BIOLOGY Chpt - 12

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BIOLOGY Chpt - 12

• History of Life on Earth

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The Theory of Spontaneous Generation

• Before the microscope, it was commonly thought
  life arose from NON-LIFE - ABIOGENESIS
• Flies came from rotting meat!
• Bacteria came from rotting broth!

• Francesco Redi - disproved flies came from
  rotting meat!
• Louis Pasteur disproved bacteria spontaneously
  arose from broth!
• BIOGENESIS- Life must arise from Life!!

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HOW DID LIFE BEGIN?

• How did life form how earth?
• 2-ways to approach this..
• Philosophy - Science

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The AGE OF THE EARTH

• Earth formed 4.5 billion years ago!
• The Earth Began as a hot molten ball of lava..
• 3.9 billion years ago water vapor began to appear
• 3.5 billion years ago-life began!

From Geology and Archeology
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A History in the Rock

• Oldest rocks - 3.9 billion years old!
• They provide us with fossils, casts, imprints,
  and specimens in amber and ice
• Most fossils occur in sedimentary rock!
• Relative dating - layers closer to the surface
  are younger than those found in deeper layers!

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Plate Tectonics and. Continental Drift

• The crust of the earth is floating on magma!
• As the magma flows, the crust is broken apart and
  squeezed together!
• These plates which hold the continents have moved
  location and thus affected life forms!
• Where these plates meet cause earthquakes, and
  volcanic activity!

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From Chemistry-Radiometric Dating ...

• TYPES
• Carbon 14 decays to Nitrogen.
• half-life 5,730 years.
• Potassium- decays to Argon then to calcium.
  half-life 1.3 -5.2 billion years
• Uranium 238 decays to lead. Dating.half life
  704 million years

• Radioisotopes-an unstable atom (extra neutrons)
• Radioactive Decay the breakdown into smaller more
  stable atoms.
• Half-life is the time needed for 1/2 of the
  substance to change!

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GEOLOGIC TIME SCALE

• The History of the Earth is divided into Four
  Eras
• Precambrian-oldest fossils of cells / water
  invertebrates
• Paleozoic -fish and plants appear
• Mesozoic- age of the Reptiles
• Cenozoic- Mammals

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Mass Extinction..

• 5 major mass extinctions
• A time when suddenly large numbers of species
  become extinct !
• Sudden Geological changes occur..
• Asteroids
• Volcanic eruptions

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If Life comes from Life. Where or How did the
first life form arise???...

• J.B. Haldane and-
• Alexander Oparin - hypothesized life began in
  the oceans from complex organic molecules!
• Harold Urey- and Stanley Miller - 1953 set up a
  test to see if the hypothesis had merit!

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The Primordial Soup !

• Stanley Millers experiment with the help of
  Harold Urey produced amino acids, sugars, and
  other organic compounds!
• Similar processes have produced ATP- energy
  carrier, and nucleic acids- the building blocks
  for DNA!
• BUT- If there was NO OZONE layer this process
  could not have happened!

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The Bubble Model

• Louis Lerman molecules for life formed within
  bubbles on the surface of the ocean.
• gases trapped in ocean vents formed bubbles
• methane and ammonia made amino acids released
  into atmosphere
• UV rays forced further molecular change
• these fell back into the ocean and repeated the
  cycle.

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Proto cells

• LIPIDS (fats) form bubbles in water.
• COACERVATES- amino acids and sugars form bubbles
  with cell membrane like structure.
• MICROSPHERES amino acid chains form bubbles
• Scientists Cech and Altman showed that RNA can
  reproduce itself and can modify its structure
  over time.

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What are these precursors of the first cells??

• Scientists disagree about the details of the
  process that led to the origin of life.
• Most scientists accept that under certain
  conditions.
• The basic molecules of life could have formed
  spontaneously through simple chemistry.

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Simple to Complex Molecules?

• There is a huge difference between simple and
  large complex molecules found in living things.
• How did amino acids link to form proteins? How do
  nucleotides come together to form long strains of
  DNA that store the instructions for making
  proteins??
• In the lab, Scientists cannot make proteins nor
  DNA form spontaneously in water.

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But get this

• Scientists have made short chains of RNA, the
  nucleic acid that helps carry out DNAs
  instructions.
• These RNA molecules have been able to form by
  themselves in water!
• Turns out that RNA molecules can act as enzymes
  to form DNA.
• Therefore, RNA was the first information storing
  molecule and it catalyzed the assembly of the
  first proteins. This molecule changed from
  generation to generation.

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Lipids

• Lipids tend to gather together in water. (Fats
  are not water soluble and are hydrophobic.)
• When some lipids are combined with other
  molecules, they form tiny droplets with a surface
  that looks like a cell membrane.

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Microspheres

• Another lab experiment shows that in water, short
  chains of amino acids can gather into tiny
  droplets called MICROSPHERES.

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Coacervates

• Another tiny droplet is made out of molecules of
  different kinds., including linked amino acids
  and sugars.

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What does all this mean?

• Scientists think that formation of microspheres
  might have been the first step of creating a
  cell. One theory says that microspheres fomed,
  lasted a while, and then dispersed.
• Over millions of years, some microspheres were
  able to survive because they blended with other
  molecules and energy. Not living cells though
  because lacked heredity!

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Origin of heredity

• Even though scientists disagree about the details
  of the origin of heredity, many agree that double
  stranded DNA evolved after RNA and that early RNA
  catalyzed the production of the first proteins.
• So we still dont know how life started naturally
  and spontaneously.

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The Evolution of PROKARYOTES

• The oldest known fossils are the PROKARYOTES.
• CYANOBACTERIA- blue green algae produced the
  OXYGEN in air !!
• Ancient prokaryotes are called ARCHAEBACTRIA.

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The first EUKARYOTE CELLS

• 1.5 Billion years ago
• first fossils of Eukaryotes!
• Eukaryotes have organelles within..(Nucleus and
  others)
• Archaebacteria-
• Cyanobacteria- developed into Chloroplasts
  and Mitochondria
• Endosymbiosis occurred..
• forming first Eukaryote cell

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The ENDOSYMBIOTANT HYPOTHESIS

• Evidence-
• Mitochondria same size as bacteria
• Chloroplasts and Mitochondria have membranes like
  bacteria
• Both have there own DNA
• Both have ribosomes like bacteria
• Both- Reproduce like bacteria

• Lynn Marguli
• Proposed prokaryote cells engulfed smaller
  cells and formed a symbiotic relationship of
  mutualism..
• where both benefit!

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Multicellularity
Protists Primative unicellular and
multicellular organisms

• Unicellular organisms unite to form
• multi-cellular
• organisms
• Specialization cells become specialized for a
  particular function

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OZONE LAYER

• As ozone formed , it allowed life to move onto
  the land.
• First Fungi as it can absorb minerals
• Plants need the minerals to carry on
  photosynthesisthey came next..
• MYCORRHIZAE- fungi and plants in a symbiotic
  relationship of Mutualism!

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Invertebrates--arrive

• Arthropods followed plants
• insects spiders- centipedes-etc
• Vertebrates
• ..fish were evolving as the
  arthropods developed on land..
• . Amphibians evolved from fish
• .Reptiles developed the egg
• .Birds developed from reptiles
• .Reptiles gave rise to the
  mammals

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