1. Chapter 17:
The History of Life

2. 17-1 The Fossil Record What is a fossil?
Paleontologist: scientist who studies fossils
Fossil record: provides info about the past…
Incomplete!

3. How do fossils form? Some trace of an organism must be preserved
Sedimentary rock
Several ways:
Imprint of soft parts
Replace bone/wood/shell with minerals
“perfect preservation”
**not all living things leave fossils!**

4. Interpreting Fossil Evidence
Must find them first- earth erodes
Use pieces- rarely see whole organisms
Look for similarities/differences between fossils and current organisms
Date the fossil

5. Dating Fossils 1. relative dating- vertical order (oldest at bottom)
Index fossil: distinct fossil used to compare relative ages of fossils
2. radioactive dating- uses half life of radioactive element to determine age
Half life: length of time required for ½ radioactive atoms to decay
Ex: carbon- 14 (decays) and carbon 12 (no decay)

6. Geologic Time Scale Represents evolutionary time Worldwide studies
Use relative dating to organize
Use radioactive dating to get specific date

7. 17-2 Earth’s Early History
How did life begin? (loaded question)
Current scientific view:
Young earth struck by an object (another planet?)
Heat melted the earth- all elements rearranged
Settled by density (core, crust, atmosphere)

8. Water! 3.8 billion years ago: Earth cooled enough for water
Oceans formed- red from iron
Life began in the water!

9. How did life form? Miller and Urey
Simulated earth’s early conditions in a lab:
“Primordial soup”
Hydrogen, methane, ammonia gases
Closed off experiment to any “life”
Electric spark (to simulate lightning)
Organic compounds formed! (amino acids)
Simple compounds of primitive earth can create organic compounds

10. Free Oxygen and Life on Earth
bacteria-like organisms were first
Increase in photosynthetic bacteria:
O2 in water = ocean turns blue/green
O2 in air = sky turns blue
O2 kills many life forms
Others learn to adapt or live anaerobically

11. Origin of Eukaryotic Cells
Endosymbiotic theory: idea that eukaryotic organisms formed from a symbiosis among different prokaryotic organisms
Prokaryotes taken up by other prokaryotes
Learn to use O2= mitochondria
Photosynthetic= chloroplast

12. Increasing Diversity Among Organisms
Sexual reproduction: adds genetic variation thru gene shuffling
Multicellularity

13. Geologic Time Line Project
Work in groups of 3
You will be assigned a time period
You will have 20 min to find the following BASIC info on your period and design a mini poster for it
Period Name
Era in which it belongs
3-5 defining characteristics
A visual- make it look nice!
Be sure to include your names

14. 17-3 Evolution of Multicellular Life
Precambrian Time (88% of life on earth so far)
Anaerobic to aerobic organisms
Eukaryotes formed
Multicellular organisms
Life in sea only

15. Paleozoic Era Characterized by diversity of marine life
Cambrian Period:
“explosion” of invertebrate diversity
trilobites (arthropods)
Ordovician and Silurian Periods
Some movement to land
First vertebrate- jawless fish

16. Paleozoic Era (cont.) Devonian Period
Age of the Fishes (sharks)
First vertebrates on land (amphibians)
Carboniferous and Permian Periods
Reptiles evolve from amphibians
Mass extinction: occurs when many organisms die out at the same time

17. Mesozoic Era Characterized by dinosaurs and flowering plants
Triassic Period
Age of the reptiles
Dinosaurs
First mammals (small shrews)
Jurassic Period
When dinosaurs ruled the earth…
First bird- Archaeopteryx

18. Mesozoic Era (cont.) Cretaceous Period T-Rex ruled
Flying reptiles and birds
Shrubs and flowering plants (fruits)
Mass extinction occurs - no more dinosaurs 

19. Cenozoic Era Characterized as the age of the mammals
No more competition with dinosaurs
Adapted to land, sea and sky
Tertiary Period:
Insects, grazing animals (grass)
Quaternary Period:
Ice ages, mammoths
Early humans -> Homo sapiens

20. 17-4 Patterns of Evolution
Macroevolution: large scale patterns of processes that happen over a long period of time
Patterns/Trends:
1. extinction
2. adaptive radiation
3. convergent evolution
4. coevolution
5. punctuated equilibrium
6. developmental genes and body plans

21. 1. Extinction Remember Darwin? Fighting for resources?
Other causes include loss of an entire ecosystem (mass extinctions)
Benefits: opens up habitats for survivors
Usually see a burst of evolution/diversity

22. 2. Adaptive Radiation
Process where a single species or a small group of a species evolves into several different forms that live in different ways
Increases diversity of organisms
Ex: Darwin’s finches!

23. 3. Convergent Evolution
Process by which unrelated organisms independently evolve similarities when adapting to similar environments
Ex: penguin (bird), shark (fish) and dolphin (mammal) all develop streamline bodies and swimming appendages
Analogous structures: structures that look and function the same but have no common evolutionary history

24. 4. Coevolution
Process by which two species evolve in response to changes in each other
Ex: orchid’s spur hold nectar 40 cm down and a hawk moth has a 40 cm long feeding tube

25. 5. Punctuated Equilibrium*
Pattern of evolution in which long, stabile periods are interrupted by brief periods of more rapid change
Darwin said gradualism (slow and steady)
Rapid evolution may be due to:
Genetic drift- small pop.
Founder effect- small pop.
Mass extinction- opens new habitats

27. 6. Developmental Genes and Body Plans
Remember hox genes?
Genes cause changes in physical body plan- natural selection then acts on these changes
Ex: ancient insects= wings on all body segments and modern insects have wings on only 1 or 2 segments