1. The History of Life & the Origin of Species
Georgia Performance Standards:
SB5a: Trace the history of the theory of evolution.
SB5 c: Explain how fossil and biochemical evidence support the theory of evolution.
Essential Questions:
Why are there species alive now that were not found in the past fossil record?
Why is important to understand evolutionary theory?
How does fossil and biochemical evidence support the evolutionary theory?

2. 14–1 The Fossil Record 
You can study life’s history by examining fossils.
The fossil record provides evidence about the history of life on Earth.
It also shows how different groups of organisms have changed over time.
Paleontologists are scientists who collect and study fossils.

3. Fossils can show: That life on Earth has changed over time.
What past life forms were like and if they are extinct (the species died out)
The structure of the organisms
What they ate
What ate them
The environment in which they lived.

4. How Fossils Form
Either the remains of the organism or some trace of its presence must be preserved.
Most fossils form in sedimentary rock
The quality of fossil preservation varies.

5. Formation of a Fossil
Section 17-1
Dead organisms are buried by layers of sediment, which forms new rock.
Water carries small rock particles to lakes and seas.
The preserved remains may later be discovered and studied.
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7. Interpreting Fossil Evidence
Relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock
use index fossils to compare the relative ages of fossils.
Relative dating allows paleontologists to estimate a fossil’s age compared with that of other fossils.

8. Interpreting Fossil Evidence
Radioactive dating is the use of half-lives to determine the age of a sample.
A half-life is the length of time required for half of the radioactive atoms in a sample to decay.    
In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains.

9. Compare/Contrast Table
Section 17-1
Comparing Relative and Absolute Dating of Fossils
Can determine
Is performed by
Drawbacks
Relative Dating
(Absolute Dating) Radioactive Dating
Age of fossil with respect to another rock or fossil (that is, older or younger)
Age of a fossil in years
Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock
Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen
Imprecision and limitations of age data
Difficulty of radioassay laboratory methods
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10. Geologic Time Scale
Paleontologists use divisions of the geologic time scale to represent evolutionary time.
After Precambrian Time, the basic divisions of the geologic time scale are eras and periods.

11. Geologic Time Scale
Geologists divide the time between the Precambrian and the present into three eras.
Paleozoic Era
Mesozoic Era
Cenozoic Era
Eras are subdivided into periods, which range in length from tens of millions of years to less than two million years.

13. Geologic Time Scale with Key Events
Section 17-3
Era
Period
Time
(millions of years ago)
Key Events
Cenozoic
Mesozoic
Paleozoic
Precambrian
Time
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
1.8–present
65–1.8
145–65
208–145
245–208
290–245
363–290
410–363
440–410
505–440
544–505
650–544
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
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14. Chapter 14
The History of Life

15. Chapter 14
The History of Life
14.1 Fossil Evidence of Change
Plate tectonics describes the movement of several large plates that make up the surface of Earth.
These plates, some of which contain continents, move atop a partially molten layer of rock underneath them.

16. Chapter 14
The History of Life

17. Concept Map Evolution of Life Section 17-2 Go to Section:
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.
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18. Spontaneous generation is the idea that life arises from nonlife.
Chapter 14
The History of Life
14.2 The Origin of Life
Origins: Early Ideas
Spontaneous generation is the idea that life arises from nonlife.
Francesco Redi, an Italian scientist, tested the idea that flies arose spontaneously from rotting meat.

19. Chapter 14
The History of Life
14.2 The Origin of Life
The theory of biogenesis states that only living organisms can produce other living organisms.
Louis Pasteur designed an experiment to show that biogenesis was true even for microorganisms.

20. Simple organic molecule formation
Chapter 14
The History of Life
14.2 The Origin of Life
Origins: Modern Ideas
Simple organic molecule formation
The primordial soup hypothesis was an early hypothesis about the origin of life.
Organic molecules could have been synthesized from simple reactions.
UV light from the Sun and electric discharge in lightning might have been the primary energy sources.

21. Chapter 14
The History of Life
14.2 The Origin of Life
Stanley Miller and Harold Urey were the first to show that simple organic molecules could be made from inorganic compounds.
Later, scientists found that hydrogen cyanide could be formed from even simpler molecules in simulated early Earth environments.

22. Chapter 14
The History of Life

23. Life requires proteins.
Chapter 14
The History of Life
14.2 The Origin of Life
Making Proteins
Life requires proteins.
One possible mechanism for the formation of proteins would be if amino acids were bound to a clay particle.

24. Some RNA sequences appear to have changed very little through time.
Chapter 14
The History of Life
14.2 The Origin of Life
Genetic Code
Some RNA sequences appear to have changed very little through time.
Many biologists consider RNA to have been life’s first coding system.
Other researchers have proposed that clay crystals could have provided an initial template for RNA replication.

25. Scientists hypothesize that the first cells were prokaryotes.
Chapter 14
The History of Life
14.2 The Origin of Life
Cellular Evolution
Scientists hypothesize that the first cells were prokaryotes.
Many scientists think that modern prokaryotes called archaea are the closest relatives of Earth’s first cells.

26. Photosynthesizing Prokaryotes
Chapter 14
The History of Life
14.2 The Origin of Life
Photosynthesizing Prokaryotes
Archaea are autotrophic.
They do not obtain their energy from the Sun.
Archaea also do not need or produce oxygen.

27. Chapter 14
The History of Life
14.2 The Origin of Life
Many scientists think that photosynthesizing prokaryotes evolved not long after the archaea.
Prokaryotes, called cyanobacteria, have been found in rocks as old as 3.5 billion years.

28. The Endosymbiont Theory
Chapter 14
The History of Life
14.2 The Origin of Life
The Endosymbiont Theory
The ancestors of eukaryotic cells lived in association with prokaryotic cells.
The relationship between the cells became mutually beneficial, and the prokaryotic symbionts became organelles in eukaryotic cells.
This theory explains the origin of chloroplasts and mitochondria.

29. Chapter 14
The History of Life
14.2 The Origin of Life

30. Another View of Endosymbiotic Theory

31. Checkpoint Questions:
What can be learned from the fossil record?
Which type of dating provides an absolute age for a given fossil? Describe how this is done.
How are eras and periods related?
Many more fossils have been found since Darwin’s day, allowing several gaps in the fossil record to be filled. How might this information make relative dating more accurate?