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History of Life on Earth
Chapter 12
The Age of the Earth
4.5 billion years old
– Radiometric dating
– Radioactive isotopes break
down over time
– Half-life – time it takes for half
of amount to decay
– Using this can estimate age of
Non-living chemicals reacted
and produced organic
Combination of chemicals
and energy from
lightning/heat/Sun’s UV
created organic molecules
2 Theories about how
Primordial Soup
Oceans filled with
organic molecules
 Sparks simulate
 Amino acids, fatty
acids. And other
hydrocarbons formed
 1 problem: no ozone
to protect from UV,
certain compounds
couldn’t have existed
Bubble Model
Gases from undersea
volcanoes trapped in
bubbles that protect
them from UV and
concentrate them
Reactions happen
Bubbles rise, burst,
release compounds
Energy from UV and
lightning creates more
Complex organic
molecules fall into
ocean and start again
Precursor of
Molecules of life can arise from simple chemistry
 RNA can be made in lab
 RNA believed to be 1st self-copying information
storing molecule
 Makes proteins and changes from generation to
generation; acts as an enzyme
– Amino acid chains
form droplets in water
– Droplet made of
different kinds of
molecules like amino
acids and sugars
These are steps
toward cellular
 Microspheres last
longer and longer and
bring other molecules
Origin of Heredity
DNA came after RNA
 RNA catalyzed early proteins
 Many believe RNA was brought into
microsphere and could pass traits on
 But how DNA, RNA, and hereditary
mechanisms first developed is still not
12.2 The Evolution of Cellular Life:
Fossil preserved or
mineralized remains or
imprints of an
organism that lived
long ago
 Oldest (2.5 billion years
old) photosynthetic
prokaryotes cyanobacteria
 Created oxygen but
took millions of years
to build up to current
Two Groups of Bacteria Split Very Early
– Peptidoglycan in cell
– Many cause disease
and decay
– No peptidoglycan
– Unique lipids in cell
– Believed to resemble
ancient archaebacteria
Evolution of Eukaryotes
1.5 bya first eukaryotes showed up
 Larger; internal membranes; DNA in
– Mitochondria in almost all
– Chloroplasts in plants and protists
Theory states bacteria entered large cells
as parasites or undigested prey
 Begin to live inside host and performed
cellular respiration or photosynthesis
 Mitochondria – descendents of symbiotic,
aerobic eubacteria
 Chloroplasts – descendents of symbiotic,
photosynthetic eubacteria
Support for Endosymbiosis
Size and Structure
– Mitochondria like eubacteria
– Chloroplasts like cyanobacteria
Genetic Material
– Circular DNA similar to bacteria is different
than hosts DNA
– Similar in size to those of bacteria
– Simple fission independent of host
All living things are broken into 6 kingdoms
– Eubacteria, Archaebacteria, Protista, Fungi, Plants, Animals
Eubacteria and Archaebacteria oldest; single celled prokaryotes
Protista – first eukaryotic kingdom, multicellular and unicellular
All other eukaryotes, fungi, plants, and animals, came later and
all came from protists
Unicellular is very successful
 Almost every cell you can see is
Origins of Modern Organisms
Cambrian Explosion
– Most animal phyla originated during late Precambrian
and early Cambrian periods
– Great evolutionary expansion
– Many unusual marine organisms appear that have no
living relatives
Burgess Shale
1909 geological formation in Canada found
 Ordovician Period – 505 mya – 438 mya
– Trilobites – extinct 250 mya
Burgess Shale
Mass Extinctions
Large number of species become extinct
 5 Major extinctions
440 mya
360 mya
245 mya – 96% of all species
210 mya
65 mya – 2/3 of all land species
Today? Human activity might be causing another
– ½ of rainforests destroyed
– Keep up our current rate
 22% to 47% of plants gone
 2,000 of the 9,000 birds
12.3 Life Invaded Land
Ozone Layer
– Life evolved protected in
oceans from dangerous
UV rays from Sun
– No life on land during
Cambrian period
– 2.5 bya photosynthesis
puts O2 into air which
reacts and forms Ozone,
– Blocks UV
– Eventually enough to
make it safe to live on
Plants and Fungi on Land
1st organisms on land
were probably a
combination of plants
and fungi; 430 mya
– Plants can make nutrients
by photosynthesis
– Fungi can absorb minerals
from rock
– Together called
mycorrhizae, these exist
Mutualism – 2 species
live together and both
Theory of Evolution
Chapter 13
13.1 The Theory of Evolution by
Natural Selection
Before Darwin most
people believed each
species was a divine
creation existing as it
was when it was
 But why were there
fossils of unknown
Jean Baptiste
Lamarck 1809
– Features of organisms
change during life and
are passed on to
– Giraffe stretches neck
to reach leaves,
offspring have longer
And now for Darwin
Charles Darwin was from
a wealthy family
Studied medicine but
became a minister
(though he never
became ordained)
In 1831 Darwin went on
a voyage on the HMS
Beagle as a naturalist
Galapagos Islands –
plants and animals
resembled those of the
coast of South America
Darwin believed the
organisms arrived
from the coast and
changed once they
were there
 Called this “descent
with modification”
which would become
known as evolution
 Most famous were the
finches and the
 He studied the data
he collected for many
Things That Affected Darwin
Charles Lyell book
– Principles of Geology
– Surface of Earth
changed over time
Thomas Malthus
essay 1798
– Human population was
increasing faster than
its food source
– Unchecked populations
will grow geometrically
– Humans are checked
by disease, war, &
Populations are all of the individuals of a
species that live in a specific geographical
area and can interbreed
 Darwin believed Malthus’s idea of
unchecked population growth applied to
all species
 “Individuals that have physical or
behavioral traits that better suit their
environment are more likely to survive and
will reproduce more successfully than
those that do not have such traits”
Evolution By Natural Selection
Natural Selection –
Number of individuals
with favorable
characteristics that
are inherited will
 Adaptations are
inherited traits that
become common
because it produces a
selective advantage
Publication of Darwin’s Work
1831 – Beagle voyage
 1844 – very low public
opinion of evolution
 1859 – Another
scientist, Alfred Russel
Wallace, writes Darwin
asking for help to
publish his work that
describes natural
 Darwin publishes his
work and people aren’t
happy to hear they are
“related to apes”
Major Points of Theory
Inherited variation exists within the genes
of every population or species
 In environments, some individuals are
better suited and have more offspring
 Beneficial traits spread
 Evidence that living species evolved from
extinct organisms
Now know genes are responsible for
inherited traits
 Natural selection causes the frequency of
certain alleles in a population to increase
or decrease over time
Species Formation
Reproductive Isolation
– 2 populations of the
same species do not
breed with each other
due to geographic
separation, difference
in mating periods, or
other barriers
– Eventually they may
not be able to breed
with each other
– Kaibab squirrel and
Abert squirrel
Tempo of Evolution
– Slow/gradual process
of changing that
occurs continuously
– Large changes that
occur quickly
13.2 Evidence of Evolution
– Many intermediate life
forms have been found
in fossils
– Not complete
– Certain environments
are better for forming
– Animals that live in
areas that are not
good for fossils are
– Studied by
Anatomy and development
– Comparisons can show similarities
– Vestigial structures
 Structures that have no use or have a less important function
than they do in other related organisms
 Whale’s hind limbs
 Humans appendix
Vestigial Structures
– Share a common
– Similar structure in
different organisms
Development of
– Believe you can see
evolutionary history
– At some point all
vertebrates have a
tail, buds that
become limbs, and
Biological Molecules
– Proteins
 Smaller differences between closely related and
larger between more distantly related
– DNA sequences
 Similar to relationships predicted by biologists
13.3 Examples of Evolution
Factors in Natural Selection
– All populations have genetic variation
– The environment presents challenges to
successful reproduction
– Individuals tend to produce more offspring
than the environment can support
– Better suited individuals leave more offspring
Example of Natural Selection
Tuberculosis (TB) kills more adults than
any other infectious disease
 Antibiotics introduced in 50s now don’t
work because bacteria are resistant
 Mutation in some bacteria made it
resistant so it survived and passed on
genes and becomes more common in
Evolution in
Darwin’s Finches
– Darwin collected
31 specimens
from 3 islands
– 9 distinct species
all similar except
for bills
 Large bills fed on
 Small bills ate
Formation of New Species
Divergence – accumulation of differences
between groups
 Speciation – process by which a new
species forms
 Subspecies – populations of the same
species that differ genetically because of
adaptations to different living conditions
– First step of speciation
Maintaining New Species
– When subspecies become different enough a
reproductive barrier may form
– Geographic isolation
– Different reproduction times
– Physical differences
– Offspring not fertile