Chapter 12 History of Life

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Chapter 12 History of Life
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12-1 How Did Life Begin

• How old is the Earth?
• 4.5 to Billion Year Old!
• How do we know?

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Radiometric Dating

• Calculating the age of an object by measuring the
  proportions of the radioactive isotopes of
  certain elements
• Radioisotopes are unstable elements
• They decay, or break apart

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• We measure decay using the half-life of the
  element
• Half-life means how long it takes for half the
  atoms of a given radioisotope to decay
• Different half-life for different elements

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Life From ??

• Life on planet Earth came from two possible
  sources.
• Most likely is Spontaneous Origin, life
  developing from organic molecules reacting with
  the environment
• Where do we get organic molecules?

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• Deep Sea Hydrothermal Vents
• Extraterrestrial Seeding
• Frozen Ocean Theory

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Conditions of Early Earth
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THE EARLY ATMOSPHERE

• Possible gasses H2O, NH3, CH4, H2, CO2.
• Ammonia would have broken down
• 2NH3 into N2 3H2 (escaped to space)
• Final content was probably H2O vapor, CO2 and CO,
  N2 (80).
• NO OXYGEN

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REQUIREMENTS FOR LIFE

• Lack of oxygen (reducing atmosphere).
• Appropriate chemicals (water, organic and
  inorganic molecules)
• Sources of energy (U.V., heat, lightning)
• Great amounts of time
• NO ENZYMES WERE PRESENT
• REACTIONS WERE SLOW

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Oparin and Haldane 1920s

• Hypothesized steps of chemical evolution from
  primitive earth conditions.
• Led to the Primordial Soup Model

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Miller and Urey, 1953

• Tested Oparin and Haldanes hypothesis.
• Experiment - to duplicate primitive earth
  conditions in the lab.

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Results

• Organic monomers formed including Amino Acids.

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Problems With The Model

• No ozone to protect the gases in the atmosphere
• UV radiation would have destroyed ammonia and
  methane

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Bubble Model

• Louis Lerman suggested that the key process to
  form organic chemicals occurred at the oceans
  surface

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What About Genetic Information?
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Genetic Information

• DNA ? RNA ? Protein
• Too complex for early life.
• Other forms of genetic information?

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RNA Hypothesis

• RNA as early genetic information.

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Rationale

• RNA polymerizes easily.
• RNA can replicate itself.
• RNA can catalyze reactions including protein
  synthesis.

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What About Cell Membranes?

• Short chains of amino acids can lead to
  microspheres

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Coacervates

• Colloidal droplets of proteins, nucleic acids and
  sugars surround by a water shell.
• Will form spontaneously from abiotically produced
  organic compounds.

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12-2 Development of Life

• Oldest fossils are 3.5 Billion Years Old
• They are prokaryotes
• First prokaryotes were heterotrphs then
  autotrophs
• Cyanobacteria were among the first photosynthetic
  bacteria
• Responsible for free oxygen in the atmosphere

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• Eubacteria are prokaryotes that contain
  peptidoglycan
• Archeabacteria are prokaryotes that do not
  contain peptidoglycan
• Evidence indicates that archeabacteria were the
  1st group to evolve

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1st Eukaryotes

• Appear about 1.5 Billion Years Ago
• Mitochondria and Chloroplast appearance explained
  by endosymbiosis
• These organelles are descended from aerobic,
  symbiotic eubacteria
• Both organelles have their own DNA

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Multicellular Forms of Life

• Have developed many times
• Life grouped into 6 Kingdoms
• Eubacteria and Archeabacteria are single celled
• Fungi, Plants, Protists, and Animals have
  multicellular organisms

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Cambrian Explosion

• When the most of the current body plans 1st
  appear in the fossil record
• Most famous fossil find from this time period was
  the Burgess Shale

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Mass Extinctions

• Impact life because it reduces the amount of
  competition for resources
• Allows for adaptive radiation to occur
• Almost every time period has one!

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12-3 Progression of Life

• Once the ozone layer formed, life could invade
  the land
• Ozone began to form around 2.5 BYA
• Is formed when oxygen gas (O2) becomes O3 from
  the radiation of the sun

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• 1st multicellular land organisms were plants and
  fungi (Around 430 MYA)
• Created a mutualistic realationship
• Means both benefit
• Called mycorrhizae

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• Arthropods were the first animals to invade land
  (After the plants and fungi)
• Arthropods have a hard exoskeleton and jointed
  limbs
• Examples include lobsters, crabs, insects,
  arachnids, scorpions

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• Vertebrates followed arthropods
• Vertebrates have a backbone
• First ones were small, jawless fish in the oceans
• Then came the jawed fishes

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• Amphibians were the 1st land vertebrates
• Could breath air
• Had better adaptations for thriving on land than
  fish

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• Reptiles evolved from amphibians
• Even more adapted to life on land
• Had water tight skin, and shelled eggs

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• Mammals and Birds evolved from reptiles
• Better adapted to the changes in the climate at
  the end of the Cretaceous

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Time Periods in Order

• Cambrian (Oldest)
• Ordovician
• Silurian
• Devonian
• Carboniferous
• Permian

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• Triassic
• Jurassic
• Cretaceous
• Tertiary
• Quaternary (Present)