Download Chapter 14 The History of Life

Earth is 4.6 billion years old
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After the Bang, earth formed from hot gases
and debris
Atmosphere formed from gases spewing from
volcanoes.
No oxygen, nitrogren, water vapor, carbon
dioxide, hydrogen sulfide, hydrogen cyanide –
toxic to life as we know it.
4.4 billion years ago, earth began to cool and
oceans formed from condensing water vapor
causing millions of years of rain.
Meteorites containing organic molecules were
colliding with earth.
Life originated on earth between
3.9 and 3.4 billion years ago.
The fossil record is indirect proof of the
age of the earth.
 Fossils are the remains of past life on
earth.
 Fossils are found in sedementary rock.
 Usually only hard body parts can make
fossils, therefore there are many missing
links in the fossil record.
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How do fossils help us understand
the History of the earth?
By comparing the fossils of past life with
today’s life we can make deductions about
what the environment was like in the past.
 For example, if fossils look like plants or
animals that are found today in tropical
regions than that may tell a scientist that
the climate in that was once tropical.
 Scientists who study the remains of life past
are called paleontologists.
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Relative Dating.
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In undisturbed layers of sedimentary rock, the
rock layers at the surface are younger than
those that are deeper and therefore the fossils
found in the top layers must also be younger
than the fossil found in lower layers.
Relative dating cannot give an
exact age; it can only arrange
the fossils in order of
appearance on earth.
Radiometric dating
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Radiometric dating is also called Absolute Dating,
because it can give the actual date of rocks in which
the fossils have been found and an actual age of the
fossils.
Radiometric dating uses the fact that radioactive
isotopes found in rocks will decay at a set rate. This
is called a half-life.
In one half-life, half of the radioactive isotopes will
have changed into a non-radioactive form .
By looking at how much of the radioactive isotope is
left, scientist can determine the age of the rock
and/or fossil.
Some common isotopes used to
date rocks and fossils.
Carbon 14 will decay into nitrogen 14 with a
half-life of 5730 years.
 Potassium 40 will decay into Argon 40 with a
half-life of 1.3 billion years.
 Carbon 14 is used to date fossils less than
50,000 years old.
 Potassium 40 can be used to date the oldest
rocks on earth.
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Geologic Time
The Geologic Time Scale is divided by the
organisms that lived during the time interval.
 It is based on the evidence of fossils and the
earth’s rocks.
 Geologic Time is divided into four long ERA’S.
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 Precambrian, Paleozoic, Mesozoic, and Cenozoic.
 We are now in the Cenozoic Era.
 You are not responsible for the various periods of the
geologic eras.
Mass Extinctions
Mass extinction is the loss of 70% or
more of the species on earth.
 Mass extinction has occurred five times
in the history of the earth.
 Many scientists believe that we are in
the midst of the sixth and greatest mass
extinction, due to human activity.
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The fossil record supports the
Theory of Continental Drift.
The Theory of Continental Drift suggests
that the continents have moved during
earth’s history and continue to move still
at about the rate of six centimeters a
year.
 Plate techtonics explains how this
happens; plates float upon a layer of
molten rock that allow them to move.
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Origins of Life
Spontaneous Generation
Spontaneous Generation is the idea
that life can be produced from non-life.
 This was commonly believed in the
middle ages, when knowledge was
based on observation.
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Two scientists’ experiments
disproved spontaneous
generation.
Francesco Redi
and
Louis Pasteur
Redi’s Experiment
Pasteur’s Experiment
Spontaneous Generation
Disproved
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Redi disproved spontaneous generation
for large organisms.
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Pasteur disproved spontaneous
generation for microorganisms.
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Biogenesis – life can only come from
other life now the accepted theory.
How did life on Earth begin?
Hypothesis: small organic molecules formed
and then became organized into more
complex organic molecules.
 1930’s OPARIN hypothesized that the
conditions of early earth’s atmosphere and
oceans, with energy from the sun and
lightening, resulted in a primordial soup in
which chemical reactions occurred that could
have produced the molecules of life.
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Miller and Urey tested Oparin’s
Theory
Results of Miller and Urey’s
experiment
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The chemicals found in the flask showed
several kinds of amino acids, sugars, and
other small organic molecules.
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Sydney Fox went on to show that if these
molecules were heated without oxygen, the
would link and form more complex molecules.
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It is believed that these molecules became
trapped in bubbles that acted like membranes
forming structures called Protocells.
First Organisms on Earth
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Fossils of the first organisms are about
3.8 billion years old and are similar to
Archeabacteria.
 They were prokaryotes.
 They were heterotrophs, living on the
primordial soup.
 They were anaerobic, because there was no
oxygen in the atmosphere.
Autotrophic Bacteria change the
planet.
Early autotrophs were chemiosyntheic.
They used hydrogen sulfide to provide
energy to make food.
 Photosynthetic bacteria called
cyanobacteria produced oxygen that
changed the atmosphere.
 Oxygen allowed the development of the
ozone layer that protected earth from
ultraviolet radiation.
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First Eukaryotes
First eukaryotes appear around 2.1
billion years ago.
 They are thought to have developed
from the merging of prokaryotes seeking
protection from oxygen.
 The nucleus developed from the
merging of their DNA.
 Other organelles developed through
symbiotic relationships with other
ancient prokaryotes.
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Endosymbiotic Theory
Proofs of Endosymbiosis
Mitochondria and Chloroplasts
 Have separate DNA that is like prokaryote
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DNA
Can reproduce independent of the cell and
do so in the manner that prokaryotes.
They have ribosomes similar to prokaryotic
ribosomes.
They are the same size as prokaryotes.
They have two membranes: inner like
prokaryotes, outer like eukaryotes.
Charles Darwin and the Theory of
Evolution by Natural Selection
1831 Charles Darwin took a job as a
naturalist on a five year trip around the world
on the ship the Beagle.
 On his trip Darwin collected and studied
specimens from around the world.
 His trip to the Galapagos Islands led him to
consider that life has changed over time.
 He began to form his theory.
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Darwin needed more evidence.
Lyell – geologist who showed that the earth
was very old; this was needed to provide time
for evolution to occur.
 Malthus - economist who studied the human
population and proposed that the human
population was kept under control by war,
famine, and disease. Darwin used this idea
and the basis for competition and selection.
 Artificial selection – Darwin raised pigeons and
realized if he could select the best traits to
breed than nature could also – natural
selection.
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How Natural Selection Works
Organisms produce more offspring than can
survive.
 Amongst the offspring, variations exist.
 Competition for resources occurs.
 Those with the most useful variations
survive and reproduce, passing their traits
to the next generation.
 These traits become more common in the
population.
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Evidence for Evolution
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Adaptations – Organisms seem to have
variations that match their environment.
Camouflage: Organisms blend in with
their environment.
Mimicry: Harmless species looks like
another harmful species.
Direct Evidence: Physiological
Resistance
Direct Evidence can be observed.
 Antibiotic resistance in bacteria.
 Herbicide and pesticide resistance.
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Fossil Evidence
Anatomical Evidence
Homologous Structures: Structures that share a
common ancestor, but they may look different
because the organisms evolved in different
environments.
 Analogous Structures: Structures found in
organisms that do not have common ancestors,
but may look similar because evolved in similar
environments.
 Vestigial Structures: Structure that has no
function in present day organisms, but was
probably useful in the past.
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Vestigial Structures
Embryological Evidence
Biochemical Evidence
All life shares DNA as its hereditary
material.
 The closer related organisms are, the
more similar the amino acid sequences
in their proteins.
 Cytochrome c is a protein that has been
studied to show evolutionary
relationships.
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Definitions:
Population – all members of a species within
a given area.
 Species - organisms that look similar and
can breed together and produce fertile
offspring.
 Gene pool - all the alleles within a population
 Allelic frequency - percentage of any
specific allele within a population.
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Gene Pool
Genetic Equilibrium
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In genetic equilibrium the frequency of
alleles remains unchanged over
generations.
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When a population is in genetic
equilibrium, no evolution is taking place.
Mechanisms for Genetic Change
Mutation - may be good or bad; mutations
that are lethal will decrease in the
population; mutations that increase fitness
will remain.
 Genetic Drift - the random removal of
alleles from the population.
 Gene Flow - individual members of the
population leave or new individuals enter,
changing the allelic frequency.
 All of these can affect small populations
significantly.
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Genetic Drift
Gene Flow
Natural Selection
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Three types of natural selection that act on
variation:
 Stabilizing - favors the average individuals in a
population, reduces variation.
 Directional - favors one of the extreme
variations of a trait in a population.
 Disruptive - favors both extremes and tends to
eliminate the intermediates.
Speciation: the evolution of new
species
Speciation results when members of similar
populations can no longer interbreed to
produce fertile offspring within their natural
environments.
 A population may be broken into smaller ones
by physical barriers. This is called
Geographic Isolation.
 The new groups adapt to new environments
and become reproductively isolated.
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Reproductive Isolation can result
from:
Different mating seasons
 Different mating displays
 Genetic material has changed so much,
it no longer matches.
 Polyploidy - in plants, errors in meiosis
produce multiple sets of chromosomes,
preventing fertilization.
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Rates of Speciation
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Gradualism - change occurs through small
changes over long periods of time.
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Punctuated Equilibrium - change occurs in
rapid bursts when the environment changes
and is followed by periods of no change.
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Both can be supported by the fossil record.
Patterns of Evolution
Adaptive Radiation - new species develop
from a common ancestor as they adapt to
new niches in a new environment.
 Divergent Evolution - Species that were
once similar adapt to new environments and
change as they adapt. Associated with
Homologous structures.
 Convergent Evolution - Unrelated species
evolve similar traits in similar environments;
associated with Analogous structures.
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Divergent Evolution
Convergent Evolution
Adaptive Radiation