Earth formed about 4.6 billion years ago with a harsh atmosphere containing no oxygen. The earliest evidence of life on Earth is microscopic fossils that are approximately 3.5 billion years old. It is proposed that early life began through chemical evolution, with organic compounds assembling into early bacterial cells near hydrothermal vents. Photosynthesis evolved in cyanobacteria which increased oxygen levels in the atmosphere.

2.  Earth is estimated to be about 4.6 billion
years old.
 Atmosphere was very harsh.
 Very hot.
 Lot’s of water vapor in the atmosphere.
 Volcanic activity.
 NO BREATHABLE OXYGEN GAS!
 Carbon dioxide, ammonia, hydrogen gas,
were present
 We needed to find earliest evidence of
life for clues to what it was

3. Origin of Life
 Scientists had hard time
finding ancient evidence of
life
 45 years ago we found out
why.
 Most ancient life was
Cyanobacteria fossil about
microscopic=microfossils 1,000,000,000 (1 billion)
years old found in stromatolites
 Oldest microfossil3.5
billion years old
 1st organisms were bacteria

4. How did life begin?
 Extraterrestrial origin
 Creation ( ID )—”divine forces”
 From non-living matter “Chemical Evolution”
 Main proposal as to how this happened
Organic compounds (microspheres)
Assemble to create 1st bacterial cell
Some bacterial cells became organelles of
others to form eukaryotic cells
Eukaryotic cells join to form multicellular
organisms

5. Origin of Life’s Chemicals
 Miller-Urey
 Experiment that
recreated atmosphere
of early Earth
 Hypothesis: Can
organic compounds
form in early Earth
conditions?
 Results: amino acids,
nucleotides, lipids,
carbohydrate pieces
out

6. Self Assembly
 Molecules can
spontaneously form into
droplets—oil and water
 Protein + water =
“microspheres”
 Solution with lipids will self
assemble into a lipid bilayer
 Droplets can enclose watery
solution different from
surroundings
 BOTH SMALL SPHERES
RESEMBLE CELL
MEMBRANES!

7. 1 genetic material- RNA
st
 Earth’s early surface was inhospitable
due to immense UV radiation
 Deep sea vents on the sea floor may
have provided sheltered location for
life.
 RNA can form in labs under conditions
similar to areas near deep sea vents
 Oldest living prokaryotes found there
today…

8. Road to Modern Organisms
 1st
life was bacteria unicellular prokaryotes
 Photosynthesis changed Earth’s
atmosphere released O2 - cyanobacteria!!!!
 2nd was unicellular eukaryotes
Endosymbiotic Theory
 Then multicellular organisms

9. GENERAL EVOLUTION TIMELINE
 EARTH
 MOLECULES
 PROKARYOTES
 SINGLE-CELLED EUKARYOTES
 MULTICELLULAR ORGANISMS
 MARINE INVERTEBRATES
 MARINE VERTEBRATES
 LAND PLANTS
 LAND VERTEBRATES
 REPTILES
 GYMNOSPERMS--EVERGREENS
 MAMMALS
 DINOSAURS
 BIRDS
 ANGIOSPERMS-- FLOWERING PLANTS
 DINOSAUR EXTINCTION
 EARLY PRIMATES
 ANTHROPOIDS
 HUMANS

10.  Timeline of Life
 Earth formation
• 4500 million (4.5 billion) years ago
 Miller’s molecules
• 4000 million (4.0 billion) years ago
• amino acids
• proteins
• carbohydrates
• nucleic acids
• mass extinction

11.  First life on Earth
• 3500 million years ago
• bacterial (prokaryotic) cell
 Evolution of cyanobacteria
• Blue-green bacteria
• Photosynthesis
• Oxygen production!
 First single eukaryotic cells
• 2200 million years ago
• Organelles such as mitochondria and chloroplasts
made of prokaryotic cells. Have their own DNA

12.  First multicellular organisms
• 2000 million years ago
• eukaryotic algae
• OXYGEN IN ATMOSPHERE to form protective
ozone layer

O3

absorbs UV light

protects DNA from mutation

allowed life on land
 First invertebrate marine animals
• 500 million years ago
• Jellyfish

13.  First marine vertebrates and land plants
• 450 million years ago
• Jawless fish
• Giant ferns
 First land vertebrates
• 340 million years ago
• amphibians—toads frogs
• lungs  blood flow from heart to lungs
• lose water from their skin so must stay moist
 First reptiles and insects
• 300 million years ago
• snakes, crocodiles, turtles, lizards
• skin watertight, so could live out of water
• spiders

14.  First gymnosperms
• 290 million years ago
• naked seeds
• Evergreen trees
 First mammal like reptiles
• 240 million years ago
• 4 chambered heart
• milk
• fur

15.  First dinosaurs
• 220 million years ago
• Dinosaurs dominated in the Jurassic period
 First birds evolve
• 180 million years ago
• reptiles found on land, sea and in air
• Archeopteryx
 Flowering plants appear
• 120 million years ago
• angiosperms
 Dinosaur extinction
• 65 million years ago

16.  Very early primates
• 64 million years ago
• Order of mammals that apes, monkeys, and
humans belong to.
 Anthropoids evolve
• 35 million years ago
• Day active-primates
• Animals with five flexible fingers
• Monkeys, apes, and humans

17.  Lucy fossil
• 4 million years ago
• earliest hominid—common ancestor to humans
and apes (gorillas, orangutans, and chimps)
• walked upright, small skull, teeth intermediate
between humans and apes
 Homo sapiens
• 0.1 million years ago (100,000 years ago)
• Human species
• Direct ancestor is Homo erectus