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Origin Of Life
How Did Life Begin?
Earth was formed about 4.5 billion
years ago.
It was a fiery ball of molten rock
Water vapor in the atmosphere
condensed to form the oceans
Scientists think that life evolved from the
oceans and has occurred over
hundreds of millions of years.
Measuring the Earth’s Age
Scientists have been doing this for
years using radiometric dating which
is the estimation of the age of an object
by measuring the content of a certain
radioactive isotopes.
Radioisotopes are unstable isotopes
that break down and give off energy in
the form of charged particles (radiation)
This breakdown or decay results in
other smaller more stable isotopes.
For example:
The decay of potassium-40 results in
argon-40 and calcium-40
The radioisotope’s half-life is the time it
takes for one half of a given amount of
radioisotopes to decay.
Using this method scientists are able to
compute how many half-lives have
passed since a rock has formed.
Extraterrestrial Origin
Origin of life comes from outside Earth
This theory says that life might have
come here from a gravity forcing a
meteorite or asteroid carrying life to
Earth
Simple life forms like bacteria
Evidence would be meteorites and
asteroids of today
Divine Creation
The force of this theory that a God,
Gods or Goddess created life
Life forms were fish, vegetation, birds
animals, and people
Religions – Bibles – stories passed on
through the generations – ethnic or
cultural stories – debated for centuries.
Formation of the Basic
Chemicals of Life
Most scientists believe that life on earth
began as molecules of nonliving matter that
reacted chemically during the first billion
years of the earths history.
Energized by the sun and volcanic heat
simple organic molecules formed more
complex molecules that led to the formation
of the building blocks of the first cells
Big Bang Theory
“Primordial Soup” Model
Russian scientist A.I. Oparin and British
scientist J.B.S Haldane both suggested
that the Earth’s oceans contained large
amounts of organic molecules.
These organic molecules formed
spontaneously from chemical reactions
activated by solar radiation, volcanic
eruptions and lightening.
Oparin along with an American scientist
Harold Urey proposed that Earths eary
atmosphere lacked oxygen.
Instead it was rich in nitrogen, N2;
hydrogen, H2; and hydrogen containing
gases such as water vapor, H2O;
ammonia, NH3; and methane,CH4
Miller-Urey Experiment
In 1953 Stanley
Miller, working with
Urey put the gases
they proposed into
this device and
provided electrical
sparks and in a few
days they found
complex organic
molecules in his
apparatus.
These chemicals include the building
blocks of life!
Amino Acids, Fatty Acids and other
hydrocarbons
Reevaluating the Model
We now know that the molecules used
in the experiment could not have been
in abundance in early Earth.
4 billion years ago Earth did not have a
protective layer of ozone gas O3.
Without ozone protection methane and
ammonia would have been destroyed
and would make it impossible to make
key biological molecules.
Lerman’s Bubble Model
In 1986 the geophysicist Louis Lerman
suggested that the key processes took
place in bubbles in the oceans surface.
Step 1- Ammonia, methane and other
gases resulted from underwater
volcanic eruptions were trapped in
underwater bubbles
Step 2 – Inside bubbles methane and
ammonia needed to form amino acids
might have been protected from UV
radiation.
Chemical reactions occurs faster in
bubbles because of the concentration of
reactants would be greater.
Step 3 - Bubbles rose to the surface and
burst releasing organic molecules into
the air.
Step 4 – carried upward by winds the
organic molecules, exposed to UV
radiation and lightening provided energy
for further reactions.
Step 5 – more complex organic molecules
were formed from further reactions fell
back to the ocean as rain to begin other
cycles
Precursers to the First Cells
Scientists disagree about the details for
the origin of life
We can make simple organic molecules
form spontaneously but not the larger
molecules found in living cells.
However short strands of RNA have
been made to form on there own in
water.
Possible Role as a Catalysts
American scientists Thomas Cech and
Sidney Altman found that certain RNA
molecules act as enzymes
RNA was the first self-replicating,
information-storage molecule and it
catalyzed the first protiens
Such a molecule has the ability to
change from one generation to the next.
Microspheres and Coacervates
Laboratory experiments have shown
that in water lipids, when combined with
other molecules can form a droplet
whose surface resembles a cell
membrane.
Chains of amino acids can gather into
tiny droplets to form microspheres.
Coacervates, another type of droplet, is
composed of different types, including
linked amino acids and sugars
Scientist think that formation of
microspheres might have been the first
step toward cellular organization
Microspheres could not be considered
true cells unless they had the
characteristics of living things, including
heredity
Origin of Heredity
Scientists disagree about the details of
the origin of heredity, they agree that
double stranded DNA evolved after RNA
and RNA “enzymes” catalyzed the
earliest proteins.
Researchers do not yet understand how
DNA, RNA and hereditary mechanisms
first developed.
The Evolution of Cellular Life
Fossils (preserved or mineralized
remains or imprint of an organism) are
extremely rare
The oldest fossils are microscopic
photosynthetic prokaryotes called
marine cyanobacteria
Early Earth’s atmosphere had little
oxygen, marine cyanobacteria carried
out photosynthesis and released
oxygen into the oceans which
eventually was released into the air.
Today after hundreds of millions of
years the Earth’s atmosphere contains
21% oxygen.
Two Groups of Prokaryotes
Early in history prokaryotes evolved into
two groups.
Eubacteria – prokaryotes that contain a
chemical called peptidoglycan in their
cell walls. An example is E. coli
bacteria
Eubacteria include many bacteria that
cause disease and decay.
Archaebacteria are prokaryotes that
lack the peptidoglycan in their cell walls
and have unique lipids in their cell
membrane.
Chemical evidence indicates that
archaebacteria and eubacteria diverged
early
Evolution of Eukaryotes
Eukaryotes appeared about 1.5 billion
years ago.
How is a eukaryote different than a
prokaryote?
How did it evolve?
How do scientists believe that
mitochondria and chloroplasts
originated?
An American biologist Lynn Margulis
proposed a theory of Endosymbiosis
Endosymbiosis is the theory that
mitochondria are descendents of
aerobic eubacteria and chloroplast are
descendents of symbiotic
photosynthetic eubacteria
Four observations to support the idea
of endosymbiosis of mitochondria and
chloroplasts originated from bacteria:
1. Size and structure – mitochondria
are about the same size as
eubacteria. They have inner
membranes that are folded and carry
out cellular respiration. Chloroplasts
are about the same size as
cyanobacteria and have thylakoids
also where they carry out
photosynthesis.
2. Genetic material – Mitochondria and
chloroplasts both have circular DNA
that is different from that found in the
host cell but similar to chromosome
found in bacteria
3. Ribosomes – both have ribosomes
that are similar size and structure as
bacteria.
4. Reproduction – Like bacteria, mito
and chloro reproduce by binary fission
independently form the host cell
Multicellularity
Biologists classify all living things into
six broad categories called kingdoms.
The two oldest kingdoms Eubacteria
and Archaebacteria are made up of
single celled prokaryotes.
The first eukaryotic kingdom is Protista
Protists include single celled and
multicellular organisms
The oldest known fossils of multicellular
organisms are found in rocks that are
700 million years old
Among the groups of organisms that
survive today are plant-like, we know
the as seaweed; red, green and brown
algea.
Three of the multicellular groups
evolved into the kingdoms Fungi,
Plantae and Animalia
Each evolving from a protistan ancestor
Origins of Modern Organisms
Most animal phyla originated during a
short period of time ranging from 10 to
100 million years, during the late
Precambrian and early Cambrian.
This was known as the “Cambrian
Explosion”
Unusual marine animals for which there
are no living relatives.
A large collection of Cambrian fossils
were found in a geological formation in
Canada called the Burgess Shale.
This includes some of the strange
marine animals without known relatives
The Ordovician period which followed
the Cambrian period lasted from about
505 million to 438 million years ago.
Among them were trilobites are marine
arthropods that became extinct about
250 million years ago
Mass Extinctions
The fossil record shows a sudden
change at the end of the Ordovician
period
About 440 million years ago a large
percentage of organisms became
extinct.
Extinction is the death of all the
members of a species.
A mass extinction is when a large
number of species become extinct.
This was the first of five mass
extinctions that have occurred on Earth
Another mass extinction about the same
size happened about 360 million years
ago.
The third and the most devastating was
at the end of the Permian period.
About 96% of all species living at that
time became extinct.
About 35 million years later another less
devastating mass extinction took place
Although the specific reasons for these
extinctions are not known for certain
most scientists believe it is from
worldwide geological and weather
changes were the factors.
The fifth mass extinction occurred about
65 million years ago, two-thirds of all
land species including dinosaurs were
extinct.
Formation of the Ozone Layer
The sun provides life giving light and
dangerous UV radiation
In early life organisms could not leave
the water which protected them from UV
radiation.
About 3.5 million years ago, what began
adding oxygen to the Earth’s
atmosphere?
The ozone layer blocks the dangerous
UV rays of the sun
Millions of years later enough ozone
had accumulated to make Earth’s land a
safe place to live.
Plants and Fungi on Land
The first multicellular organisms that lived
on land were probably fungi living together
with plants
Each possessing something the other
needs
Plants can make nutrients from sunlight
but cannot harvest minerals needed from
bare rock
Fungi can’t make the nutrients from
sunlight but can extract nutrients from bare
rock.
Early plants and fungi had a biological
relationship called mycorrhizae
Mycorrhizae exist today between fungi
and roots of plants
The fungus provides minerals for the
plants and the plant provides minerals for
the fungus
This kind of partnership is called
mutualism, which is a relationship
between two species in which both
benefit
Plants and fungi have been living
together on land for 430 million years
Arthropods
100 million years after the first plants and
fungi covered the Earth the first animals
successfully invaded land to eat those
plants.
Arthropods have a hard outer skeleton, a
segmented body, joint limbs.
Examples: lobsters, crabs, insects and
spiders
Scorpians were the first land arthropods
The insect is a unique arthropod that
evolved from the first land dwellers and
have become the most plentiful and
diverse group of animals in Earth’s history
Insects were the first animals to have
wings
The ability to fly allows them to escape
predators, search for food, find mates and
nesting sites
This led to partnerships with flowering
plants.
The oldest know flowering plants were
about 127 million years ago
Vertebrates
A vertebrate is an animal with a
backbone
Humans and almost all animals biger
than a fist are vertebrates
About 530 million years ago the first
vertebrates were a small jawless fish
Jawed fish appeared about 430 mya
Jaws enables fish to bite and chew their
food giving them an advantage over the
fish that sucked up their food.
This made the jawed fish efficient
predators
Fish are the most successful living
vertebrate – they make up over half of
all modern vertebrates today
Amphibians
About 370 mya the first vertebrates
came out of the sea and they were
amphibians
Amphibians are smooth-skinned, fourlegged animals that include frogs,
toads, and salamanders
The most common amphibean:
U. pyours!
Structural changes in the bodies of the
amphibians occurred as they adapted to
land dwelling
They have moist breathing sacs – lungs
– allowed them to breath oxygen from
air.
Their limbs evolved from the fishes fins
The evolution of a strong support
system of bones just behind the head
made walking possible
They must lay their eggs in water or
very moist soil
Reptiles
About 340 mya reptiles evolved from
amphibians.
Snakes, lizards, turtles, and crocodiles
are examples of modern reptiles.
They have watertight skin which slows
the loss of moisture.
Reptiles lay their eggs on dry land, the
egg shells are water tight
Mammals and Birds
Birds have evolved from feathered
dinosaurs during or after the Jurassic
period
Therapsids, reptiles with complex teeth
and legs positioned beneath their body,
gave rise to mammals about the same
time as the dinosaurs, during the
Triassic period.
About 65 mya during the fifth mass
extinction most species disappeared
forever.
All the dinosaurs except for the ancestors
of the birds became extinct.
Smaller reptiles, mammals, and birds
survived
There was plenty of resources however
the climate changed, it was no longer
largely dry so reptiles’ no longer had a
great advantage.
Birds and mammals became the dominant
vertebrates
Continental drift which is the
movement of the Earth’s land masses of
the Earth’s surface through geological
time
This explains why there is a large
number of pouched mammal
(marsupials) in Australia and S. America
The continents were once connected!