Transcript Early Life and its Patterns

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Evolution of the
Earth
Seventh Edition
Prothero • Dott
Chapter 9
Early Life and its Patterns
• Origin of Life – early work and controversies,
potential mechanisms for abiogenesis
• Record of early life- what do they tell us about
Earth at the time? The major players?
• Cambrian explosion - Earth's effect on life,
life's effect on Earth
Origin of Life: Early Ideas
• Spontaneous
Generation –
process of
putrefaction
somehow
producing
metamorphosis of
nonliving to living
matter
• Louis Pasteur's
sealed flask
experiments
•If life doesn't spontaneously generate now, how
could it in the past?
- Conditions on Earth were different 3.5-4.0
bya
– Composition of the atmosphere (reducing vs
oxidizing), forms of nutrients, conditions of the
oceans, temperatures etc. Life radically
changed the Earth.
– “Warm Little Pond” - Primordial Soup (CH4,
NH3, CO2, N2 rich)
– Intense UV bombardment (no ozone)
– Late Heavy Bombardment (4.1-3.8 bya)
Fig. 9.2 (Atm of
H2, CH4, NH3)
What about polymers? Simplest cells
have more complex organic molecules
• Polymer – complex chains of linked simple
organic molecules (proteins, nucleic acids,
sugars, fats, enzymes)
• Experimentally derived in a number of ways
• – splashing amino acids under hot, dry conditions
forming proteins (Sidney Fox)
– Cyanide, clays, and heat capable of
polymerizing amino acids into proteins
– Can form nucleotides under similar conditions
(heating of ammonium and cyanide – Miller)
Cell membranes?
• Formed from fatty acids - carboxyl group
(COOH) and aliphatic chain
• Fatty acid + alcohol form lipids
• Lipids form cell membranes that regulate
what goes in an out of a cell
• Actually easy to synthesize as well as
found on meteorites
• Chicken or Egg – RNA vs Proteins?
Fig. 9.4 Lipid
Bilayer
Fig. 9.5
Protenoids:
behave much like
bacteria, regulate
their cells, excrete
waste, metabolize
sugars
Fig. 9.1 (3.6 bya)
What about the rock record?
Fig. 9.6 Thermophiles, chemosynthetic, hydrothermal vents vs cyanobacteria (both
prokaryotes)
Fig. 9.7
Fig. 9.8f
3.4 by stromatolite
– Swaziland
Supergroup, South
Africa
Fig. 9.8g, Modern
filamentous
cyanobacteria,
Lyngbya – cells are
identical to those of
Warrawoona Group
Fig. 9.8h – 4 celled
cyanobacteria 1.55
bya
Fig. 9.8i
Modern colonial
cyanobacteria,
Gloecapsa
Fig. 9.10 – More
complex eukaryotes
developing from
symbiotic
relationships
between
prokaryotes
- Symbiotic origin
of Eukaryotes
around 1.75 ba,
didn't diversify
much until 1.1 bya
(sexual
reproduction?)
Fig. 9.11abc
Ediacaran metazoan
trace fossils (635542 ma)
Why don't we find more PreCambrian fossils?
• Most transitions between pre-Cambrian
rocks and Cambrian have a profound
unconformity, many pre-Cambrian rocks
are metamorphosed
• Most Ediacaran metazoans are soft bodied
animals (hard to preserve)
Cambrian Explosion (540 ma)
• Soft bodied organisms replaced with many
fossils of shelled invertebrates
• Significant amounts of burrowing/trace
fossils
• Large diversification of fossil record
• Likely related to the end of the extreme
Varangian glaciation and increased tectonic
rifting
Fig. 9.13 Early Cambrian shelled fossils thought to
be related to sponges, corals, or molluscs
Fig. 9.14
Additional contributors to the Cambrian Explosion
• Potentially higher atmospheric O2 (size of
metazoans)
• Increased nutrients associated with more rifting
and volcanic activity
• Calcite secretion; phosphate and silica
exoskeletons easier to synthesize under low atm.
O2
• Abundant cyanobacterial mats for molluscs and
other small invertebrates to graze
• Development of predators
• Tiering of biotic activity on the sea floors
Fig. 9.15
Fig. 9.16a
Ollenellus
Free tail spines
Fig. 9.16b
Ogygopsis
tail spines fused
into single plates
Fig. 9.16c
Paradoxides
Fig. 9.16d
Elrathia
Juveniles to adults
Fig. 9.16e
agnostids, blind
trilobites,
possibly floated
Fig. 9.17
Fig. 9.19
Helioplacus
“experimental”
echinoderm
Burgess Shale
• Middle Cambrian from Field, British
Columbia (discovered in 1909)
• Abundant fossils of soft bodied animals,
highly preserved
• Provides a rare glimpse at the diversity of
soft-bodied organisms that are rarely
preserved
• Highly experimental forms
Fig. 9.22a
Fig. 9.22b