered in a salty lagoon of western Australia – the Shark Bay. </li></ul>
  10. 10. Fossil & living stromatolites <ul><li>A stromatolite is best studied in polished sections. </li></ul>
  11. 11. Stromatolite morphology
  12. 12. Stromatolite characteristics <ul><li>Accretionary organo-sedimentary structures; </li></ul><ul><li>Thinly layered, megascopic, calcareous; </li></ul><ul><li>Produced by the activity of mat-building communities of mucilage secreting microorganisms; </li></ul><ul><li>Consist mainly of photoautotrophic prokaryotes (e.g., cyanobacteria) </li></ul>
  13. 13. Stromatolite persistence
  14. 14. Stromatolite fossil record <ul><li>Fig Tree Formation of South Africa 3.1 to 3.5 billion years old. </li></ul><ul><li>Just like in the Gunflint Formation of Ontario, the fossils were found in stromatolitic structures. </li></ul>
  15. 15. Stromatolite evolution <ul><li>Stromatolites occurred in the Archean times. At the beginning of their evolution the distribution is patchy. </li></ul><ul><li>They are ubiquitous in the Proterozoic, when the lived in all the environments: streams and rivers, lakes and ponds, seas and oceans. </li></ul><ul><li>Major reduction in frequency at the Precambrian/Cambrian boundary. </li></ul>
  16. 16. Stromatolite evolution <ul><li>Stromatolites represent the living witness of the evolution’s evolution. </li></ul><ul><li>Precambrian times: if not broken, don’t fix it! </li></ul><ul><li>Cambrian to Quaternary: extraordinary diverse morphological changes. </li></ul>
  17. 17. Isolated cells <ul><li>Early Archean of western Australia (Pilbara Craton). </li></ul><ul><li>Apex Chert is a lithological unit in a volcano-sedimentary formation. </li></ul><ul><li>Earliest cyanobacteria debris. </li></ul>
  18. 18. Apex Chert cyanobacteria <ul><li>Some of the cells from the Apex Chert show folded filament with cell-like structures made of carbon. </li></ul><ul><li>Similar to modern iron bacteria. </li></ul>
  19. 19. Strelley Pool Chert cyanobacteria <ul><li>The chain-like structure is similar to that of the modern purple bacteria. </li></ul>
  20. 20. Earth’s rusting <ul><li>Approximately 2.0 billion years ago a major phenomenon happened on Earth. </li></ul><ul><li>Oxides formed in vast amounts (Banded Iron Formation = BIF). </li></ul><ul><li>They document a huge increase in the molecular oxygen in the Earth’s atmosphere. </li></ul>
  21. 21. Prokaryote diversification <ul><li>The first Precambrian fossils were discovered in the Gunflint Formation of southern Ontario. </li></ul><ul><li>Ex: Gunflintia and Huronipora . </li></ul>
  22. 23. Prokaryote <ul><li>Eukaryote cells are much more complex than the prokaryotes. </li></ul>
  23. 24. First eukaryotes <ul><li>The first eukaryotes were discovered in the Bitter Springs Formation of Australia. </li></ul><ul><li>Age: approximately 770 m. y. </li></ul><ul><li>Cell arrangement suggests meiotic cell division. </li></ul><ul><li>Chemical fossils: 1.8 billion years. </li></ul>
  24. 25. Eukaryotes - examples <ul><li>Bangiomorpha </li></ul><ul><li>Filamentous thallus, similar to those of the modern red algae; </li></ul><ul><li>Primitive holdfast attached to the seafloor, allowing the alga to rise upward towards the sunlight. </li></ul><ul><li>Age: ~ 1.2 billion years; </li></ul><ul><li>ST: Proterozoic-Quaternary. </li></ul>
  25. 26. Eukaryotes - examples <ul><li>Torridonophycus </li></ul><ul><li>Algal microstructures escaping from a bag-like structure ( acritarch ), which helped them to survive the dry climate, cold, etc). </li></ul><ul><li>Clorophyte . </li></ul><ul><li>Age: ~ 0.9 billion years. </li></ul><ul><li>ST: Upper Proterozoic-Quaternary. </li></ul>
  26. 27. Eukaryotes - examples <ul><li>Melanocyrillium </li></ul><ul><li>Shows similarities with the modern group of testate amoebas. For this reasons it is included among the earliest animals. </li></ul><ul><li>Organic, sometimes with agglutinated particles. </li></ul><ul><li>Age: ~ 0.8-0.9 billion years. </li></ul><ul><li>ST: Upper Proterozoic-Quaternary. </li></ul>
  27. 28. Kingdoms <ul><li>Bacteria (Prokaryotae, Procaryotae, Monera); prokaryotic cells (lacking a nucleus and nuclear membrane). </li></ul><ul><li>Protoctista (Protista); single eukaryotic cell (with nucleus and nuclear membrane); include foraminifera and radiolaria. </li></ul><ul><li>Animalia (Animals); heterotrophic multicellular eukaryotes (phyla subdivided by cell organization level, symmetry, feeding structures, segmentation, presence of vertebrae or notochord…). </li></ul><ul><li>Plantae (Plants); autotrophic multicellular eukaryotes (algae or aquatic plants and tracheophytes or vascular terrestrial plants). </li></ul><ul><li>Fungi ; (as endoliths in fossil record) heterotrophic eukaryotes with chitinous resistant fungal spores. </li></ul>
  28. 29. Ediacara Hills (southern Australia).
  29. 30. Precambrian Time Scale
  30. 31. Ediacara Animals <ul><li>Animals imprints from Ediacara Hills are all metazoans. They document the transition from the unicellular to multicellular forms of life. </li></ul><ul><li>Ediacaran animals generally present a simple structure, being soft-bodied animals (there is not a trace of skeleton). </li></ul><ul><li>They are worm-like animals (flatworms, segmented worms), coelenterates and some totally unknown types. </li></ul>
  31. 32. Ediacara dominant fossils <ul><li>Parvancorina </li></ul><ul><li>Size: 1-2.5 cm; </li></ul><ul><li>Shield-shaped front end; </li></ul><ul><li>Central axis and weak traces of segmentation; </li></ul><ul><li>Up to 10 pairs of possible appendages with distinct set of growth stages; </li></ul><ul><li>Interesting orientation: head shield(?) facing the direction of water current (feeding strategy?). </li></ul>
  32. 33. Ediacara dominant fossils <ul><li>Tribrachidium </li></ul><ul><li>Unknown affinities; </li></ul><ul><li>2-5 cm; </li></ul><ul><li>Disk-shaped with three raised arms and raised borders; </li></ul><ul><li>Triradial symmetry. </li></ul>
  33. 34. Ediacara dominant fossils <ul><li>Dickinsonia </li></ul><ul><li>1-100 cm; </li></ul><ul><li>Segmented, head, tail (segmented worm?); </li></ul><ul><li>No gut or other internal organs have been found; </li></ul><ul><li>The tail(?) occurs only in the mature specimens. </li></ul>
  34. 35. Ediacara dominant fossils <ul><li>Charnia </li></ul><ul><li>0.15-2 m; </li></ul><ul><li>Strong similarities with the modern sea-pens; </li></ul><ul><li>Bilateral symmetry; </li></ul><ul><li>Feather-shaped frond with a series of side branches. </li></ul>
  35. 36. Ediacaran Animals Today? Living sea-pens from offshore NW Australia.
  36. 37. Ediacara dominant fossils
  37. 38. Spriggina Case <ul><li>A worm-like animal of the Ediacara fauna presents an extraordinary feature. </li></ul><ul><li>In the (probably!) anterior part of its body there is a portion which apparently presents a thickened tissue. </li></ul><ul><li>First evidence of cephalization . See also Parvancorina . </li></ul>
  38. 39. Spriggina Case <ul><li>Approximately 3 cm long. Australia, then Russia. </li></ul>
  39. 40. Controversial Way of Life <ul><li>Seilacher & McMenamin suggested that the animals of Ediacara all lived in symbiotic relationships with algae in their tissues as the modern corals do today. </li></ul><ul><li>Practically the animals of Ediacara-type could get nutrients from the activity of the photosynthetic symbiotic algae. </li></ul>
  40. 41. Vendoza Controversy <ul><li>Seilacher & McMenamin emphasized the dissimilarities between Ediacara-type and modern organisms. </li></ul><ul><li>They also proposed to include the animals of Ediacara into a distinct systematic category: Vendoza . </li></ul><ul><li>The name comes from Vendian , the terminal Neoproterozoic in Russia. </li></ul>
  41. 42. Ediacara Fauna Extinction <ul><li>Ediacara fauna appeared approximately 630 M.y. ago and developed for about 50 M.y. </li></ul><ul><li>It represents the first adaptative radiation of the multicellular organisms. </li></ul><ul><li>Fossil record is patchy. </li></ul><ul><li>Last record : in Ireland some about 510 M.y. </li></ul>
  42. 43. Interpretation dynamics