1. Earth History

2. Eons – largest time division
Eons determined by major changes in the Earth
Most recent Eon started with the appearance of multicellular animals = Phanerozoic Eon
Three Eons make up what was previously know as the Precambrian Period
1) Proterozoic
2) Archean
3) Hadean

3. 1. The Hadean Eon: 4.6 to 3.8 billion years ago
Earth & other planets formed from dust and gasses surrounding the sun

4. Gravity gathers dust into large lumps, called planetisimals
Collisions between lumps makes lots of heat
The Earth was molten during the Hadeon Eon.
Steam atmosphere formed from light elements

5. Heavy elements in the planets suggest the dust/gas came from a supernova
We can observe other solar systems forming today
They form in diffuse nebulae like nebula M16.

6. After most planetisimals had become part of a planet, there were fewer collisions
Earth’s temperature dropped below 1,000 ۫C
First rocks formed as crust cooled
The oldest Earth rocks currently known are 3.8 billion years old.
The oldest meteorites and lunar rocks are about 4.5 billion years old
Erosion and plate tectonics have probably destroyed all of the Earth rocks older than 3.8 billion years.

7. The Archaean Eon: 3.8 - 2.5 billion years ago
Began with the formation of solid rock
Volcanic activity added heavier gasses to atmosphere (CO2, N2)
Water condensed
Early oceans formed
First life appeared on Earth

8. Gasses given off by volcanoes
Water Vapor --> % Carbon Dioxide --> 24%
Sulfur --> 13% Nitrogen --> 5.7%
Argon --> 0.3% Chlorine --> 0.1%
What is missing?

9. Eon Review: 1) Precambrian – 3 parts a) Hadean b) Archean
c) Proterozioc
2) Phanerozic – 3 parts
a) paleozoic
b) mesozic
c) cenozoic

10. First Life….. 1) Proterozoic Eon = first animals
**Before animals there were
many types of
unicellular organisms
single celled living things
2) Phanerozoic Eon =
(starts with Paleozoic Era
and cambrian explosion)
many animals appear

11. 1st living thing =Bacteria
3.4 byo, South Africa
1) Prokaryotic=
before nucleus
2) Heterotrophic:
eat food(not photosynthetic)
3) anaerobic:
no O2
4) fermenters:
use organic molecules for chemical energy
waste = alcohol + CO2
modern

12. 2nd living things Archaebacteria
extremohiles
very similar to earliest life forms
live in “extreme” environments
1) Anaerobic environments
2) Extreme high temperature
(thermophilic)
3) Extreme high salt
(halophilic)

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

14. Deep Ocean boiling water from vents through crust
very stable environment
very protected
lots of minerals
warm -> hot
Archaebacteria

15. The First Energy Crunch
organic molecules run low
Natural selection for….
organisms that make their own food
crisis solved by origin of
_____________
Photosynthesis

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

17. What Likely Happened O2 made by cyanobacteria at ocean surface
O2 toxic to them
but not if the O2 was removed by bonding with iron (Fe)
Oceans contained dissolved iron

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

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

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

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

22. BIFs (Banded Iron Formations)
thick (100s of feet) deposits
Precambrian,
Australia

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

24. Oxygen Crisis eventually, oxygen built up in oceans
then outgassed into the atmosphere
oxygen atmosphere led to first major mass extinction
anaerobic bacteria restricted to refuges (stagnant water, deep soils, etc.)

25. Aerobic Bacteria some bacteria evolved antioxidant mechanisms
allowed those bacteria to tolerate rising O2 levels
some bacteria even evolved to use O2
(aerobic respiration)

26. How Far Back Does the Fossil Record Extend?

27. 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

28. Almost Certainly
900 myo - Australia
Bitter Springs Formation

29. Likely
byo - South Africa
Fig Tree Group

30. 3.5 byo - Australia Maybe? Modern cyanobacteria for comparison
Warrawoona Group, Australia

31. Living
Precambrian
Cyanobacteria
Ancient vs. Modern

32. 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 altered the face of the planet

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

34. Stromatolites dome-shaped, layered structures some 3.5 byo
made of layers of bacteria
produce abundant oxygen
how do we know?

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

36. 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

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

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

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

42. 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

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

44. Cyanobacteria and the build up of oxygen in the Earth’s atmosphere had 4 significant effects:
1. start of producer based food chain
2. first mass extinction
3. allowed aerobic respiration which let organisms make enough energy to be multicellular
4. Oxygen in air turned into Ozone (O3) Ozone protection from U-V let organisms move onto land