Earth History
• 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
1. The Hadean Eon:
• 4.6 to 3.8 billion years ago
• Earth & other planets formed from dust and
gasses surrounding the sun
• 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
• 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.
• 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.
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
Gasses given off by volcanoes
• Water Vapor --> 50--60% Carbon Dioxide --> 24%
• Sulfur --> 13%
Nitrogen --> 5.7%
• Argon --> 0.3%
Chlorine --> 0.1%
• What is missing?
Eon Review:
• 1) Precambrian – 3 parts
•
a) Hadean
•
b) Archean
•
c) Proterozioc
• 2) Phanerozic – 3 parts
•
a) paleozoic
•
b) mesozic
•
c) cenozoic
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
1st living thing =Bacteria
1) Prokaryotic=
•
before nucleus
3.4 byo, South Africa
• 2) Heterotrophic:
•
eat food(not photosynthetic)
• 3) anaerobic:
•
no O2
• 4) fermenters:
use organic molecules for chemical energy modern
waste = alcohol + CO2
2nd living things
Archaebacteria
very similar to earliest life forms
• live in “extreme” environments
• 1) Anaerobic environments
• 2) Extreme high temperature
•
(thermophilic)
• 3) Extreme high salt
•
(halophilic)
Hot Springs
• Conditions very like Archean Earth
• High Temperatures
• Low free oxygen
• Archeabacteria live here today
Deep Ocean
•
•
•
•
•
•
boiling water from vents through crust
very stable environment
very protected
lots of minerals
warm -> hot
Archaebacteria
The First Energy Crunch
• organic molecules run low
• Natural selection for….
•
organisms that make their own food
• crisis solved by origin of
Photosynthesis
• _____________
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
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
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
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
Why are BIFs Banded? When runoff
added more Fe to the water the entire
process stared over again.
Banded Iron Formations
Indirect (non-fossil) evidence
for the presence of
cyanobacteria ~ 3.5 bya
BIFs (Banded Iron Formations)
• thick (100s of feet) deposits
Precambrian,
Australia
BIFs
• began forming about 3.5 bya = 1st free O2
• reached peak about 2.5 bya
• deposition ended about 1.8 bya
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.)
Aerobic Bacteria
• some bacteria evolved antioxidant
mechanisms
• allowed those bacteria to tolerate rising
O2 levels
• some bacteria even evolved to use O2
• (aerobic respiration)
How Far Back Does the Fossil
Record Extend?
Bacterial fossils preserved in the act of division.
~3.4 billion years old, South Africa
modern bacteria in similar
stages of division
2.1 Billion years old, Hudson Bay, Canada
Almost Certainly
900 myo - Australia
Bitter Springs Formation
Likely
3.1 - 3.2 byo - South Africa
Fig Tree Group
3.5 byo - Australia
Warrawoona Group, Australia
Maybe?
Modern cyanobacteria
for comparison
Living
Cyanobacteria
Ancient vs.
Modern
Precambrian
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
Earliest (Undisputed)
Evidence of Life Stromatolites
2.2 byo Michigan
Stromatolites
• dome-shaped, layered structures
• some 3.5 byo
• made of layers of bacteria
• produce abundant oxygen
• how do we know?
They are still alive today in special
environments, notably Shark Bay, Australia
Tide In
Tide Out
Formation of Stromatolites
Cyanobacteria form a mat
on top of sediment
1 cm
A new layer of sediment
is deposited on top
Bacteria grow up
through new layer
Stromatolites provide
evidence for the
occurrence of
cyanobacteria in the
fossil record.
Modern
Ancient
• if we use stromatolites to infer
presence of cyanobacteria
• we might expect to find fossils
bacteria-like organisms in them...
the
of
And we often find them . . .
Gunflint Chert (~2.0 billion years old), Canada
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
Order of Appearance of Life
Forms
•
•
•
•
•
•
•
•
First =
heterotrophic/anaerobic bacteria
Second =
heterotrophic/anaerobic Archaebacteria
Third =
photosynthetic cyanobacteria
Fourth =
Aerobic bacteria
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