Some Major Events in the History of Life

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Some Major Events in the History of Life
Authors J.W. Schopf, A. Knoll, A. Nutman, J.
Kasting, J. Brocks. Chapters in book Bennett et
al Ch. 4 5
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Carbon Isotope Fractionation
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Stromatolites (3.6 Ga)
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Ancient Fossils
Bitter Springs (850 Ma)
Apex Chert (3.45 Ga)
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More evidence for early life Molecular Fossils

• What are molecular fossils (also called
  biomarkers)?
• molecules that are well-enough preserved (or
  whose degradation pathway and products are
  well-enough understood) that they can be used to
  indicate the presence of specific life forms in
  the rock record
• What molecules might be preserved in this way?
• Of the four major classes of large, complex,
  biomolecules,
• nucleic acids, proteins, lipids, and
  carbohydrates, some have potential as molecular
  fossils

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Nucleic acids (RNA, DNA)
hydrolyse rapidly
degrade quickly. In bones, collagen disintegrates
rapidly though small, compact proteins such as
osteocalcin may survive largely intact.
Proteins
Carbohydrates
Chitin? Cellulose? Not much work on these
?
Sterol lipids are often preserved well enough
that their original chemical form can be deduced
Lipids

• Some other important molecular fossils include
  porphyrins (chlorophyll, haem), sporopollenins,
  extremely resistant polymers that form the walls
  of pollen and spores and lignin, a complex
  polymer of phenolic alcohols found in vascular
  plant tissues. These are not easily categorized
  into these four groups
• The most abundant molecular fossil of all is
  kerogen insoluble, high-molecular weight organic
  matter of uncertain composition

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Carbon Cycle
CO2 (ATM) ? CO2 (Dissolved in Oceans) CO2
(Dissolved in Oceans) H2O ? HCO3- HCO3- Ca
? CaCO3 (Limestone)
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Oxygen Cycle
ferric iron oxides red beds
2.5 Ga
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Banded Iron Formations
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Billions of years ago
Banded Iron- Formations
Red Beds
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2
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Oldest known microfossils
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OXYGEN AND CARBON DIOXIDE IN THE EARTHS
ATMOSPHERE DURING ITS FIRST 4 BILLION YEARS
present level (21)
1.0
Oxygen
CARBON DIOXIDE
0.1
0.01
OXYGEN
0.0001
present level (0.037)
Carbon Dioxide
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3
2
1
0
Billions of years ago
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Ancient molecular fossils Brocks et al. 1999
Iron oxide layers givethis rock its reddish hue
2.6-2.8 billion year old rocks in the Hamersley
Range, Australia, where Brocks et al. 1999 found
cyanobacterial biomarkers. This supports the
hypothesis that photosynthesis provided the
oxidizing power to precipitate the Hamersley iron
formation.
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Acritarchs
1.9 Ga
The Rise of Oxygen allows the development of more
complicated organisms
Why??
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Sepkoski Curves
Studying variation in the fossil record allows
you to spot extinction events