2/27/2011
Activating Strategy
• Think About It:
– What makes something living?
AP Lesson #66
EQ: What theories have been proposed
to explain the origin of life on earth?
500
Millions of years ago
1000
1500
2000
2500
3000
3500
Cenozoic
Mesozoic
Paleozoic
ARCHEAN
PROTEROZOIC
PRECAMBRIAN
0
Colonization of land
by animals
Appearance of animals
and land plants
First multicellular
organisms
Bacteria Archae- Protista Plantae Fungi
bacteria
Animalia
Oldest definite fossils
of eukaryotes
Appearance of oxygen
in atmosphere
Oldest definite fossils
of prokaryotes
4000
Molten-hot surface of
earth becomes cooler
4500
Formation of earth
The evolutionary tree of
life can be documented
with evidence.
The Origin of Life on
Earth is another story…
1
2/27/2011
What is Life?
• First we have to define LIFE…
–
–
–
–
–
organized as cells
respond to stimuli
regulate homeostasis
Coordinate metabolism
develop
• change & mature
within lifetime
– reproduce
• heredity
• adaptation & evolution
The Origin of Life is a Hypotheses
• Special Creation
– Was life created by a supernatural or
divine force?
– not testable
• Spontaneous Abiotic Origin
– Did life evolve spontaneously from
inorganic molecules?
– testable
• Extraterrestrial Origin
– Was the original source of organic
(carbon) materials comets &
meteorites striking early Earth?
– testable
How is the origin of life possible?
• Chemical and physical processes on early Earth
may have produced very simple cells through a
sequence of stages:
1. Abiotic synthesis of small organic molecules
2. Joining of these small molecules into
macromolecules
3. Packaging of molecules into “protobionts”
4. Origin of self-replicating molecules
2
2/27/2011
When did life begin?
• ~3.5 bya the first prokaryotes
are found in the fossil record
– Heterotrophic
– Competition for organic
molecules
3.5 billion year old fossil of bacteria
modern bacteria
chains of one-celled
cyanobacteria
Stromatolites
Fossilized mats of
prokaryotes resemble
modern microbial colonies
How did we get an oxygenated atmosphere?
• ~ 2.7 bya mutation resulted in photosynthetic
bacteria
– oxidizing atmosphere
• evidence in banded iron in rocks = rusting
• Aerobic respiration possible (Lots more ATP!)
3
2/27/2011
What lead to the origin of eukaryotes?
• ~ 2bya development of internal membranes
– created specialization
– advantage: increase efficiency
infolding of the
plasma membrane
endoplasmic
reticulum (ER)
plasma
membrane
nuclear envelope
nucleus
DNA
cell wall
Prokaryotic
ancestor of
eukaryotic
cells
Prokaryotic
cell
plasma
membrane
Eukaryotic
cell
How did mitochondria originate?
• Endosymbiosis
– aerobic bacteria was engulfed, but was not
digested
– Mutualistic relationship
internal membrane
system
aerobic bacterium
mitochondrion
Endosymbiosis
Eukaryotic cell
with mitochondrion
Ancestral
eukaryotic cell
How did chloroplasts originate?
• origin of chloroplasts
• engulfed photosynthetic bacteria,
but did not digest them
• mutually beneficial relationship
Eukaryotic
cell with
mitochondrion
Endosymbiosis
photosynthetic
bacterium
Eukaryotic cell
with
chloroplast &
mitochondrion
chloroplast
mitochondrion
4
2/27/2011
What evidence supports endosymbiosis?
• Structural
– resemble bacteria
• Genetic
– have their own circular
DNA
• Functional
Lynn Margulis
– move freely within the cell
– reproduce independently
What’s the next big change?
• ~ 543 mya diversification of Animals
– within 10–20 million years most of the major phyla of
animals appear in fossil record
~ 90,000 years ago Modern Humans
Colonization
of land
Animals
Origin of solar
system and
Earth
4
1
Proterozoic
2
Archaean
Heterotrophic
Prokaryotes
3
Multicellular
eukaryotes
Single-celled
eukaryotes
Autotrophic Prokaryotes
Atmospheric oxygen
5
2/27/2011
Summarizing Strategy
• 3 – 2 – 1:
– 3 most important things learned
– 2 questions that you still wonder
– 1 way this information connects to what you know
Assessment
• HW: Chapter 25 Wkst and Read/Skim
Chapter 26
Colonization
of land
4
1
Proterozoic
2
Archaean
3
6
2/27/2011
How did cells originate?
• Protobionts
– abiotically produced molecules surrounded by a
membrane–like structure
• Bubbles → separate inside from outside
→ metabolism & reproduction
How did Genetics originate?
• RNA is likely first genetic material
• Multi-functional
– codes information
• self-replicating molecule
• makes inheritance possible
• natural selection & evolution
– enzyme functions
– regulatory molecule
– transport molecule
Dawn of natural selection
What were the conditions like on early Earth?
• Reducing atmosphere
– water vapor (H2O), CO2, N2, NOx, H2, NH3, CH4,
H2 S
– lots of available H & electrons
low O2 =
organic molecules
– low oxygen
• Energy source
do not breakdown
as quickly
– lightning, UV radiation,
volcanic
7
2/27/2011
How did organic molecules
originate?
Electrodes discharge
sparks
(lightning simulation)
• Abiotic synthesis
– 1920
Oparin & Haldane
propose reducing
atmosphere hypothesis
– 1953
Miller & Urey
test hypothesis
CH4
Water vapor
NH3
Mixture of gases
("primitive
atmosphere")
H2
Condenser
Water
• formed simple amino
acids
– adenine
Heated water
("ocean")
Condensed
liquid with
complex,
organic
molecules
Stanley Miller
University of Chicago
Click for Video
8