1. HISTORY OF LIFE ON EARTH

2. EARTH’S HISTORY Earth’s age: - about 4.6 billion years old (big bang)
First life forms appeared ~3.5 billion years ago
How did life arise?
Small organic molecules were synthesized (amino acids, N bases)
Small molecules  macromolecules (proteins, nucleic acids)
Packaged into protocells (membrane-containing droplets with internal chemistry different from surroundings)
Origin of self-replicating molecules allow for inheritance
“RNA World”: 1st genetic material most likely RNA
First catalysts: ribozymes (RNA)

3. Models of Formation of Life
Reducing Atmosphere /Primordial Soup Model
1920’s: Oparin (Russian), Haldane (British)
Atmosphere made of H2O vapor, NH3, CH4, and CO (no free O2- atmosphere couldn’t sustain life )
Abiotic synthesis of organic molecules from inorganic molecules
- Molecules pushed together by energy of sun and lightening
- Molecules split, and formed new organic molecules (a.a., nucleic acids)
Organic molecules formed under conditions of volcanic eruptions

4. 1953: Miller, Urey
Tested primordial soup model by placing same molecules in chamber
with electric sparks.
After few days found organic molecules were formed.

5. Murchison Metiorite Hypothesis
Murchison Metiorite (4.5 BYO) fell to Earth in 1969
Carbon
80+ amino acids
Lipids
Simple sugars
N bases (uracil)

6. Origin of Cells (Protobionts)
Protocells
Led to the current membrane bound system
Bubbles - separate inside from outside
- show metabolism & reproduction (self replicating)
* Montmorillonite clay increases vesicle formation*
thought to have been common on Earth

7. RNA is likely first genetic material
Roles of RNA
Ribozymes- type of RNA found in some unicellular eukarytoes
- able to act as an enzyme and replicate itself
(Thomas Cech- early 1980’s)
Self replicating RNA- new studies indicate that life may have started this way
- it would:
a. have heredity: be able to provide hereditary
information that cell like structures lack
b. be able to respond to natural selection and evolve

8. Fossil Record Documents History of Life
Sedimentary rock (layers called strata)
Mineralized (hard body structures)
Organic – rare in fossils but found in amber, frozen, tar pits
Incomplete record – many organisms not preserved, fossils destroyed, or not yet found

10. Determining the Age of the Earth
Relative Dating
Radiometric Dating
Uses order of rock strata to determine relative age of fossils
Measure decay of radioactive isotopes present in layers where fossils are found

11. Radiometric Dating
radioisotope: unstable isotopes of certain elements that break down (decay) and lose neutrons. As they break down, they release charged particles (electrons) in the form of radioactivity
decay: changing of one element into another as elec. are given off
- half life: time period in which half the initial number of atoms decay into atoms of the element they change into (non radioactive)

12. By knowing the time of the half life and how many have passed, number of years can be calculated by counting number of remaining “parent” isotope atoms left in sample and number of accumulating “daughter isotopes” formed. Limitation: 75,000 years. Scientists then use relative dating.

13. Key Events in Origin of Life
Geologic Time Scsle
Eon  Era  Period  Epoch
(longest to shortest)
Archaean/Proterozoic Eons (4 b years duration)
Pharaerozoic Era
(.5 b years duration)
Animals on Earth

14. Key Events in Origin of Life
Life originated bya

15. Key Events in Origin of Life
O2 accumulates in atmosphere ( bya) Humans (200K)

16. First Unicellular Organisms (2.1 bya)
Stromatolites : fossilized layered rocks of prokaryotes that resemble modern microbial colonies

17. Development of Complex Organisms
Prokaryotes
archaebacteria: - thrived under harsh environmental conditions
- most likely first organisms on earth
- probably anaerobes (very little oxygen present)
- chemiautotrophs: CO2 serves as carbon source to make organic molecules
- evidence indicates eukaryotes evolved from these
- cyanobacteria: more modern photosynthetic bacteria that
released oxygen into the atmosphere (

18. Evidence of Oxygen Atmosphere
Oxygen begins to accumulate 2.7 bya
ancient cyanobacteria and photosynthetic algae
reducing  oxidizing atmosphere
- evidence in banded iron in rocks
- rusting makes aerobic respiration possible

19. First Eukaryotes (2.1 bya)
Endosymbiont theory: mutually successful beneficial relationship between two organisms
Mitochondria & plastids (chloroplasts) formed from small prokaryotes living in larger cells

20. mitochondria- evolved from
non-photosynthetic bacteria
invading bacteria
chloroplasts- evolved from photosynthetic bacteria invading bacteria (closely related to cyanobacteria)
- both have own DNA (plasmids)
- able to replicate on their own
- replication by binary fission
- ribosomes (similar to prokaryote ribo.)
- enzymes similar to living prokaryotes
- two membranes

21. Multicellular Eukaryotes (1.5 bya)
Snowball Earth hypothesis
Most Earth landmasses covered with ice
Most life near deep sea vents, hot springs, equator
Cambrian Explosion (40 m years)
Diversification of Animals
within 10–20 million years most of the
major phyla of animals appear in
fossil record

22. Colonization of Land (500 mya)
Pangaea: Supercontinent
Formed 250 mya
Continental drift explains many biogeographic puzzles
Arrows show direction of movement

23. Major periods in Earth’s history end with mass extinctions and new ones begin with adaptive radiations. - at least 50% of marine species become extinct - mass extinctions increase diversity of life

24. Permian mass extinction (96% of marine animal species )
- mass volcanic eruptions (Siberia)
- global warming, ocean anoxia, destruction of ozone
Cretaceous mass extinction (50% marine sp., dinosaurs)
- asteroid or meteor (Mexico)

25. Major events during each Era
Precambrian: microscopic fossils (stromatolites) Photosynthesis, atmospheric O2 Eukaryotes (endosymbiont theory) Paleozoic: Cambrian Explosion Plants invade land, many animals appear Permian Extinction (-96% species) Mesozoic: “Age of Reptiles”, dinosaur, plants Formation of Pangaea supercontinent Cretaceous Extinction – asteroid off Mexico’s coast Cenozoic: Primates * All end with major extinction & start with adaptive radiation*

26. Consequences of Mass Extinctions
Reduction of thriving ecological communities
Long time periods for recovery of life
Changes is type of remaining organisms
Pave way for adaptive radiations
- adaptations in new species fill different vacant niches
Worldwide Adaptive Radiations

27. - a few organisms make it to a new distant location
Regional Adaptive Radiations
- a few organisms make it to a new distant location
- different island conditions increase evolutionary divergence by natural selection

28. Effects of Developmental Genes Evolution of new body forms results from changes in DNA or regulation of developmental genes

29. Changes in Rate and Timing
Heterochrony: evolutionary change in rate of developmental events
Rapid reproductive organ development Salamander adult retains juvenile
structures in ancestral specie

30. Changes in Spatial Pattern and Genes
Homeotic genes: master regulatory genes determine location and organization of body parts
ex: Hox genes: tells cells to develop intro appropriate structures for body location
limb development changes in insect body plan
Ubx (suppresses leg development) expressed in abdomen vs main body

31. Changes in Gene Regulation
Caused by mutations in regulation of
developmental genes
What caused loss of spines in stickleback fish?
PTX1 expression in ventral spine PTX1 expression in mouth region

32. Evolutionary Trends
Evolution is the result of the interactions between organisms and their current environments. If environmental conditions change, an evolutionary trend may cease or even reverse itself.