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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.

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I. How Did Life Begin?

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I how did life begin

I. How Did Life Begin?

Prior to the 17th century:

1. Spontaneous Generation:

The belief that living things could come from non-living things.

Francesco redi 1668 italian scientist

Francesco Redi (1668)Italian scientist

  • Attempted to discredit Spontaneous Generation.

  • Experimented to prove that maggots came from flies

Redi s exeriment


1668 – Experiment showing how maggots come from flies

Lazzaro spallanzani 1700

LazzaroSpallanzani (1700)

Italian scientist

Experimented with spontaneous generation of microorganisms.

1. Created meat broth

2. Boiled broth to kill microorganisms

3. Capped some flasks and left others open.

Spallazani s experiment

Spallazani’s Experiment

Opponents of his study claimed that he overheated the samples…

Destroying the VITAL FORCE

Louis pasteur 1800 s french scientist

Louis Pasteur (1800’s)French scientist

*The conclusions of Pasteur, brought about the theory of BIOGENESIS – Living things come from other living things

B formation of the earth

B. Formation Of The Earth

  • About 5 billion years ago, the solar system was a mass of swirling gas and dust.

  • Possible result of a SUPERNOVA

I how did life begin

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.

I how did life begin

As earth cooled, water vapor in the air condensed to form water and the first oceans.

3.8 to 3.9 billion years ago.

C measuring earth s age

C. Measuring Earth’s Age

Radiometric dating:

Estimate the age of an object by measuring its content of radioactive isotopes.

Radioactive isotopes:

Unstable and “decay” over time.


The time that it takes for a radioactive isotope to decay by one half

D life on the earth

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.

I how did life begin

  • A. Primordial Soup Model

  • Alexander Oparin (1923)

  • Soviet scientist

  • Gases of the primitive atmosphere came together and created simple organic compounds

1. Formation of Simple Organic Compounds

I how did life begin

  • When the atmosphere cooled and the rain fell, so did the compounds

  • Over time the compounds entered chemical reactions and proteins and other organic compounds resulted

  • * DID NOT run any experiments to support theory

I how did life begin

-In 1953, Americans, Stanley MillerandHarold Urey, set up an experiment that was based on Oparin’s theory.

B the bubble model

Ammonia and Methane were released from volcanoes into bubbles

Bubbles rise to the surface and burst

B. The Bubble Model

2 formation of complex organic compounds

2. Formation of Complex Organic Compounds

  • 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

I how did life begin

3. Concentration and Enclosure

Proteins clump together to form microscopic droplets…

  • Coacervates- droplets of different types of irregularly shaped molecules .

    Includes Amino Acids and sugars

B microspheres

B. Microspheres-

  • Round, usually from one type of molecule.

  • Separated from the environment by a membrane

  • Chemical reactions occur here more easily than in water

  • Can bud off

I how did life begin

4. Evolution of Growth, Metabolism, and Reproduction

Coacervatesand microspheres lack the complexity of living cells …

-They can grow

-They can bud

  • They lack the ability to respond to natural selection.

5 the role of rna

5. The Role of RNA


A special type of RNA was discovered to be able to act like an enzyme

They can replicate themselves

Research indicates life may have started with RNA

I how did life begin

  • II. Evolution of Cellular Life

  • A. The First Prokaryotes

    Scientists hypothesize that the first cells were:

  • Anaerobic

  • Heterotrophic

  • Prokaryotic

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B. The First Eukaryotes

  • Some early Eukaryotes may have gone through a relationship known as SYMBIOSIS.

    Endosymbiosis Theory:

  • Prokaryotic intracellular parasites evolved into various cell organelles

  • Evidence in the mitochondria and chloroplasts

Endosymbiosis theory


Life invaded land

Life Invaded Land

  • Cyanobacteria: 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

Lamarck s explanation

Lamarck’s Explanation

  • French 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”

Charles darwin

Charles Darwin

  • Went to medical school

  • Study become a minister

  • Interested wildlife and the environment

  • Took a voyage on a ship, the BEAGLE, as the boats naturalist

I how did life begin

Darwin proposed a mechanism for evolution

Natural Selection: occurs because of ADAPTATIONS

Published a book: “On the Origin of Species”1859, 1 year after Alfred Wallace (same basic ideas)

Evolution by natural selection

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

Darwin s theories

Darwin’s Theories

Descent with modification:

Newer life forms appearing in the fossil record are modified versions of the old species

Modification by Natural Selection:

Mechanism for how evolution can occur.

Why some organisms survive when others do not

Why some organisms survive when others do not:

The environment affects individuals differently

Some traits provide an advantage

Populations ADAPT as the proportion of favorable genes increases

FITNESS: Single organisms genetic contribution to the next generation.

Favorable traits provide an ADAPTIVE ADVANTAGE



Inherited traits that have become popular due to a selective advantage

Darwin s theory

Darwin’s Theory:

Based on 4 major points….

  • Inherited variation exists within the genes of every population

    2. Some individuals are better suited for their environments

I how did life begin

  • Traits that provide an advantage are spread as individuals survive and have offspring

  • Fossils provide evidence that living species evolved from extinct species

The scopes trial

The Scopes Trial

Pbs video on evolution


Darwin and evolution

Darwin and Evolution

Evidence of evolution

The Fossil Record:


Preserved or mineralized remains or imprints of an organism that lived long ago

Evidence of Evolution

Concerns with using fossils for source of evidence

Concerns with using fossils for source of evidence

  • The fossil record is NOT COMPLETE

  • Many times genetic information is not available from the fossils

  • Not all organisms are equally likely to be fossilized

Types of fossils

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

Fossil video

Fossil Video

Fossil dating


  • Ways of determining fossil age:

    1. Position within sedimentary rock

  • Look at different strata:

    • Deeper is older

2 carbon dating

2) Carbon dating

  • Dating is done by comparing ratio of carbon 12 and carbon 14

  • Used to date things up to 50,000yrs. old

I how did life begin

  • 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-40Calcium-40

  • 1.3 billion

  • 50,000-4.6 billion

  • MuscoviteBiotiteHornblendeWhole volcanic rock

  • Uranium-238

  • Uranium-235Uranium-232

  • Lead-206

  • Lead-207Lead-208

  • 4.5 billion

  • 710 million14 billion

  • 10 million-4.6 billion

  • Zircon,U containing

  • Rubidium-87

  • Strontium-87

  • 47 billion

  • 10 million-4.6 billion

  • MuscoviteBiotitePotassium FeldsparWhole metamorphicor Igneous rock

Evidence from living organisms

Evidence From Living Organisms

1) Evidence of Common Ancestry

-Organisms that are similar in structure had a common ancestor

2 homologous structures vs analogous structures

2. Homologous Structures vs. Analogous Structures

  • Homologous:

  • Structures that are embryologically similar and functionally different

    B. Analogous:

  • Structures that are

    embyologically different

    but function the same

Homologous structures

Homologous Structures

4 biochemical comparisons

-Examine biochemical compounds within organisms

3. Vestigial Organs:

Organs that are seemingly functionless

4. Biochemical Comparisons:

I how did life begin

5.Embryological Development:

Compare organisms at various stages of development




Common ancestor

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