1. First Life….. 1) Proterozoic Eon = before animals
**Before animals there were
many types of
unicellular organisms
single celled living things
2) Phanerozoic Eon =
Multicellular animals appear

2. 1st living thing =Bacteria
3.4 byo, South Africa
1) Prokaryotic=
before nucleus
2) Heterotrophic:
eat food(not photosynthetic)
3) anaerobic:
live without O2
4) fermenters:
use organic molecules for chemical energy
waste = alcohol + CO2
modern

3. 2nd living things Archaebacteria
extremohiles
oldest still living life forms
very similar to earliest life forms
live in “extreme” environments
1) Anaerobic environments
2) Extreme high temperature
(thermophiles)
3) Extreme high salt
(halophiles)

4. Hot Springs Conditions very like Archean Earth High Temperatures
Low free oxygen
Archeabacteria live here today

5. Deep Ocean boiling water from vents through crust
very stable environment
Lots of clay for concentration
very protected
lots of minerals
warm -> hot
Archaebacteria

6. The First Energy Crunch Produced the Third Type of Living Thing
organic molecules in primordial soup run low
competitive advantage goes to….
organisms that can make their own food
crisis solved for some by origin of _____________
Photosynthesis

7. Cyanobacteria Photosynthetic bacteria – give off O2
Early cyanobacteria were anaerobic so,
the O2 they made was toxic to them
When their O2 waste product built up..
they died

8. What Likely Happened
O2 made by anaerobic cyanobacteria at ocean’s surface
O2 toxic to them in high concentrations
but not if the O2 was removed from the water by bonding with iron (Fe)
Oceans contained dissolved iron eroded from the land

9. Banded Iron Formations Created
iron easily dissolved in anaerobic water
when iron bonds to O2 it becomes a solid
the solid sinks to the ocean floor and is deposited in layers
Layers of oxidized iron are red

10. Dark, Unoxidized Bands Form
When all of the dissolved Fe is removed from the water, O2 builds up
High O2 concentrations kill the cyanobacteria
Dark sediments are deposited that have no oxidized iron in them

11. Why are BIFs Banded? When runoff added more Fe to the water the entire process stared over again.

12. Banded Iron Formations
Indirect (non-fossil) evidence
for the presence of
cyanobacteria ~ 3.5 bya

13. BIFs (Banded Iron Formations)
thick (100s of feet) deposits
consist of layers of iron-rich rock interbedded with iron-poor chert
Precambrian,
Australia

14. BIFs began forming about 3.5 bya = 1st free O2
reached peak about 2.5 bya
deposition ended about 1.8 bya

15. Oxygen Crisis eventually, oxygen built up in oceans
then outgassed from oceans into the atmosphere
corrosive (oxic) atmosphere led to first major mass extinction
anaerobic bacteria restricted to refuges without abundant oxygen (stagnant water, deep soils, etc.)

16. Red Beds sedimentary rocks that are very red
form above the surface of the water
iron minerals in the sediment “rust”
indicate continuous presence of free oxygen in the atmosphere

17. Aerobic Bacteria some bacteria evolved antioxidant mechanisms
allowed those bacteria to tolerate rising O2 levels
some bacteria even evolved to use O2

18. How Far Back Does the Fossil Record Extend?

19. Bacterial fossils preserved in the act of division.
2.1 Billion years old, Hudson Bay, Canada
~3.4 billion years old, South Africa
modern bacteria in similar stages of division

20. Almost Certainly
900 myo - Australia
Bitter Springs Formation

21. Likely
byo - South Africa
Fig Tree Group

22. 3.5 byo - Australia Maybe? Modern cyanobacteria for comparison
Warrawoona Group, Australia

23. Living
Precambrian
Cyanobacteria
Ancient vs. Modern

24. Why Do We Care Again? build-up of free oxygen started ~ 3.5 bya
argues for evolution of photosynthetic life by that time
living organisms completely altered the face of the planet

25. Earliest (Undisputed) Evidence of Life - Stromatolites
2.2 byo Michigan

26. Stromatolites dome-shaped, layered structures may be as old as 3.5 byo
became very abundant by 2.2 bya
consist of layers of bacteria
upper layers aerobic, photosynthetic
lower layers anaerobic
produce abundant oxygen
how do we know?

27. They are still alive today in special environments, notably Shark Bay, Australia
Tide In
Tide Out

28. Formation of Stromatolites
Cyanobacteria form a mat
on top of sediment
A new layer of sediment
is deposited on top
1 cm
Bacteria grow up
through new layer

30. Stromatolites provide evidence for the
occurrence of cyanobacteria in the fossil record.
Modern
Ancient

31. if we use stromatolites to infer the presence of cyanobacteria
we might expect to find fossils of bacteria-like organisms in them...

32. Gunflint Chert (~2.0 billion years old), Canada
And we often find them . . .
Gunflint Chert (~2.0 billion years old), Canada

34. How Does It All Add Up?

35. O2
added
O2 in
Atmos.

36. Domains of Living Things
(All living things divided into 3 Domains)
Oldest domain =
Domain Bacteria
2nd Oldest domain =
Domain Archaea
Most modern domain=
Domain Eukarya

37. Order of Appearance of Life Forms
First =
heterotrophic/anaerobic bacteria
Second =
heterotrophic/anaerobic Archaebacteria
Third =
photosynthetic cyanobacteria
Fourth =
Aerobic Eukaryotes

38. The rise of cyanobacteria and the building up of oxygen in the Earth’s atmosphere had three significant effects:
life forever changed the surface of the Earth
Earth experienced the first mass extinction
an oxygen-rich atmosphere set the stage for the appearance of complex life