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PRECAMBRIAN PROTEROZOIC
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t08_03_pg226 PRECAMBRIAN EONS PROTEROZOIC EON ARCHEAN EON HADEAN EON
t08_03_pg226.jpg ARCHEAN EON HADEAN EON t08_03_pg226
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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
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Proterozoic
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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
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(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)
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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
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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
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Proterozoic Era Highlights
Neoproterozoic (1.0 GA to 542 MA) Extreme Glaciation (Snowball Earth) Earliest Multicellular Organisms (Ediacaren) Break-up of Rodinia Supercontinent
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Supercontinents
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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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Oxygen Catastrophy
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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.
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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).
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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.
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Asteroid Impacts
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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
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Glacial Episodes
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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.
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Glaciation Snowball Earth (635 – 750 MA) Marinoan (635 – 700 MA)
Sturtian (700 – 750 MA) Huronian (2.5 – 1.6 GA)
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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
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ICE THICKNESSES
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Proterozoic Life Forms
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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
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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
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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)
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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
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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
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Proterozoic Life Forms
Another big change in the Proterozoic was the appearance of the first Metazoans 5 cm
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Proterozoic Life Forms
They are known as the Ediacarin Fauna And they are found around the world
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Proterozoic Life Forms
What were the Ediacarins? Three major “forms”
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Proterozoic Life Forms
Whatever they were, they “exploded” onto the scene immediately after the last Snowball Earth.
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Proterozoic Life Forms
What happened to them? 1) a now extinct line of beasties 2) ancestors to living phyla Kimberella sp.
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Evidence of Proterozoic Life
Direct Evidence Fossils Trace Fossils
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Evidence of Proterozoic Life
Indirect Evidence BIFs (Banded Iron Formation)
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Factors Affecting Development of Proterozoic Life
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Proterozoic Fossils Severe environmental changes drives evolutionary adaptation. We need bad things to happen in order to evolve.
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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)
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Factors Affecting Development of Proterozoic Life
“Atmospheric Changes”
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Factors Affecting Development of Proterozoic Life
“Atmospheric Changes”
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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)
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Factors Affecting Development of Proterozoic Life
Extra-Terrestrial Solar Radiation Impact Events
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Implications of Proterozoic Info
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Implications of Proterozoic Info
Ediacarin Evolutionary Development Diversity of Life Present Day Global Warming
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THE END
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