The History of Life on Earth

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The History of Life on Earth
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• Rocks provide clues to the earths history

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3 Main types of rock

• Igneous Rocks that form from the cooling and
  solidification of magma
• Sedimentary Rocks that form from accumulation
  of sediment, usually in water
• Metamorphic Rocks that are changed by heat
  and/or pressure

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Lava lake in Surtsey Crater in Iceland.
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• Formation of sedimentary rock

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Gniess Example of metamorphic rock
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Fossils

• Preserved remains of ancient organisms or some
  trace of their presence
• Many found in sedimentary rock

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Index fossils
Can be used to compare relative ages of fossils
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Carbonaceous films
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Impressions imprints left by an organism
contain no organic matter
Dinosaur Ridge
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• Noahs Raven
• Footprints found by 12-year old Pliny Moody in
  Massachussetts in 1802
• People thought the prints must have been made by
  giant ravens released by Noah from the Ark

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Petrified tree at Mammoth Hot Springs in
Yellowstone National Park
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Mold of a lower Cambrian trilobite
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Cast of a Pompeii citizen killed by the 79 AD
eruption of Mt. Vesuvius.
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Cast of a dog produced by 79 AD eruption of Mt.
Vesuvius.
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Radioactive Dating

• Uses radioactive decay of elements in rocks to
  determine absolute age of rocks
• Based on half-life of a radioactive element
• Half-life length of time required for half of
  the radioactive atoms in a sample to decay
• C14 has half life of 5730 years
• K40 has half life of 1.3 billion years

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Formation of the Earth

• Pieces of cosmic debris accumulated over 100
  million years
• Collisions of early planet with other objects
  caused repeated melting of entire globe
• Densest elements formed earth core lighter
  elements formed a crust
• H, He, other light elements became atmosphere

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Formation of the Earth---early atmosphere

• Hydrogen cyanide
• Carbon dioxide
• Carbon monoxide
• Nitrogen
• Hydrogen sulfide
• Water

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The first organic molecules

• 4 bya Earths surface was cool enough for water
  to exist as a liquid
• Primitive oceans covered the earth----an abiotic
  stew of inorganic matter
• Chemical reactions caused synthesis of first
  organic molecules
• 3.8 bya first life forms appeared---single
  celled prokaryotes

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• Stanley Miller

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Miller-Urey Experiment
N2 CH4 H2 NH3
Mixture of gases simulating atmospheres of early
Earth
Spark simulating lightning storms
Cold water cools chamber, causing droplets to form
Condensation chamber
Wter vapor
Liquid containing amino acids and other organic
compounds
Amino acids Fatty acids Other hydrocarbons (no
purines, pyrimidines, sugars, nucleic acids)
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First signs of life

• Proteinoid microspheres
• Bubbles of organic compounds
• Membranes
• Store and release energy
• Acquired additional characteristics of life
• Evolution of DNA and RNA
• Small sequences of RNA formed and replicated
• DNA-directed protein synthesis

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Evolution of Life
Early Earth was hot atmosphere contained
poisonous gases.
Earth cooled and oceans condensed.
Simple organic molecules may have formed in the
oceans..
Small sequences of RNA may have formed and
replicated.
First prokaryotes may have formed when RNA or DNA
was enclosed in microspheres.
Later prokaryotes were photosynthetic and
produced oxygen.
An oxygenated atmosphere capped by the ozone
layer protected Earth.
First eukaryotes may have been communities of
prokaryotes.
Multicellular eukaryotes evolved.
Sexual reproduction increased genetic
variability, hastening evolution.
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Geologic Time Scale with Key Events
(millions of years ago)
Key Events
Era
Period
Time
Glaciations mammals increased humans Mammals
diversified grasses Aquatic reptiles
diversified flowering plants mass
extinction Dinosaurs diversified
birds Dinosaurs small mammals cone-bearing
plants Reptiles diversified seed plants mass
extinction Reptiles winged insects diversified
coal swamps Fishes diversified land vertebrates
(primitive amphibians) Land plants land animals
(arthropods) Aquatic arthropods mollusks
vertebrates (jawless fishes) Marine invertebrates
diversified most animal phyla evolved Anaerobic,
then photosynthetic prokaryotes eukaryotes, then
multicellular life
Cenozoic Mesozoic Paleozoic Precambrian Ti
me
Quaternary Tertiary Cretaceous Jurassic Triassic P
ermian Carboniferous Devonian Silurian Ordovician
Cambrian
1.8present 651.8 14565 208145 245208 290245
363290 410363 440410 505440 544505 650544
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First forms of life 3.5 bya

• Cyanobacteria
• Fossil colonies
• called stromatolites
• are 3.5 billion years
• old
• Created atmospheric O2 as byproduct of
  photosynthesis

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• Sexual reproduction increases the chance of
  evolutionary change due to natural selection
• Appearance of multicellular organisms increased
  diversity of life

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Vendotaenid algae from Namibia (2.5 245
mya) One of the first eukaryotes, first
multicellular organisms
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Origin of Eukaryotic Cells
Endosymbiotic Theory
Chloroplast
Plants and plantlike protists
Aerobic bacteria
Ancient Prokaryotes
Photosynthetic bacteria
Nuclear envelope evolving
Mitochondrion
Primitive Aerobic Eukaryote
Animals, fungi, and non-plantlike protists
Ancient Anaerobic Prokaryote
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Lynn Margulis
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Cambrian Period, 540-500 mya
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Ordovician Period
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Silurian Period 425-408 MYA
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Devonian The age of Fishes -- 390 mya
Map of the world during the Devonian period
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Devonian Period, 408-362 MYA
2nd mass extinction 360 mya
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Carboniferous Period, 362-290 MYA
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Permian Period, 290-245 MYA 3rd mass extinction
245 mya
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Triassic Period, 245-208 MYA
4th mass extinction 210 mya
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Jurassic Period, 208-145 MYA
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Jurassic Period, 208-145 MYA
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Cretaceous Period, 145-65 MYA
5th mass extinction 65 mya
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Tertiary Period, 65-1.64 MYA
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Tertiary Period, 65-1.64 MYA --- Hominids in
Africa
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Quaternary Period, 1.64 MYA - present
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1.64 mya - present Homo sapiens
Quaternary Period, Neanderthals

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Radiometric Dating Problems

• C-14 has a half life of 5770 years. (This means
  that it takes 5770 years for half of the
  radioactive C-14 in a sample to decay into other
  substances)
• If a fossil is 11540 years old, then how many
  half lives have passed?
• K-40 has a half life of 1.3 billion years (1300
  million years).
• If a fossil is found having ½ of the initial
  amount of K-40, how many half lives have passed?
• How old is the fossil?
• If a fossil is found having 1/16 of the initial
  amount of K-40, how many half lives have passed?

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Radiometric Dating Problems

• C-14 has a half life of 5770 years. (This
  means that it takes 5770 years for half of the
  radioactive C-14 in a sample to decay into other
  substances)
• If a fossil is 11540 years old, then how many
  half lives have passed?
• 11570/5770 2 2
  half lives
• K-40 has a half life of 1.3 billion years
  (1300 million years).
• If a fossil is found having ½ of the initial
  amount of K-40, how many half lives have passed?
  
• Since half of the K40 has
  decayed, this means 1 half life has passed
• 3. How old is the fossil?
• Since the half life of K40 is
  1.3BY, this fossil is 1.3 billion years old
• 4. If a fossil is found having 1/16 of the
  initial amount of K-40, how many half lives have
  passed?

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Radiometric Dating Problems

• 4. If a fossil is found having 1/16 of the
  initial amount of K-40, how many half lives
  have passed?
• after 1 half life..1/2 is left
• after 2 half lives..1/4 is left
• after 3 half lives..1/8 is left
• after 4 half lives..1/16 is left
• after 5 half lives..1/32 is left
• So, 4 half lives have passed for this
  fossil

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THE END