THE ORIGIN AND
EVOLUTIONARY
HISTORY
OF LIFE
CONDITIONS OF EARLY EARTH
• Age of Earth is ~4.6 billion years
• Atmosphere had little free O 2
• Included CO2, H2O, CO, H2, N2
• Maybe also NH3, H2S, CH4
REQUIREMENTS FOR CHEMICAL EVOLUTION
TO PRODUCE LIFE
• Absence of oxygen
• Energy
• Chemical building blocks
• Sufficient time
PREBIOTIC SOUP HYPOTHESIS
• Molecules formed near the Earth’s
surface
• Sugars, nucleotides, amino acids
formed spontaneously
IRON-SULFUR WORLD HYPOTHESIS
• Organic molecules formed at
hydrothermal vents on the ocean
floor
• Laboratory simulations show catalyst
effects of iron and nickel sulfides
ORIGIN OF CELLS
• Spontaneous assembly of small
organic molecules into
macromolecules
RNA WORLD
• Self-replicating RNA molecules
• Function as both enzyme and
substrate for replication
• Ribozyme is enzymatic RNA
• First step in evolution of the
DNA / RNA / protein system
DIRECTED EVOLUTION
• Large pool of RNA molecules with
different sequences
• Selected for ability to catalyze a
reaction
• Amplify / mutate / repeat
DIRECTED
EVOLUTION
• In the RNA world, ribozymes
catalyzed protein synthesis
• DNA formed from double strands of
RNA
• DNA more stable than RNA
THE FIRST CELLS
• Heterotrophs that feed on organic
molecules
• Anaerobic fermentation process to
obtain energy
AUTOTROPHS
• Selected after organic molecule food
stock became scarce
• Photosynthetic production of organic
molecules
• Cyanobacteria split water molecules
and released oxygen
FORMATION OF THE OZONE
LAYER
• Ultraviolet radiation forms O 3 from
O2 in the upper atmosphere
• Prevents UV from reaching Earth
• Decreased mutagenesis
• Enabled organisms to live in surface
waters and on land
OZONE
FORMATION
EUKARYOTES AROSE FROM PROKARYOTES
• Endosymbiont theory
• Mitochondria and chloroplasts
derived from prokaryotes
• Ingested but not digested
• Reproduced along with host cell
ENDOSYMBIONT
THEORY
GEOLOGICAL ERAS
• Paleozoic
• 543 mya - 251 mya
• Mesozoic
• 251 mya - 65 mya
• Cenozoic
• 65 mya - present
PRECAMBRIAN TIME
•
•
•
•
•
Before 543 mya
Bacteria
Protists
Fungi
Simple
multicellular
animals
CAMBRIAN EXPLOSION
• All animal phyla
established
• Many new body
plans
• Bizarre, extinct
phyla
ORDOVICIAN PERIOD
• Shallow seas
covered land
• Cephalopods
• Coral reefs
• Jawless fishes
SILURIAN PERIOD
• Jawed fishes
• Terrestrial
plants
• Air-breathing
animals
DEVONIAN PERIOD
• Bony fishes
• Amphibians
• Wingless insects
• All major plant
groups except for
flowering plants
established
CARBONIFEROUS PERIOD
• Swamp forests
• Reptiles
• Winged insects
PERMIAN PERIOD
• Therapsids
• Reptilian
ancestors of
mammals
• Seed plants
dominant
• Ended the Paleozoic
with the greatest
mass extinction
• 90% of marine
species
• 70% of land
vertebrates
MESOZOIC ERA
Divided into three
time periods
* Triassic (251-199.6
million years ago),
* Jurassic (199.6145.5 million years
ago),
* Cretaceous (145.565.5 million years
ago).
TRIASSIC PERIOD
• Thecodonts
• Ancestors of
dinosaurs and
birds
• Pleiosaurs and
ichthyosaurs
• Pterodonts
• First mammals
• Small
insectivores
JURASSIC AND CRETACEOUS PERIODS
• Saurischians
• Ancestors of
lizards
• Ornithischians
• Ancestors of birds
• Ended with mass
extinction caused by
a meteorite impact
CENOZOIC
ERA
• Began about 65
million years ago
• continues into the
present
• third
documented era
in the history of
Earth.
• Tertiary period
• Diversification
of flowering
plants, birds,
insects,
mammals
• Quaternary period
• Genus Homo
• Large mammals