1. The Precambrian Record

2. Key Events of Precambrian time Acasta Gneiss is dated at 3.96 bya. It is near Yellowknife Lake, NWT Canada Zircons possibly a bit older in Australia

3. Precambrian 4.6 billion years to, say, 548 or 544 million years (depending on method). Represents 88% of all of the history of the earth. Referred to as the Cryptozoic Eon. –“hidden life” (prokaryotes) (no more BIFs) Hadean (oldest ) Archean Proterozoic

4. Early Hadean Highlights 1 Earth formed about 4.6 billion years ago from coalescing interstellar dust.Earth formed about 4.6 billion years ago from coalescing interstellar dust. Earth was bombarded by large planetesimals adding to earth’s mass (adds heat)Earth was bombarded by large planetesimals adding to earth’s mass (adds heat) Hot spinning pre-earth mass melted, caused differentiation of materials according to density.Hot spinning pre-earth mass melted, caused differentiation of materials according to density. Distinct earth layers begin to formDistinct earth layers begin to form –Dense iron and nickel sink to center forms core. –silicate material floats up, forms mantle

5. Early Hadean Highlights 2 Huge impact from a Mars-sized planetessimal created the moon.Huge impact from a Mars-sized planetessimal created the moon. –Caused earth to spin faster. –Possible Tilt change –Moon controls earth’s spin and creates tidal forces. –Moon’s orbit at an angle to planets around Sun –Earth got most of the core – outer part molten. Earth rotates. We have magnetic field and, therefore, an atmosphere

6. Moon Origin hypotheses -1 Speed and approach angle unlikely.

7. Moon Origin hypotheses - 2 Does not explain the depletion of metallic iron in the Moon

8. Moon Origin hypotheses - 3

9. Precambrian Early Atmosphere Precambrian Early Atmosphere First earth atmosphere H He. Lost to solar wind. No magnetic field. Post-differentiation start of liquid core induced magnetic field Early permanent earth atmosphere mostly N 2 CO 2 H 2 O gasses from volcanic outgassing. Not lost-protected by magnetic field Liquid water is required to remove CO 2 from atmosphere. –Mars is too cold to have liquid water. –Venus is too hot to have liquid water. –So both have CO 2 atmospheres. On Earth, most of the world’s CO 2 was converted to O 2 by photosynthesis. Enough by 2.0 bya CO 2 is locked up in life, limestones, dolomites! MarsEarthVenus

10. Gasses from cooling magmas formed early atmosphere mostly N 2, CO 2, with CH 4, H 2 O Earth not conducive to modern oxygen breathing organisms: too much UV. Little oxygen O 2 occurred in the atmosphere until the evolution of photosynthetic organisms (Eubacteria) 3.5 billion years ago. Fully oxygenated about 1.9 billion years ago. Early Permanent Atmosphere Sulphur Dioxide from Kilauea

11. Precambrian Early Oceans from 4 bya Much water vapor from volcanic degassing. Salt in oceans is derived from weathering and carried to the oceans by rivers. Blood of most animals has chemistry of seawater. Part of the earth’s water probably came from comets. –Comets are literally large dirty snowballs. –Provide fresh water. OCEANS

12. Archean To Proterozoic Sedimentary Rocks Archean To Proterozoic Sedimentary Rocks Archean 3.8 bya: mostly deep water clastic deposits such as mudstones and muddy sandstones. –high concentration of eroded volcanic minerals (Sandstones called Graywackes). 3 bya: absence of shallow water shelf carbonates. –increasing chert. – low oxygen levels, free iron was much more common in the Archean. –Iron formed “chemical sinks” that consumed much of the early planetary oxygen. –Formed banded ironstones, commonly with interbedded chert. Proterozoic – 2 bya Carbonates become important - Non-marine sediments turn red – iron is oxidized by the oxygen in AIR

13. Precambrian Hadean Formation of Continents Early earth surface was magma sea, gradually cooled to form the crust. Continents did not always exist but grew from the chemical differentiation of early, mafic magmas in the young hot earth. Floating “Volcanic Islands” of less dense higher silica magmas.

14. Precambrian: Hadean and Archean Formation of Felsic Islands Convection fast due high temperatures – ultramafic melts. Partial Melting of base makes new melt, fractionates, melt higher Silica SiO 2.piles up, stack thickens. Base deeper, melts, fractionation leaves melt richer in silica. Silica-rich melts have a lower density, float up. Partial Melting of base makes new melt, fractionates, melt higher Silica SiO 2. Lava piles up, stack thickens. Base deeper, melts, fractionation leaves melt richer in silica. Silica-rich melts have a lower density, float up. Increasing amounts of Felsic continental material, form protocontinents.Increasing amounts of Felsic continental material, form protocontinents. Once rocks with different densities exist, subduction of low silica rocks under higher silica protocontinents is possible. Once rocks with different densities exist, subduction of low silica rocks under higher silica protocontinents is possible. Water squeezed from subducted ocean materials partially melts mantle, magma rises, fractionates and assimilates. Continents build up, they are too bouyant to be subducted. Water squeezed from subducted ocean materials partially melts mantle, magma rises, fractionates and assimilates. Continents build up, they are too bouyant to be subducted.

15. First continental crust 3.Density differences allow subduction of mafic rocks. Further partial melting and fractionation makes higher silica melt that won’t subduct Water out 2. Komatiite partially melts, Basalt gets to surface, piles up. The stack sinks, base partially melts when pressure high enough. Fractionation makes increasingly silica-rich magmas First Then: 1.At high temperatures, only Olivine and Ca-Plagioclase crystallize “Komatiite”

16. Archean: Growth of the early continents Magmatism from Subduction Zones causes thickening

17. Growth of the early continents Island Arcs and other terranes accrete to edge of small continents as intervening ocean crust is subducted. Temps so high that convection is intense, divergence breaks up protocontinents. Little Archean ocean crust survives: most was subducted

18. Growth of the early continents Sediments extend continental materials seaward

19. Growth of the early continents Continent-Continent collisions result in larger continents Again, not very big in Archean; convection cells too small

20. Archean-Age Surface Rocks

21. Precambrian Early Continents (Cratons) Archean Archean cratons consist of regions of light-colored felsic rock (granulite gneisses) surrounded by pods of dark-colored greenstone (chlorite-rich metamorphic rocks). –Pilbara Shield, Australia –Canadian Shield –South African Shield. Greenstone Belts Felsic Islands 40km

22. Archean Crustal Provinces were once separated Canadian Shield assembled from small cratons Intensely folded rocks, now planed off flat, where cratons were later sutured together in Early Proterozoic Longest: Trans-Hudson Orogen

24. Granulite gneiss and greenstone Canadian Shield Exposed by Pleistocene glaciers

25. Stratigraphic Sequence of a Greenstone belt Younger lavas richer in silica Komatiites form at very high temps. They are absent later as Earth cooled Increasingly Silica-rich extrusives, some rhyolites with granites below them. Banded Iron Formations DEMO: Banded Iron Sample Note similarity to modern Ophiolite

26. Archean Formation of greenstone belts Early continents formed by collision of felsic proto-continents. Greenstone belts represent volcanic rocks and sediments that accumulated in ocean basins, then were sutured to the protocontinents during collisions. Protocontinents small, rapid convection breaks them up

28. Proterozoic Tectonics: The Wilson Cycle Proterozoic – Convection Slows Rift Phase –Coarse border, valley and lava rocks in normal faulted basins Drift Phase –Passive margin sediments Collision Phase –Subduction of ocean floor, island arcs form – Then collision

29. Crustal provinces: Proterozoic Tectonics Intensely folded rocks where cratons were sutured together in Early Proterozoic Slave Craton Rift and Drift Followed by Wopmay Orogen: remnants of old collisional mountains

30. Wilson Cycle 1&2 Rift & Drift Coronation Supergroup Proterozoic 2 bya as Slave craton pulled apart 2. Passive Margin sediments 1. Rift Valley Much later stuff

31. Near-collision phase of the Wilson Cycle in the Wopmay Orogen

32. 3. End of Wilson cycle in the Wopmay Orogeny Coronation Supergroup thrust faulted eastward over Slave Craton Note the vertical exaggeration

33. Key Events of Precambrian time

34. Proterozoic Assembly of Laurentia Trans-Hudson Orogen mostly 2.5 - 2 bya –Superior, Wyoming, Hearne plates sutured –Mountain range now eroded away Greenland, N. Gr. Brit., Scandinavia by 1.8 bya Continued accretion 1.8-1.6 bya of island arcs. Most of S. US “Mazatzal Province” Last piece “Grenville Orogeny” 1.3-1 bya Exposed Adirondacks and Blue Ridge Assembly of Rodinia by about 750 mya

35. Proterozoic Oxygen - Rich Atmosphere Eubacteria are photosynthetic 2 bya formed stromatolites along shores Free oxygen O 2 in atmosphere Band Iron Formations (common 3.8 – 2 bya) become rare, probably depended on disappearing conditions 2 bya Redbeds begin forming when iron in freshwater sediment is exposed to abundant atmosphere oxygen Oxygen in atmosphere irradiated - Ozone layer forms, protecting shallow water and land life forms from UV

36. Redbeds (also our campus)

37. Key Events of Precambrian time

38. Final Assembly of Rodinia Grenville Orogeny 1.3 – 1.0 BYA Eastern US Grenville collided with Grenville Craton, possibly west coast of S.America Southwest US collided w/ Antarctica –Grenville Orogeny continues in Antarctica South collided with Africa Rifted apart by 700 – 600 mya, about the Time of “Snowball Earth” at 635 mya

39. Growth of Laurentia Grenville: Shallow Water sandstones (lots of graywacke), mudstones and carbonates subjected to high-grade metamorphism and igneous intrusion

40. Grenville Collider was Western S. America?

41. Proterozoic Rifting Grenville Time Rifting 1.3 – 1 bya Kansas to Ontario to Ohio Rift Valley sediments and lavas 15 km (9 miles) thick! Rich in Copper, as are the rift valley sediments here. Why?

42. Midcontinent rift 1500 km long, exposed near L. Superior

43. Key Events of Precambrian time

44. Grenville Orogen Plenty of highlands, equator to poles What Plate Tectonic conditions favor glaciation?

45. Snowball Earth Rodinia: abundant basalts with easily weathered Ca feldspars. Ocean gets Ca + +. CO 2 tied up in extensive limestones. Less greenhouse effect. Atmosphere can’t trap heat – Earth gets colder Grenville Orogeny left extensive highlands –From high latitudes to equator About 635 mya glacial deposits found in low latitudes and elevations Huge Ice sheet reflects solar radiation “Albedo” Some workers believe oceans froze

46.  13C and  18O :3 - 4 Proterozoic Glaciations Earth surface became cold enough to produce glaciations and ice ages G - Glaciation BIF - Banded Iron Formation Snow-ball Earth Cambrian Stable isotopes of C and O

47. Break up of Rodinia Hypothesis: Ice an insulator, heat builds up Heavy volcanic activity poured CO 2 into atmosphere – greenhouse effect Warming melted snowball earth

48. Now, Precambrian Life Return to the Archean

49. Origin of Archean Life The origin of life required the organization of self-replicating organic molecules. The basic minimum requirements: –A membrane-enclosed capsule to contain the bioactive chemicals. –Energy-capturing chemical reactions capable of promoting other reactions. –Some chemical system for replication (RNA-DNA).

50. Formation of Enzymes 1950's and 1960's experiments produced amino acids by combining atmospheric gases, electrical sparks and heat. Further experiments demonstrated that drying and re- wetting of these organic compounds could produce cell-like membranes and simple proteins. –Led to shallow water “primordial soup” theory. –But organic compounds in shallow pools would have been instantly destroyed by ultraviolet radiation. Need an Oxygen-rich atmosphere to make an Ozone-Layer –Modern theory life started at deep sea vents near “Black smokers” –2 bya atmosphere has oxygen O2 –and ozone O3 which blocks UV Stanley L. Miller, working in the laboratory Stanley L. Miller, working in the laboratory of Harold C. Urey at the University of Chicago.

51. DNA => mRNA, TRNA aa bound to mRNA in Ribosomes Makes chain of amino acids (protein) The DNA sequence in genes is copied into a messenger RNA (mRNA). Ribosomes then read the information in this RNA and use it to produce proteins. Ribosomes do this by binding to a messenger RNA and using it as a template for the correct sequence of amino acids in a particular protein. The amino acids are attached to transfer RNA (tRNA) molecules, which enter one part of the ribosome and bind to the messenger RNA sequence. The attached amino acids are then joined together by another part of the ribosome. The ribosome moves along the mRNA, "reading" its sequence and producing a chain of amino acids. http://en.wikipedia.org/wiki/Archaea http://en.wikipedia.org/wiki/Ribosome

52. Key Events of Precambrian time Ca+ and CO 2 abundant during Rodinia Rifting Ended Snowball Earth

53. Origin of Life Origin of Archaebacteria 3.5 bya Archaebacteria are the most primitive fossil life forms –Likely ancestors of all life. Primitive Archaebacteria are hyperthermophiles that thrive near boiling point of water. –Modern Archaebacteria live in deep-sea volcanic vents. Some Archaebacteria feed directly on sulfur (chemoautotrophs). –Archean life probably arose in deep oceans hydrothermal environment; volcanic vents that would have formed near Mid- Ocean Ridges –Vents provide: chemical and heat energy, abundant chemical and mineral compounds, including sulfur deep water: protection from oxygen and ultraviolet radiation.

54. They differ from other bacteria (called Eubacteria) because: they are mostly anaerobic the RNA of their ribosomes is different from that of Eubacteria. They include the methane forming, the salt loving and the heat loving bacteria. Example: Methane Forming The methanogenic bacteria create Adenosine Tri Phosphate ATP by reducing carbon dioxide from the atmosphere using hydrogen, formate, or methanol. As a result methane is liberated. This can only be done in the absence of free oxygen.Adenosine Tri Phosphate ATPreducingcarbon dioxidehydrogenmethaneoxygen Archaebacteria CS: Define Eukaryote

55. Fossil Bacteria. About 2 bya Eubacteria ( prokaryotes lack membrane bound nucleus ) –Eubacteria form stromatolites (photosynthetic). –More common in upper Archean as shallow water shelves began to form along margins of early continents. –Archean is the age of pond-scum. Molds of individual bacterial cells found in Late Archean and Proterozoic cherts. 850 million years old Chroococcalean 0.85 bya Grypania 2.1 bya Palaeolyngbya 1. bya

56. 2 bya Photosynthesis Modern Stromatolites Shark Bay Australia Formed in areas where grazing gastropods can not thrive. Used to dominate the landscape in Pre-Cambrian and Early Cambrian. Also forming today on shores of Rift Valley Lakes in Kenya

57. Endosymbiosis – origin energy conversion plastids in Eukaryotes Energy transfer from sunlight Food oxidative reactions

58. Evolution of Eukaryotes Probably began as a endosymbiotic relationship between different prokaryotes. Early eukaryotes “ate” but could not digest a cell which became a mitochondria. oxidation Plant-like eukaryotic ancestors “ate” chloroplast-bearing cyanobacteria. photosynthesis Once eukaryotes evolved, multi-cellular forms proliferated.

59. Multi-cellular organisms appear in the Late Neoproterozoic (570 million years ago). Trace fossils (burrows, etc.) indicate motion of early multicellular forms. Ediacaran (Vendian 580-542 mya) fauna consist of simple organisms. Although originally believed to be related to Cnidarians or sponges, a closer look reveals they may represent several unknown early phyla. Idea: Early life forms had no competitors and were highly experimental in form? Evolution of Metazoans

60. Proterozoic Life First metazoans evolve 580-542 mya.First metazoans evolve 580-542 mya. Ediacara Fauna An arthropod? Jellyfish, Sea Pens? Not really.

61. Earliest hard parts Late Ediacaran to base of Cambrian http://en.wikipedia.org/wiki/Cloudinid

62. Next week, the Paleozoic