Scientists thought the earth was a molten body 4.6 billion years ago

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Scientists thought the earth was a molten body
4.6 billion years ago
gravity
gravity
Atmosphere Water Vapor CO2 SO2 CO H2S HCN N
2 H2
heat
Crust on surface
As cooled, liquid on surface
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Earliest clue of life about 3.5 billion years ago
Fossil
Preserved evidence of an organism
Must be buried quickly in sediment occurs more
in water
Fossils cant be formed in rock made under high
heat (igneous rock) or high heat and pressure
(metamorphic rock)
Fossil record like swiss cheese a lot of holes
in it
99 of species now extinct and only a small are
preserved
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Types of Fossils
1. Trace
Indirect evidence Ex. Footprints, burrows,
feces
2. Molds Casts
Mold impression Cast mold filled with
sediment
3. Replacement
Original material replaced with mineral crystals
4. Petrified or premineralized
Empty pores filled by minerals
5. Amber
Tree sap traps entire organism
6. Original material
Mummification or frozen specimens
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Paleontologist
Studies fossils
Fossil Dating
1. Relative dating
Compare layer to other layers
youngest
Law of superposition
older
Use decay of radioactive isotopes to measure age
of rock
2. Radiometric dating
Isotope
Half life
Must know 1. ½ life of isotope 2. Relative
amounts of radioactive isotope and its decay
product.
Different substance
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Example
4510 million years
Uranium 238
Lead 206
Isotopes only found in igneous or metamorphic rock
Use Carbon 14 to date organic substances
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Geologic Time Scale
Eon
Era
Periods
Epoch
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Spontaneous Generation
Life arises from non-life
Ex. Mud becomes worms
Flies
1668 Francesco Redi
Flies
meat
meat
No Maggots
Maggots
1800s Louis Pasteur
Proved Biogensis for microorganisms life comes
from life
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Simpler organic molecules made complex organic
molecules
Developed simple metabolic pathways to synthesize
or break down substances.
1920s Alexander Oparin
Suggested gases stimulated by UV from sun and
electric discharge from lightening made organic
substances in primordial soup
1953 Stanley Miller and Harold Urey
Showed inorganic molecules could make simple
organic molecules produced amino acids
Since, other scientists have made sugars and
nucleotides
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Amino acids needed to bond to make proteins
Think amino acids joined to clay to provide
framework
Think RNA was the first coding system
Ribozymes are RNA that act like enzymes could
have carried out early life processes
Next, trying to figure out how membranes could
have been formed
In 2004, fossilized microbes were discovered in
volcanic rock 3.5 billion years old.
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1st Cells think
Prokaryotes Archaebacteria (extremists)
Archae could obtain energy from inorganic
molecules
Next
Photosynthesizing prokaryote - cyanobacteria
Made Oxygen and created the ozone layer
Eukaryotic cells appeared 1.8 billion years ago
1966 Lynn Margulis proposed endosymbiont
theory
Prokaryotic cells became organelles in eukaryotic
cells
Mitochondria and chloroplasts

• Contain their own DNA arranged in a circular
  pattern
• Have ribosomes that resemble prokaryotic
  ribosomes
• Reproduce by fission independent from rest of
  cell