Earth History
GEOL 2110
Early Life
Chapter 9
Major Concepts
• The oldest fossils known are filaments of cyanobacteria
(blue-green algae) that are 3.5 billions years old
• Experiments simulating the origins of life are able to
create the building blocks of life (proteins and amino
acids) from the primordial soup of the early earth oceans
and oxygen-depleted atmosphere.
• Simple, asexually reproducing, single-celled organisms
persisted until 700 million years ago.
• The first multicellular organism appeared as soft-bodied
creatures around 700 million years ago during a period of
extensive global glaciation, supercontinent breakup, and
carbon infusion into the oceans
• The appearance of organisms with skeletons appeared in
the Cambrian after a significant increase in oxygen
•Conditions on Earth 3.5-4.0 Ga
Oxygen deficient (anaerobic) atmosphere
Late Heavy Bombardment (4.1-3.8 Ga)
Oceans present since 4.2 Ga (very warm)
Darwin’s “Warm Little Pond” - Primordial
Soup (CH4, NH3, CO2, N2 rich) – all the
components necessary to make life
Intense UV bombardment (no ozone)
Origin of Life: Early Ideas
• Spontaneous
Generation –
process of
putrefaction
somehow producing
metamorphosis of
nonliving to living
matter
• Louis Pasteur's
sealed flask
If life doesn't spontaneously generate
experiments
now, how could it in the past?
Recreating the “Warm Little Pond”
Miller demonstrated that a wide
range of vital organic compounds
(amino acids, cyanide,
formaldehyde) can be synthesized
by fairly simple chemical processes
from inorganic substances
Stanley Miller
1930- 2007
Making Polymers
Sidney Fox
1912-1998
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)
Protenoids behave much like bacteria, regulate
their cells, excrete waste, metabolize sugars
Cell membranes
Formed from fatty acids carboxyl group (COOH)
and aliphatic chain
Fatty acid (hydrophobic) +
alcohol (hydrophyllic)
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
Reproduction
Coding and Replication
Which came first?
Protein synthesis or
nucleic acid (RNA)
Current thinking is RNA
evolved first as “naked
genes” and become
encoded with the help
of ribozymes
Other Templates suggested for serving as templates for
reproduction are: Clays, Zeolites, and Pyrite (FeS2)
Single-celled Prokaryotes Rule
3,500 – 700 Ma
3.5 Ga
Cyanobacteria
Australia
1.15 Ga
4-celled
cyanobacteria
in chert
Modern
filamentous
cyanobacteria,
Lyngbya
3.4 Ga
stromatolite
Swaziland
Supergroup,
South Africa
Evolution of Prokaryotes and Eukaryotes
Reducing, sulfur-rich
Hydrothermal vents
Photosynthesizing
bacteria
Fig. 9.7
Prokaryotes and Eukaryotes
Evolution of Eukaryotes
More complex eukaryotes are
thought to have developed
from symbiotic relationships
between prokaryotes
Symbiotic origin of Eukaryotes
around 1.75 Ga, didn't
diversify much until 1.1 Ga
(sexual reproduction?)
Multicellullar Organism (Metazoans)
Appear ~ 600Ma
Ediacaran Metazoan Trace Fossils
Metazoan fossils from Ediacara Hills,
Australia, 600 to 550 million years ago.
Soft bodied - like jelly fish or sea pens
Cambrian Explosion (535--510 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 of Rodinia
Additional contributors to the
Cambrian Explosion
Potentially higher atmospheric O2 (close to
modern concentrations) promotes calcite
exoskeleton secretion (phosphate and silica
common under low O2 conditions).
Increased nutrients associated with more rifting
and volcanic activity
Abundant cyanobacterial mats for molluscs and
other small invertebrates to graze
Development of predators
Tiering of biotic activity on the sea floors
Burgess Shale
Middle Cambrian from Field, British Columbia (discovered
in 1909)
Abundant well preserved fossils of soft bodied animals
Highly experimental forms
Summary of Early Earth Events
Next Lecture
Vendian, Cambrian and Early Ordovician Periods
Part I
Chapter 10