ORIGIN OF LIFE
Theories Past and Present
Nature of Early Cells
Evolution of Cells
RiverDell High School
Biology
I. Abiogenesis or Biogenesis ?
Scientists Debate
A. Abiogenesis - life can arise from
nonliving things
B. Biogenesis – life can arise only
from living things
C. Redi’s Experiment
(1621-1697)
1. control – uncovered jars with meat
2. experimental group – jars with meat
covered with netting
3. results – maggots only in control
4. conclusion – flies come from eggs
laid by other flies
Redi’s Experiments
D. Spallanzani’s Experiment
(1729-1799)
1. control – flask with boiled broth is
left open
2. experimental group – flask with
boiled broth is sealed immediately
3. results – open flask became cloudy
closed flask remained clear
4. microrganisms came from the air
Spallanzani’s Experiment
E. Pasteur’s Experiment
(1822-1895)
1. broth boiled in a flask with a curved
neck
2. after one year the broth stayed clear
3. when the necks were broken the
broth became cloudy
4. conclusion – the air is the source of
microorganisms
Pasteur
GREAT WEBSITE ON PASTEUR'S EXPERIMENT
http://bcs.whfreeman.com/thelifewire/content/chp03/0302003.html
Describes and animates the experiment of Louis Pasteur. Has quiz at the end,
asks questions on what YOU THINK we’ll happen before each step, animates
experiment well.
II. Earth’s History
A. Solar System begins to form 5 billion
years ago
B. Sun begins to form a few million
years later
C. Earth forms - 4.6 billion years ago
D. Volcanoes form earth’s atmosphere
E. 2.2 billion years ago earth like today
Formation of the Solar System
Began 5 billion Years Ago
• Planet Earth
formed 4.6
billion years ago
• conditions were
very different
• 2.2 billion years
ago Earth was
similar to the
planet we live on
today
III. Evolution of Life
A. Origin of Organic Compounds
1. Early atmosphere – ammonia (NH3)
hydrogen gas (H2), water vapor
(H2O) and methane gas (CH4)
2. High temperatures, frequent volcanoes,
electrical storms, and comets
3. Maybe some organic compounds came to
to earth from space
Early Earth
III. Evolution of Life
A. Origin of Organic Compounds
4. Oparin and Haldane
a. early gases and high temperatures
formed simple organic compounds
that collected in water and reacted
to form macromolecules necessary
for life
Conditions – Early Earth
III. Evolution of Life
A. Origin of Organic Compounds
5. Urey and Miller (1953)
a. experiment to test Oparin’s
hypotheses
b. chamber with early gases and
electric sparks form several organic
compounds
c. similar experiments formed amino
acids, ATP and nucleotides
Urey-Miller Experimental Apparatus
Urey-Miller Experiment
http://www.ucsd.tv/miller-urey/
http://www.ucsd.tv/miller-urey/
III. Evolution of Life
A. Origin of Organic Compounds
6. Other Hypotheses
a. early atmosphere composed of
carbon dioxide, nitrogen, hydrogen
water vapor
b. early life may have formed in
chemicals found in thermal vents
found at the bottom of the ocean
Origin of Life - Thermal Vent Hypothesis
III. Evolution of Life
B. Cell Like Structures Form
1. Solutions of organic compounds can
form coacervates (collection of
droplets of amino acids, sugars and
lipids)
2. Microspheres – spherical forms
surrounded by a protein membrane
3. Both do not have all properties of life
Sidney Fox and others
researched structures
which may have formed
early cells
Evolution of Life
C. The First Cells
1. First cells were probably anaerobic
heterotrophs
2. Similar to some prokaryotes
3. Eventually competition for organic
molecules gave autotrophs an
adaptive advantage
Evolution of Life
C. The First Cells
4. Chemosynthetic organisms evolve
a. get energy from oxidation of
inorganic substances
b. carbon dioxide used to make
organic molecules that store
energy
Evolution of Life
C. The First Cells - The RNA World
5. Self-replicating RNA molecules may
have evolved first
6. Ribozyme – RNA that can act as a
catalyst – even for self-replication
7. Maybe first case of heredity and
competition
Thomas Cech
The Ribozyme
Evolution of the First Cells
D. Photosynthesis Evolves
1.About 3 billion years ago
2. Organisms similar to cyanobacteria
3. Oxygen is a product that might
damage some types of cells
4. Ozone layer forms from the oxygen
a. reduces ultraviolet light
Present Day
Cyanobacteria
Ancient
Cyanobacteria
Stromatolites Formed
by Cyanobacteria
Carbon Deposits from
Ancient Cyanobacteria
Formation of the Ozone Layer
• Cyanobacteria
release oxygen in the
atmosphere
• O2 is converted to
O3 (ozone) in the
upper atmosphere
• Ozone layer blocks
much of the UV light
• Allows life to move
from the sea to land
Changes of O3 Concentrations
Between 1980 and 1991
Changes in Ozone Concentrations
Between 1970 and 1998
E. Aerobic Respiration Evolves
1. More than one billion years before
oxygen to reached current levels
2. Early function of aerobic respiration
may have been to prevent oxygen
from destroying essential organic
compounds
F. Endosymbiosis
Evolution of Eukaryote
1. 1.5 – 2.0 billion years ago
2. Aerobic prokaryote took residence
inside a larger anaerobic prokaryote
a. became the mitochondria
3. photosynthetic cyanobacteria may
have evolved into chloroplasts
F. Endosymbiosis
Evolution of Eukaryotes
4. Evidence of endosymbiosis
a. both mitochondria and chloroplast
1) replicate independently from
cell cycle
2) have their own genetic
material
3) circular DNA like prokaryotes
Lynn Margulis – Theory of
Endosymbiosis
Endosymbosis and Cell Evolution
Endosymbiosis and the Nucleus
Three Cell Organelles Formed by
Endosymbiosis
Comparing Prokaryote and Eukaryote
Evolution From Prokaryotes to Eukaryotes
• The first cells were
probably like
Eubacteria or
Archaebacteria
(formely known as
Monera)
• Unicellular eukaryotes
came next
• Then multicellular
eukaryotes evolved
Evolution of The Kingdoms
Cladogram of Evolutionary Relationships
IV. Radioactive Decay and Dating
A. Isotope – atoms of the same element
that differ in the number of neutrons
B. Radioactive decay – process in which
unstable nuclei release particles and/or
energy until they are stable
C. Half-life – the length of time it takes for ½
any amount of a radioactive isotope to
decay
Half-lives
256 14C atoms
at time 0
Half-lives
128 14C and
128 14N atoms
after 5,600
years or
1 half-life
Half-lives
64 14C and
192 14N atoms
after 11,200
years or
2 half-lives
Half-lives
32 14C and
224 14N atoms
after 16,800
years or
3 half-lives
Half-lives
16 14C and
240 14N atoms
after 22,400
years or
4 half-lives
Half-lives
8 14C and
248 14N atoms
after 28,000
years or
5 half-lives
Half-lives
4 14C and
252 14N atoms
after 33,600
years or
6 half-lives
Half-lives
2 14C and
254 14N atoms
after 39,200
years or
7 half-lives
Proportion of isotope left
• The half-life of C-14 is 5,600 years and a sample
today has 1,000 C-14 atoms, after 5,600 years 
500 C-14 atoms will remain (1/2 original amount)
• After two half lives (11,200 years) 
250 C-14 atoms will remain (1/4 original amount)
1
1/2
1/4
1/8
1/16
0
1
2
3
Half-lives
4
5
IV. Radioactive Decay and Dating
D. Hyphen notation of radioisotopes
(element symbol and mass number)
- examples (C-12, C-14, O-16, O-18)
E. Carbon-14 dating – compare ratio
of C-14 and C-12 and use the ratio to
determine age
IV.Radioactive Decay and Dating
ISOTOPE
Carbon-14
Uranium-235
Potassium-40
Uranium-238
HALF LIFE (years)
5,730
704,000,000
1,250,000,000
4,500,000,000
A. Problem Solving
1. The half-life of thorium-230 is
75,000 years. If a scientist has 40.0g
of thorium, how much will remain
after 225,000 years?
B. Half Life Problem Solving
2. The half life of carbon-14 is 5,370
years. How long will it take for ½ of
the sample to decay?
3. If a biologist has 64.0g of C-14, how
long will it take until 8.0g remain undecayed?