The History of Life

1
The History of Life

• Chapter 17

2
The Fossil Record

• Paleontologists study fossils creating the fossil
  record (history of life on Earth.)
• 99 of all species on Earth are Extinct.
• Fossils form in a few places in certain
  conditions. Few organisms are fossilized.
• Sedimentary rock is created by compaction
  Cementation of sediments from erosion.
• Organisms with rapid burial hard parts make the
  best fossils.

3
Formation of a Fossil
Water carries small rock particles to lakes and
seas.
Dead organisms are buried by layers of sediment,
which forms new rock.
The preserved remains may later be discovered and
studied.
4
Interpreting Fossil Evidence

• Erosion may unearth a fossil which must be
  collected before they are destroyed.
• Relative dating is determining the chronologic
  order of fossils by their position.
• Index fossils which live a short time and are
  widely dispersed are used to give dates to
  relative dating.
• Radioactive dating compares radioactive isotopes
  with specific half-lives and the daughter
  products to give an absolute date to fossils.
• A Half-life is the time an isotope requires to
  degrade into its stable daughter product.

5
Relative and Absolute Dating
Comparing Relative and Absolute Dating of Fossils
Relative Dating
Absolute Dating
Can determine Is performed by Drawbacks
6
Geologic Time Scale

• Paleontologists use the major changes in climate
  to create a geologic time scale.
• The Precambrian Era is the oldest with simple
  forms of life. Cenozoic is present.
• Eras are large chunks of geologic time
• Paleozoic- early multicellular life to large
  organisms
• Mesozoic- age of dinosaurs and early mammals
• Cenozoic- age of the mammals
• Periods are the divisions of the eras

7
Geologic Time Scale
(millions of years ago)
Era
Period
Time
(millions of years ago)
Era
Period
Time
(millions of years ago)
Era
Period
Time
Permian Carboniferous Devonian Silurian Ordovi
cian Cambrian
290  245 360290 410360 440410 505440 544
505
1.8present 651.8 14565 208145 245208
Quaternary Tertiary Cretaceous Jurassic Triass
ic
Vendian
650544
8
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
9
Formation of the Earth

• Earth began as a collection of cosmic dust.
• The debris melted and separated by density.
  Creating crust atmosphere.
• Early atmosphere contained CO2,CO, N2, H2, S,
  H2O, and hydrogen Cyanide
• About 3.8 billion years ago a solid crust,
  greenish brown oceans this is where life formed.

10
Evolution of Life on Earth
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.
11
First Organic Molecules

• Early Earth had no free O2 allow organic
  molecules to form spontaneously.
• Miller and Urey did an experiment to see if
  organic molecules would form spontaneously.
• About 3.5 billion years ago bacteria were common.
  
• Proteinoid Microspheres are bubbles of organic
  molecules which have some of the characteristics
  of life.
• Evolution of DNA probably occurred from RNA which
  can spontaneously generate.

12
Mixture of gases simulating atmospheres of early
Earth
Spark simulating lightning storms
Cold water cools chamber, causing droplets to form
Condensation chamber
Water vapor
Liquid containing amino acids and other organic
compounds
Miller-Urey Experiment
13
Free Oxygen Eukaryotes

• Mircofossils indicate little O2 in the atmosphere
  3.5 billion years ago.
• 2.2 billions years and photosynthetic bacteria
  were producing oxygen
• The oxygen combined with the iron in the
  environment.
• 2 billion years ago prokaryotes developed
  internal membranes organelles
• Eukaryotic cells arose from the endosymbiotic
  theory by Lynn Margulis in the 1960s
• Sexual reproduction increased evolution of the
  Eukaryotes allowing multicellular organisms.

14
Endosymbiotic Theory
Plants and plantlike protists
Chloroplast
Aerobic bacteria
Ancient Prokaryotes
Photosynthetic bacteria
Nuclear envelope evolving
Mitochondrion
Primitive Photosynthetic Eukaryote
Animals, fungi, and non-plantlike protists
Ancient Anaerobic Prokaryote
Primitive Aerobic Eukaryote
15
Evolution of Multicellular Life

• Precambrian was the age of bacteria.
• Paleozoic- marine organisms
• Cambrian trilobites first hard parts animals
• Ordovician/Silurian invertebrates and fishes
• Devonian Plant insect on land, age of fish
• Carboniferous/Permian amphibians and reptiles,
  ended with a Mass Extinction
• Mesozoic- age of Dinosaurs and Flowering Plants
• Triassic age of reptiles cone bearing plants
• Jurassic Dinosaurs ruled the Earth leading to
  birds.
• Cretaceous leafy trees, flowering plants, mass
  extinction
• Cenozoic- The age of mammals
• Tertiary Mammals evolved in all habitats
• Quarternary saw a cooling environment and humans

16
Patterns of Evolution

• Macroevolution is large-scale evolutionary
  patterns over long periods of time.
• Six topics in Macroevolution
• Extinction loss of a species or many species
• Adaptive Radiation one species gives rise to
  numerous different species
• Convergent Evolution unrelated organisms evolve
  similar body structures
• Coevolution Two species evolve together in
  response to one another.
• Punctuated Equilibrium long periods of no change
  then rapid evolution for a short period of time.
• Genes and Body Plans changes in developmental
  genes can greatly alter body structure.

17
Multicellular Life Evolution
Species
that are
in
under
under
form
in
in
can undergo
can undergo
can undergo
can undergo
can undergo