THE PRIMORDIAL EARTH

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THE PRIMORDIAL EARTH Hadean and Archean
Eons Evidence of Anoxia
Lack of oxidized iron in the oldest sedimentary
rocks. Urananite and pyrite are readily oxidized
today, but are found unoxidized in Precambrian
sediments Archean sedimentary rocks are
commonly dark due to the presence of carbon,
which would have been oxidized if oxygen had
been present.
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Evidence of Anoxia
Archean sedimentary sequences lack carbonate
rocks but contain abundant chert, presumably
due to the presence of an acidic, carbon
dioxide-rich atmosphere. Carbon dioxide and
water combine to form carbonic acid. In such
an acidic environment, alkaline rocks such as
limestone do not develop.
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Evidence of Anoxia
Banded iron formations (BIF) appear in
stratigraphic record in the Precambrian (1.8 -
about 3 by).
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Evidence of Anoxia
Banded iron formations (BIF) appear in
stratigraphic record in the Precambrian (1.8 -
about 3 by). They are cherts with alternating
laminations of red oxidized iron and gray
unoxidized iron. Origin of these BIFs is
puzzling, and several possible explanations
exist. May be related to hydrothermal vents
(hot springs) in the sea floor.
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Evidence of Anoxia
Bacteria may have played a role in the origin of
BIFs. The simplest living organisms have an
anaerobic metabolism. They are killed by
oxygen. Includes some bacteria (such as
botulism). Includes some or all Archaea, which
inhabit unusual conditions Chemical building
blocks of life could not have formed in the
presence of O2 (amino acids, DNA)
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Evolution of the Hydrosphere
Ocean Formation - As the Earth cooled, H2O
produced by out gassing could exist as liquid
in the Early Archean, allowing oceans to form.
Evidence - pillow basalts, deep marine sediments
in greenstone belts.
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Evolution of the Hydrosphere
Oceans were originally freshwater (rain) may
have been acidic from carbon dioxide and
sulfurous gases in the atmosphere. Slow
accumulation of salts derived from weathering
(dissolution of soluble minerals). Ocean
salinity is relatively constant today because
surplus salts are precipitated at about the
same rate at which they are supplied to the sea.
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Evolution of the Hydrosphere
Sodium remains in sea water due to its high
solubility. Today Earth's water is continuously
re-circulated through the hydrologic cycle
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Formation of Atmosphere with Oxygen
The development of an oxygen-rich atmosphere is
the result of 1. Photochemical dissociation -
breaking up of water molecules into hydrogen
and oxygen in the upper atmosphere caused by
ultraviolet radiation from the sun (minor
process) 2. Photosynthesis - the process by
which plants produce oxygen (major process)
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Evidence of Free Oxygen
Red sediments with iron oxide (red beds) appear
in the stratigraphic record after the last
appearance of the BIF (younger than 1.8 by).
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Evidence of Free Oxygen
Carbonate rocks (limestones and dolostones)
appear in the stratigraphic record at about the
same time that red beds appear.
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Archean Rock Types

• Granulites
• Highly metamorphosed gneisses (metamorphosed
• tonalites, granodiorites, and granites) and
• anorthosites (layered intrusive gabbroic rocks)

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THE PRIMORDIAL EARTH Hadean and Archean
Eons Archean Rock Types
Greenstones Low-grade metamorphic minerals
chlorite and hornblende produce green color.
Mostly in trough-like or synclinal belts.
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Archean Rock Types

• Volcanics
• Volcanic (basaltic, andesitic, and rhyolitic)
  rocks
• with pillow structures (pillow basalts),
  indicating
• extrusion under water.

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THE PRIMORDIAL EARTH Hadean and Archean
Eons Archean Rock Types
Meta-sedimentary rocks Metamorphosed sedimentary
rocks derived from the weathering and erosion
of the volcanics. Metagraywackes, slates,
schists, metaconglomerates (with granite
pebbles), diamictites. Mostly deep water
deposits.
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Archean Life
The earliest evidence of life occurs in Archean
sedimentary rocks.
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Archean Life
Oldest direct evidence of life is in 3.5 by old
Chert bed associated with Warrawoona
Group western Australia
Similar to cyanobacteria living today, which
produce O2.
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Archean Life

• Stromatolites (cyanobacteria - blue-green
  algae)Also in rocks 2.8 - 3 by old - Pongola
  Group of southern
• Africa, and Bulawayan Group of Australia. More
  abundant later in Proterozoic rocks, but they are
  rare
• today.

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THE PRIMORDIAL EARTH Hadean and Archean
Eons Archean Life
Algal filament fossils (filamentous
prokaryotes)3.5 b.y. at North Pole, western
Australia
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Archean Life
Spheroidal bacterial structures (Monera)Fig Tree
Group, South Africa 3.0 - 3.1 by cherts, slates,
ironstones, and sandstones prokaryotic cells,
showing possible cell division
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THE PRIMORDIAL EARTH Hadean and Archean Eons The
Origin of Life
Most likely developed under anaerobic
conditions O2 is poisonous to the construction
of organic molecules No O3 layer to serve as
protection from ultraviolet radiation
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THE PRIMORDIAL EARTH Hadean and Archean Eons The
Origin of Life
Consequently life may have developed in water at
depth below the surface of rocks
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THE PRIMORDIAL EARTH Hadean and Archean Eons The
Origin of Life
Consequently life may have developed in the
vicinity of black smokers (deep sea hydrothermal
vents)
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THE PRIMORDIAL EARTH Hadean and Archean Eons The
Origin of Life
Elements necessary to produce life Carbon
Hydrogen Oxygen Nitrogen Phosphorus Sulfur
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THE PRIMORDIAL EARTH Hadean and Archean Eons The
Origin of Life
Four essential components of life Proteins
(chains of amino acids linked together), used
to build living materials and as catalysts in
chemical reactions in organisms. Nucleic acids
DNA RNA Organic phosphorus, used to
transform light or chemical fuel into energy
required for cell activities. A cell membrane to
enclose the components within the cell.
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THE PRIMORDIAL EARTH Hadean and Archean Eons The
Origin of Amino Acids
Lab experiments by Miller and Urey in the
1950'sFormed amino acids fromH2 CH4
(methane) NH3 (ammonia) H2O (steam) and sparks
(to simulate lightning)
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Making Proteins
Amino acids join together to make proteins. For
them to join it requires Input of energy
Removal of water
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Making Proteins
Where do we get the energy and remove
water? Heating from volcanic activity At lower
temperatures in the presence of phosphoric acid.
Evaporation Freezing Involve water in a
dehydration chemical reaction On clays, which
have charged surfaces, and to which polar
molecules could attach On pyrite, which has a
positively charged surface to which simple
organic compounds can become bonded. Formation
of pyrite yields energy which could be used to
link amino acids into proteins
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THE PRIMORDIAL EARTH Hadean and Archean
Eons Making Proteins
Proteinoids produced experimentally Film-like
outer wall Capable of osmotic shrinking and
swelling Budding similar to yeast Divide into
daughter microspheres Aggregate into lines to
form filaments, as in some bacteria Streaming
movement of internal particles, as in living
cells