Origin of
living
Things
and
Natural
Selection
DBQ
• Around 30 000 species of vertebrate
animals with four limbs (tetrapods) are
found today. They are thought to have
evolved from a single amphibian
species that crawled on to land
around 400 million years ago during
the Devonian geological period. The
graph shows how the number of
families of tetrapod species varied in
each geological period since their first
appearance.
(a)State in which geological period reptiles first appeared. [1]
(b) Calculate how many families of mammal were present
five million years ago.
[1]
(c) Analyze the data in the graph to conclude whether
mammals are more likely to have evolved from birds or
from reptiles.
[1]
(d) Suggest how scientists collected the data about the
numbers of families.
[1]
(e) The junction between the Cretaceous and Tertiary periods is
called the K–T boundary. Using the data in the graph, discuss
whether evolution at the K–T boundary fits the hypothesis of
punctuated equilibrium or gradualism more closely.
[8]
(mammal/bird; at a constant or gradual rate; amphibian/reptile; Tertiary; rapid bursts;
species; stability; Cretaceous)
In punctuated equilibrium evolution occurs in _______________
interspersed by long periods of _____________ . The evidence
shows very little change in number of __________________
families occurred during ____________________ period but large
increase during the _________________ period. In gradualism
evolution occurs _______________. The evidence shows the
number of _____________________ families did not change
much but a change in the number of families do not reflect what
happens at the ____________________ level.
The Origin
of Organic
Molecules
and Life
(A Scientific Perspective)
Origin of Life
and Organic
Molecules
(The Scientific
Perspective)
1500
2000
2500
3000
3500
ARCHEAN
Millions of years ago
1000
Paleozoic
Bacteria Archae- Protista Plantae
bacteria
Fungi
Animalia
Colonization of land
by animals
Appearance of animals
and land plants
First multicellular
organisms
Oldest definite fossils
of eukaryotes
PRECAMBRIAN
500
Cenozoic
Mesozoic
PROTEROZOIC
0
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…
The Origin of Life is a
• Extra-terrestrial Origin
– Was the original source of organic
(carbon) materials comets &
meteorites striking early Earth?
– Testable
• Spontaneous Abiotic Origin
– Did life evolve spontaneously from
inorganic molecules?
– Testable
Hypothesis
Abiotic Origin of Life
• Water vapor condensed (did not crystallize) - Formed
oceans
-Contained chemicals of life (primordial soup)
• Most researchers believe life first appeared in shallow water
or moist sediments.
• However some now feel the first organisms may have
developed on the sea floor due to the harsh conditions on
the surface during that time.
• This position was strengthened in the 1970's by the
discovery of the deep-sea vent communities.
• Hot water and minerals emitted from such deep-sea
volcanic vents may have provided the energy and chemicals
necessary for development of the early protobionts.
Conditions on early Earth
• Reducing atmosphere: this enhanced the joining of
simple molecules to form more complex ones
– water vapor (H2O), CO2, N2, NOx, H2, NH3, CH4,
H2S
– lots of available Hydrogen & its electron
– no free oxygen
• Energy sources - lightning, UV radiation, volcanic
What’s missing
from that
atmosphere?
A: Atmosphere was
almost devoid of oxygen
(which steals electrons
away from other
atoms).
Origin of Organic
Molecules
• Abiotic synthesis
– 1920
Oparin & Haldane
propose reducing
atmosphere
hypothesis
– 1953 Miller & Urey
test hypothesis
• formed organic
compounds
Stanley Miller
University of Chicago
Produced:
-amino acids
-hydrocarbons
-nitrogen bases
-other organics
• The findings were significant for a number of
reasons:
Why was
The early Earth could not have had oxygen present
this
(supported by other geological evidence)
experiment • The early Earth had conditions that could have
important??!
allowed for the generation of molecules that would
sustain life
• Other variations of the experiment showed that
molecules that could be used in DNA and RNA
could be produced.
• So this experiment supports the
chemosynthetic theory, but because we weren't
there to observe it, it is NOT proven.
Spontaneous Origin of Life on Earth
• Life is defined partly by two properties: accurate replication and
metabolism. Neither property can exist without the other. Self–replicating
molecules and a metabolism–like source of the building blocks must have
appeared together. How did that happen?
• Four processes needed for the spontaneous origin of life on Earth
– The non-living synthesis of simple organic molecules
– The assembly of these molecules into polymers
– The origin of self replicating molecules that made inheritance possible
– The packaging of these molecules into membranes with an internal
chemistry different from their surroundings
• The necessary conditions for life may have been met by protobionts,
aggregates of abiotically produced molecules surrounded by a membrane
or membrane–like structure.
• Protobionts exhibit some of the properties associated with life, including
simple reproduction and metabolism, as well as the maintenance of an
internal chemical environment different from that of their surroundings.
Key Events in Origin of Life
• Origin of Cells (Protobionts)
– lipid bubbles  separate inside from outside w/metabolism &
reproduction
Laboratory experiments demonstrate that protobionts could have
formed spontaneously from abiotically produced organic compounds.
For example, small membrane–bounded droplets called liposomes can
form when lipids or other organic molecules are added to water.
• Origin of Genetics
– RNA is likely first genetic material
– multiple functions: encodes information (self-replicating), enzyme,
regulatory molecule, transport molecule (tRNA, mRNA)
• makes inheritance possible
• makes natural selection & evolution possible
• Origin of Eukaryotes
– endosymbiosis
First Eukaryotes
~2 bya
• Development of internal membranes
– create internal micro-environments
– advantage: specialization = increase efficiency
• natural selection!
infolding of the
plasma membrane
plasma
membrane
endoplasmic
reticulum (ER)
nuclear envelope
nucleus
DNA
cell wall
Prokaryotic
cell
Prokaryotic
ancestor of
eukaryotic
cells
plasma
membrane
Eukaryotic
cell
1
st
Endosymbiosis
• Evolution of eukaryotes
– origin of mitochondria
– engulfed aerobic bacteria, but
did not digest them
– mutually beneficial relationship
• natural selection!
internal membrane
system
aerobic bacterium
mitochondrion
Endosymbiosis
Ancestral
eukaryotic cell
Eukaryotic cell
with mitochondrion
2
nd
Endosymbiosis
• Evolution of eukaryotes
Eukaryotic
cell with
mitochondrion
– origin of chloroplasts
– engulfed photosynthetic bacteria,
but did not digest them
– mutually beneficial relationship
• natural selection!
photosynthetic
bacterium
chloroplast
Endosymbiosis
Eukaryotic cell with
chloroplast & mitochondrion
mitochondrion
Theory of Endosymbiosis
• Evidence
– structural
• mitochondria & chloroplasts
resemble bacterial structure
– genetic
• mitochondria & chloroplasts
have their own circular DNA, like bacteria
– functional
• mitochondria & chloroplasts
move freely within the cell
• mitochondria & chloroplasts
reproduce independently
from the cell
Lynn Margulis
Cambrian explosion
• Diversification of Animals
The Day the Mesozoic Died
– within 10–20 million years most of the major phyla of
animals appear in fossil record
543 mya
Extraterrestrial Life?
“Hmmmm…..
Life on other planets
is there?”
Seeding the Universe – ClEvR Graphic Organizer (on wiki)
Scientific Explanation to Origin of Life
• Panspermia -- some organic compounds may have reached
Earth by way of meteorites and comets.
– Organic compounds (e.g., amino acids) have been recovered
from modern meteorites.
• These extraterrestrial organic compounds may have contributed
to the pool of molecules that formed early life (seeds of life are
prevalent throughout the universe and life on Earth began by
such seeds landing on Earth and propagating).
• There is some evidence to suggest that bacteria may be able to
survive for very long periods of time even in deep space (and
may therefore be the underlying mechanism behind Panspermia).
• Streptococcus mitus bacteria that had accidentally been taken to
the moon on the Surveyor 3 spacecraft in 1967, could easily be
revived after being taken back to earth three years later.
Origin of Life Assignment
The Origin of Life Challenge