1. Copyright Pearson Prentice Hall
Biology
Copyright Pearson Prentice Hall

2. Copyright Pearson Prentice Hall
17-1 The Fossil Record
Photo credit: Jackie Beckett/American Museum of Natural History
Copyright Pearson Prentice Hall

3. Fossils and Ancient Life
What is the fossil record?
Copyright Pearson Prentice Hall

4. Fossils and Ancient Life
The fossil record provides evidence about the history of life on Earth. It also shows how different groups of organisms, including species, have changed over time.
Could be eggs, footprints, body parts etc
Fossils and Ancient Life
Copyright Pearson Prentice Hall

5. Fossils and Ancient Life
The fossil record provides incomplete information about the history of life.
Over 99% of all species that have lived on Earth have become extinct, which means that the species has died out.
Those species that still exist are referred to as being extant.
Copyright Pearson Prentice Hall

6. Copyright Pearson Prentice Hall
How Fossils Form
How Fossils Form
Most fossils form in sedimentary rock.
Sedimentary rock forms when exposure to the elements breaks down existing rock into small particles of sand, silt, and clay.
Copyright Pearson Prentice Hall

7. Copyright Pearson Prentice Hall
How Fossils Form
Fossil Formation
Water carries small rock particles to lakes and seas.
The fossil record provides evidence about the history of life on Earth. Most fossils are formed in sedimentary rock.
Copyright Pearson Prentice Hall

8. Copyright Pearson Prentice Hall
How Fossils Form
Dead organisms are buried by layers of sediment, which forms new rock.
The fossil record provides evidence about the history of life on Earth. Most fossils are formed in sedimentary rock.
Copyright Pearson Prentice Hall

9. Copyright Pearson Prentice Hall
How Fossils Form
The preserved remains may be later discovered and studied.
The fossil record provides evidence about the history of life on Earth. Most fossil formed in sedimentary rock.
Copyright Pearson Prentice Hall

10. Interpreting Fossil Evidence
Paleontologists determine the age of fossils using relative dating or radioactive dating.
Copyright Pearson Prentice Hall

11. Interpreting Fossil Evidence
Relative Dating
In relative dating, the age of a fossil is determined by comparing its placement with that of fossils in other layers of rock.
Rock layers form in order by age—the oldest on the bottom, with more recent layers on top.
Copyright Pearson Prentice Hall

12. Interpreting Fossil Evidence
Relative Dating
In relative dating, a paleontologist estimates a fossil’s age in comparison with that of other fossils. Each of these fossils is an index fossil. It enables scientists to date the rock layer in which it is found. Scientists can also use index fossils to date rocks from different locations.
Photo credit: l. ©David Hanson/Stone; r. ©CORBIS
Copyright Pearson Prentice Hall

13. Interpreting Fossil Evidence
Index fossils are used to compare the relative ages of fossils.
An index fossil is a species that is recognizable and that existed for a short period but had a wide geographic range.
Copyright Pearson Prentice Hall

14. Interpreting Fossil Evidence
Radioactive Dating 
Scientists use radioactive decay to assign an absolute age to rocks.
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.
Copyright Pearson Prentice Hall

15. Interpreting Fossil Evidence
Radioactive dating involves measuring the amounts of radioactive isotopes in a sample to determine its actual age. Such measurements enable scientists to determine the absolute age of rocks and the fossils they contain.
Copyright Pearson Prentice Hall

16. Copyright Pearson Prentice Hall
The basic divisions of the geologic time scale are eras and periods.
Geologic Time Scale
Copyright Pearson Prentice Hall

17. Copyright Pearson Prentice Hall

18. Copyright Pearson Prentice Hall
Extinction Rate
Millions of years ago
600
500
400
300
200
100
Permian mass
extinction 80 60 40 20
Extinction rate
Cretaceous
mass extinction
2,500
2,000
1,500
1,000
Neogene
Proterozoic eon
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Triassic
Jurassic
Paleogene
Paleozoic
Mesozoic
Ceno-
zoic
Number of families ( )
Extinction rate (
Number of
taxonomic
families
Copyright Pearson Prentice Hall

19. Copyright Pearson Prentice Hall
Geologic Time Scale
Geologic time begins with Precambrian Time, which covers about 88% of Earth’s history.
The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.
Vendian
650–544
Copyright Pearson Prentice Hall

20. Copyright Pearson Prentice Hall
Geologic Time Scale
Eras 
Geologists divide the time between Precambrian time and the present into three eras:
Paleozoic Era
Mesozoic Era
Cenozoic Era
Copyright Pearson Prentice Hall

21. Copyright Pearson Prentice Hall
Geologic Time Scale
Permian
290–245
Carboniferous
360–290
Devonian
410–360
Silurian
440–410
The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.
Ordovician
505–440
Cambrian
544–505
Copyright Pearson Prentice Hall

22. Copyright Pearson Prentice Hall
Geologic Time Scale
Cretaceous
145–65
Jurassic
208–145
The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.
Triassic
245–208
Copyright Pearson Prentice Hall

23. Copyright Pearson Prentice Hall
Geologic Time Scale
The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.
Copyright Pearson Prentice Hall

24. Copyright Pearson Prentice Hall
Geologic Time Scale
Clock Model of Earth’s History
First humans
Radiation of mammals
First land plants
First prokaryotes
First multicellular organisms
Cenozoic Era Mesozoic Era Paleozoic Era Precambrian Time
Earth’s history is often compared to a familiar measurement, such as the twelve hours between noon and midnight. In such a comparison, notice that Precambrian Time lasts from noon until after 10:30 pm.
First eukaryotes
Accumulation of
atmospheric
oxygen
Copyright Pearson Prentice Hall

25. Copyright Pearson Prentice Hall
17-2 Earth's Early History
Photo credit: Jackie Beckett/American Museum of Natural History
Copyright Pearson Prentice Hall

26. Copyright Pearson Prentice Hall
17-2 Earth's Early History
What prevents organic molecules from forming on their own and remaining intact today? (424)
What are the characteristics of earth before oceans formed? (423)
The first organisms on Earth were most like todays? (426)
Why did the development of sexual reproduction speed up the process of evolution? (428)
Two gasses that probably existed in Earths early atmosphere are? (423)
Photo credit: Jackie Beckett/American Museum of Natural History
Copyright Pearson Prentice Hall

27. Copyright Pearson Prentice Hall
17-2 Earth's Early History
What prevents organic molecules from forming on their own and remaining intact today? (424) Atmospheric oxygen is too reactive
What are the characteristics of earth before oceans formed? (423) volcanic activity, atmosphere of poisonous gas
The first organisms on Earth were most like todays? (426) bacteria
Why did the development of sexual reproduction speed up the process of evolution? (428) it increases genetic variety
Two gasses that probably existed in Earths early atmosphere are? (423) hydrogen cyanide and carbon monoxide
Photo credit: Jackie Beckett/American Museum of Natural History
Copyright Pearson Prentice Hall