i. how did life begin?
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I. How Did Life Begin?. Prior to the 17 th century: 1. Spontaneous Generation : The belief that living things could come from non-living things. Francesco Redi (1668) Italian scientist. Attempted to discredit Spontaneous Generation. Experimented to prove that maggots came from flies. - PowerPoint PPT PresentationTRANSCRIPT
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I. How Did Life Begin?Prior to the 17th century:1. Spontaneous Generation:The belief that living things
could come from non-living things.
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Francesco Redi (1668) Italian
scientist Attempted to discredit Spontaneous Generation.
Experimented to prove that maggots came from flies
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Redi’s Exeriment1668 – Experiment showing how maggots come from flies
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Lazzaro Spallanzani (1700)Italian scientist Experimented with spontaneous
generation of microorganisms.1. Created meat broth2. Boiled broth to kill
microorganisms3. Capped some flasks and left
others open.
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Spallazani’s ExperimentOpponents of his study claimed that he overheated the samples…Destroying the VITAL FORCE
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Louis Pasteur (1800’s) French scientist
*The conclusions of Pasteur, brought about the theory of
BIOGENESIS – Living things come from other living things
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B. Formation Of The EarthAbout 5 billion years ago, the solar system was a mass of swirling gas and dust.
Possible result of a SUPERNOVA
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As millions of years passed, a large amount of material collapsed to the center and created the sun.
Around 4.6 billion years ago, the earth and some of the other planets were formed.
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As earth cooled, water vapor in the air condensed to form water and the first oceans. 3.8 to 3.9 billion years ago.
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C. Measuring Earth’s AgeRadiometric dating:
Estimate the age of an object by measuring its content of radioactive isotopes.
Radioactive isotopes:Unstable and “decay” over time.Half-life:The time that it takes for a
radioactive isotope to decay by one half
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D. Life On The Earth
The oldest evidence of life on the earth is found in rock estimated to be 3.5 billion years old.
The evidence shows in the form of FOSSILS.
The first fossils were referred to as MICROFOSSILS, ancient prokaryotic cells.
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1. Formation of Simple Organic Compounds
A. Primordial Soup ModelAlexander Oparin (1923) • Soviet scientist• Gases of the primitive atmosphere came together and created simple organic compounds
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When the atmosphere cooled and the rain fell, so did the compoundsOver time the compounds entered chemical reactions and proteins and other organic compounds resulted
* DID NOT run any experiments to support theory
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-In 1953, Americans, Stanley Miller and Harold Urey, set up an experiment that was based on Oparin’s theory.
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B. The Bubble ModelAmmonia and Methane were released from volcanoes into bubblesBubbles rise to the surface and burst
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Formation of protein occurred either by amino acids spontaneously combining… Or they were heated in the absence of oxygen
-Similar mechanisms may have led to the formation of carbohydrates, lipids, and nucleic acids
2. Formation of Complex Organic Compounds
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3. Concentration and Enclosure
Proteins clump together to form microscopic droplets…
A. Coacervates - droplets of different types of irregularly shaped molecules .
Includes Amino Acids and sugars
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B. Microspheres-Round, usually from one type of molecule.Separated from the environment by a membrane Chemical reactions occur here more easily than in waterCan bud off
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4. Evolution of Growth, Metabolism, and Reproduction
Coacervates and microspheres lack the complexity of living cells …
-They can grow -They can bud • They lack the ability to respond to natural selection.
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5. The Role of RNA
RIBOZYME:A special type of RNA was discovered to be able to act like an enzymeThey can replicate themselvesResearch indicates life may have started with RNA
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II. Evolution of Cellular Life
A. The First ProkaryotesScientists hypothesize that the first cells were: • Anaerobic• Heterotrophic• Prokaryotic
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B. The First EukaryotesSome early Eukaryotes may have gone through a relationship known as SYMBIOSIS.
Endosymbiosis Theory: Prokaryotic intracellular parasites evolved into various cell organellesEvidence in the mitochondria and chloroplasts
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ENDOSYMBIOSIS THEORY
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Life Invaded LandCyanobacteria: photosynthesizing organisms gave off oxygen as a waste product. (At about 2.8 billion years ago) Oxygen had two effects on the environment:1) Those organism that could bond oxygen to other compounds survived
- beginning of aerobic respiration.2) Ozone (O3) was created
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Lamarck’s ExplanationFrench scientist (1744-1829)Similar species descended from common ancestors
ACQUIRED TRAITS: explanation for species change.
• Changes arise from experiences and behavior over a lifetime
• Not determined by genes. EXAMPLES: web feet, giraffe neck, tails“USE and DISUSE”
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Charles DarwinWent to medical schoolStudy become a ministerInterested wildlife and the environmentTook a voyage on a ship, the BEAGLE, as the boats naturalist
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Darwin proposed a mechanism for evolutionNatural Selection: occurs because of ADAPTATIONSPublished a book: “On the Origin of Species” 1859, 1 year after Alfred Wallace (same basic ideas)
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Evolution by Natural Selection“Human populations are able to
increase faster than the food supply can” – Thomas Malthus 1798
Only a limited number of offspring survive to reproduce
Individuals with traits that best suit their environment are most likely to survive and reproduce
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Darwin’s Theories1. Descent with
modification:Newer life forms appearing
in the fossil record are modified versions of the old species
2. Modification by Natural Selection:
Mechanism for how evolution can occur.
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Why some organisms survive when others do not:
The environment affects individuals differentlySome traits provide an advantagePopulations ADAPT as the proportion of favorable genes increasesFITNESS: Single organisms genetic contribution to the next generation.Favorable traits provide an ADAPTIVE ADVANTAGE
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Adaptations:Inherited traits that have become
popular due to a selective advantage
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Darwin’s Theory:Based on 4 major points….1. Inherited variation exists within
the genes of every population2. Some individuals are better
suited for their environments
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3. Traits that provide an advantage are spread as individuals survive and have offspring
4. Fossils provide evidence that living species evolved from extinct species
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The Scopes Trial
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Darwin and Evolution
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Evidence of EvolutionThe Fossil Record:Fossils:Preserved or mineralized
remains or imprints of an organism that lived long ago
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Concerns with using fossils for source of evidence
The fossil record is NOT COMPLETEMany times genetic information is not available from the fossilsNot all organisms are equally likely to be fossilized
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Types of Fossils Imprints
A film of carbon remains after other elements of an organism have decayed Mold
created by the impression of a shape/track Cast
sediment fills in a cavity left by a fossil
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Fossil Video
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FOSSIL DATINGWays of
determining fossil age:
1. Position within sedimentary rock
• Look at different strata:• Deeper is older
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Dating is done by
comparing ratio of carbon 12 and carbon 14
Used to date things up to 50,000 yrs. old
2) Carbon dating
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• Isotopes• Parent • Daughter
• Half Life (yrs)
• Dating Range (yrs) • Materials
• Carbon-14• Nitrogen-
14• 5730±30 • 0100-70,000 • Anything with C
• Potassium-40
• Argon-40 Calcium-
40• 1.3 billion • 50,000-4.6 billion
• Muscovite Biotite
Hornblende Whole volcanic
rock• Uranium-238
• Uranium-235
Uranium-232
• Lead-206 • Lead-207
Lead-208
• 4.5 billion • 710 million
14 billion
• 10 million-4.6 billion •
• Zircon,U containing
• Rubidium-87
• Strontium-87
• 47 billion• 10 million-4.6
billion
• Muscovite Biotite
Potassium Feldspar
Whole metamorphic
or Igneous rock
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Evidence From Living Organisms
1) Evidence of Common Ancestry -Organisms that are similar in
structure had a common ancestor
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2. Homologous Structures vs. Analogous Structures
A. Homologous:Structures that are embryologically similar and functionally different
B. Analogous:Structures that are
embyologically different but function the same
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Homologous Structures
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4. Biochemical Comparisons:
-Examine biochemical compounds within organisms
3. Vestigial Organs:Organs that are seemingly functionless
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5. Embryological Development:
Compare organisms at various stages of development
Embryonic SimilaritiesIndicate Common ancestor