1. PRECAMBRIAN
PROTEROZOIC

2. t08_03_pg226 PRECAMBRIAN EONS PROTEROZOIC EON ARCHEAN EON HADEAN EON
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ARCHEAN EON
HADEAN EON
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4. Defining Characteristics of 3 Eons
Hadean: 4.6–4.0 bya
formation of Earth’s crust and main bombardment
Archean: 4.0–2.5 bya
first life appears
plate tectonics established
oxygen-poor atmosphere
Proterozoic: 2.5 bya–542 mya
first multicellular animals at end of interval
4 major mountain-building episodes
oldest known glaciation

5. Proterozoic

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7. Key Events 2 Supercontinent Episodes
3 Glacial Episodes (Snowball Earth)
Change from O2 Poor to O2 Rich
2 Major Meteor Impacts
BIFs (Major Source of Iron)
Major Copper Deposits
Evolution of Life from One Cell to Multi-Cell

8. (542 MA to 2.5 GA: ~ 2 Billion years old)
Background Info
Proterozoic is the largest Eon
(542 MA to 2.5 GA: ~ 2 Billion years old)
Consists of 3 Eras - Each is as large or larger than the entire Phanerozoic Eon.
Neoproterozoic (542 MA to 1.0 GA)
Mesoproterozoic (1.0 GA to 1.6 GA)
Paleoproterozoic (1.6 GA to 2.5 GA)

9. Proterozoic Era Highlights
Paleoproterozoic (2.5 GA to 1.6 GA )
Evolution of Cyanobacteria (O2 Producers)
O2 Catastrophy
BIFs (Banded Iron Formations)
Huronian Glaciation
2 Largest Impact Events in Earth’s History
South Africa – Vredefort
Ontario Canada – Sudbury Basin
Earth’s Atmosphere Changed to an O2 Environment
Columbia Supercontinent Formed

10. Proterozoic Era Highlights
Mesoproterozoic (1.6 GA to 1.0 GA)
Red Algae
First Sexual Reproduction
Earliest Complex Multicellular Organism
Columbia Supercontinent Broken up
Rodinia Supercontinent Formed

11. Proterozoic Era Highlights
Neoproterozoic (1.0 GA to 542 MA)
Extreme Glaciation (Snowball Earth)
Earliest Multicellular Organisms (Ediacaren)
Break-up of Rodinia Supercontinent

12. Supercontinents

13. Plate Tectonics Wilson Cycle (3 Parts) Supercontinent Episodes
Opening of an Ocean Basin
Sedimentation
Closing of an Ocean Basin
Supercontinent Episodes
Rodinia: 1.6 to 1.0 bya
Columbia (Laurentia): 2.5 to 1.6 bya
Orogenic Episodes
Wopmay (Laurentia)
Keeweenewan (Laurentia)
Greenville (Rodinia)

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15. Oxygen Catastrophy

16. Oxygen Catastrophy (1.6 – 2.5 bya)
Oxygen created from photosynthesis
Oxygen toxic to anaerobic organisms
Initial lag of 300 million years for free oxygen in the atmosphere
Oxygen initially combined with free iron in the oceans to form magnetite.

17. Formation of an Oxygen-rich Atmosphere
The change from an oxygen-poor to an oxygen-rich atmosphere occurred by the Proterozoic, which began 2.5 billion years ago at the end of the Archean.
The development of an oxygen-rich atmosphere is the result of:
Photochemical dissociation - The breaking up of water molecules into hydrogen and oxygen in the upper atmosphere caused by ultraviolet radiation from the Sun (a minor process today)
Photosynthesis - The process by which photosynthetic bacteria and plants produce oxygen (major process).

18. Evidence for Free Oxygen in the Proterozoic Atmosphere
Red beds, or sedimentary rocks with iron oxide cements, including shales, siltstones, and sandstones, appear in rocks younger than 1.8 billion years old. This is in the Proterozoic Eon, after the disappearance of the BIF.
Carbonate rocks (limestones and dolostones) appear in the stratigraphic record at about the same time that red beds appear. This indicates that carbon dioxide was less abundant in the atmosphere and oceans so that the water was no longer acidic.

19. Asteroid Impacts

20. Asteroid Impacts Paleoproterozoic (2.5 GA to 1.6 GA ) U.S.:
2 Largest Impact Events in Earth’s History
South Africa – Vredefort
Ontario Canada – Sudbury Basin
U.S.:
Barringer Meteor Crater - Arizona

21. Glacial Episodes

22. Glaciation
By 2.8 billion years ago, Earth had cooled sufficiently for glaciation to occur. Earth's earliest glaciation is recorded in 2.8 billion year-old sedimentary rocks in South Africa.

23. Glaciation Snowball Earth (635 – 750 MA) Marinoan (635 – 700 MA)
Sturtian (700 – 750 MA)
Huronian (2.5 – 1.6 GA)

24. Snowball Earth (630 – 850 mya)
Glacial Periods: Startian & Marinoan/Varanger
Causes
Reflective surface of continents
Removal of CO2 from atmosphere
Change in ocean circulation patterns
Intro of pure oxygen which converted methane into CO2
Reduction in Organic Activity
Subsequent melting caused by emission of CO2 from volcanic activity

25. ICE THICKNESSES

26. Origin of Life

27. Archian Life Forms

28. Life of the Archean - The Fossil Record
The earliest evidence of life occurs in Archean sedimentary rocks.
Evidence of Archean life consists of:
Stromatolites - An organo-sedimentary structure built by photosynthetic cyanobacteria or blue-green algae. They are not true fossils.
Stromatolites form through the activity of cyanobacteria in the tidal zone. The sticky, mucilage-like algal filaments of the cyanobacteria trap carbonate sediment during high tides. Modern stromatolites are found today in isolated environments with high salinity, such as Shark Bay, western Australia.

29. Other evidence of Archean life:
Oldest direct evidence of life Microscopic cells and filaments of prokaryotes. Found in Warrawoona Group, Pilbara Supergroup, western Australia b.y.
Indirect evidence of life in older rocks Found in banded iron deposits in Greenland. Carbon-13 to carbon-14 ratios are similar to those in present-day organisms. 3.8 b.y.
Algal filament fossils Filamentous prokaryotes preserved in stromatolites. Found at North Pole, western Australia b.y.
Spheroidal bacterial structures Found in rocks of the Fig Tree Group, South Africa (cherts, slates, ironstones, and sandstones). Prokaryotic cells, showing possible cell division b.y.
Molecular fossils Preserved organic molecules that only eukaryotic cells produce. Indirect evidence for eukaryotes. In black shales from northwestern Australia. 2.7 b.y. Origin of eukaryotic life is pushed back to 2.7 b.y.

30. The Origin of Life Creation of amino acids
UV radiation can recombine atoms in mixtures of water, ammonia and hydrocarbons, to form amino acids. (The energy in lightning can do the same thing.)
Lab simulation experiments by Miller and Urey in the 1950's. Formed amino acids from gases present in Earth's early atmosphere: H2, CH4 (methane), NH3 (ammonia), and H2O (water vapor or steam), along with electrical sparks (to simulate lightning).

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Miller and Urey
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32. Where Did Life Originate?
Early life may have avoided UV radiation by living:
Deep beneath the water
Beneath the surface of rocks (or below sediment - such as stromatolites)
Life probably began in the sea, perhaps in areas associated with submarine hydrothermal vents or black smokers.
Evidence for life beginning in the sea near hydrothermal vents:

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34. Evolution of early life and the transition from prokaryotes to eukaryotes
The earliest cells had to form and exist in anoxic conditions (in the absence of free oxygen).
Likely to have been anaerobic bacteria or Archaea.
Some of the early organisms became photosynthetic, possibly due to a shortage of raw materials for energy.
Photosynthesis was an adaptive advantage.
Oxygen was a WASTE PRODUCT of photosynthesis.
Consequences of oxygen buildup in the atmosphere:
Development of ozone layer which absorbs harmful UV radiation, and protected primitive and vulnerable life forms.
End of banded iron formations which only formed in low, fluctuating O2 conditions
Oxidation of iron, leading to the beginning of red beds - iron oxides (hematite).

35. Proterozoic Life Forms

36. Proterozoic Life Forms
Acritiarchs (Single Celled)
Ediacarens (Multi-Celled)
Evolutionary Development
From Prokaryotic to Eukaryotic
Onset of Sexual Reproduction
From Single Cell to Multi-Cell
Soft-Bodied to Shell Covering

37. Evolution of early life and the transition from prokaryotes to eukaryotes
No Nucleus or organelles
reproduce asexually by simple cell division. This restricts their genetic variability. For this reason, prokaryotes have shown little evolutionary change for more than 2 billion years.
Eukaryotes
contain a nucleus and organelles
Aerobic metabolism developed. Uses oxygen to convert food into energy.
could cope with the oxygen in the atmosphere.
reproduce sexually leading to genetic recombination and increased variability and rate of evolution.
Origin of eukaryotic life was probably around 2.7 b.y., based on molecular fossils.
appeared in the fossil record about billion years ago (in the Proterozoic).
Eukaryotes diversified around the time that the banded iron formations disappeared and the red beds appeared, indicating the presence of oxygen in the atmosphere.

38. Proterozoic Life Forms
During the Archean, we saw the rise of the prokaryotes:
Small
No nucleus
DNA spread throughout the cell
Asexual reproduction
Could only be single-celled

39. Proterozoic Life Forms
During the Proterozoic:
the rise of EUKARYOTES:
Larger (>0.06 mm)
A nucleus and organelles
DNA contained within the nucleus
Sexual reproduction
Could be multi-celled (metazoans)

40. Endosymbiotic Theory
The Endosymbiotic Theory for the Origin of Eukaryotes proposes that billions of years ago, several prokaryotic cells came together to live symbiotically within a host cell as protection from (and adaptation to) an oxygenated environment. These prokaryotes became organelles. Evidence for this includes the fact that mitochondria contain their own DNA. Example - a host cell (fermentative anaerobe) + aerobic organelle (mitochondrion) + spirochaete-like organelle (flagellum for motility).

41. Proterozoic Life Forms
The first eukaryotes appeared around 2 GA. Archritarchs were small, single celled silica beasties that floated in the oceans (pelagic). They peaked in abundance at 750 MA and then went away…
0.1mm

42. Proterozoic Life Forms
… or did they? They might in fact be ancestors to equally small single celled organisms that are around today called dinoflaggelates.
0.1mm

43. Proterozoic Life Forms
Another big change in the Proterozoic was the appearance of the first Metazoans
5 cm

44. Proterozoic Life Forms
They are known as the Ediacarin Fauna
And they are found around the world

45. Proterozoic Life Forms
What were the Ediacarins?
Three major “forms”

46. Proterozoic Life Forms
Whatever they were, they “exploded” onto the scene immediately after the last Snowball Earth.

47. Proterozoic Life Forms
What happened to them?
1) a now extinct line of beasties
2) ancestors to living phyla
Kimberella sp.

48. Evidence of Proterozoic Life
Direct Evidence
Fossils
Trace Fossils

49. Evidence of Proterozoic Life
Indirect Evidence
BIFs (Banded Iron Formation)

50. Factors Affecting Development of Proterozoic Life

51. Proterozoic Fossils
Severe environmental changes drives evolutionary adaptation.
We need bad things to happen in order to evolve.

52. Factors Affecting Development of Proterozoic Life
Terrestrial
Atmospheric Changes
Climate
Geography
Results
Greenhouse Earth (no continental glaciers present)
Icehouse Earth (continental glaciers present)
Snowball Earth (Frozen oceans at equator)

53. Factors Affecting Development of Proterozoic Life
“Atmospheric Changes”

54. Factors Affecting Development of Proterozoic Life
“Atmospheric Changes”

55. Factors Affecting Development of Proterozoic Life
“Climatic Changes”
We now recognize three major Earth phases
1) Greenhouse Earth
(no continental glaciers present)
2) Icehouse Earth
(continental glaciers present)
3) Snowball Earth
(Frozen oceans at equator)

56. Factors Affecting Development of Proterozoic Life
Extra-Terrestrial
Solar Radiation
Impact Events

57. Implications of Proterozoic Info

58. Implications of Proterozoic Info
Ediacarin Evolutionary Development
Diversity of Life
Present Day Global Warming

59. THE END