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Copyright Pearson Prentice Hall
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Outine 17-1: The Fossil Record
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17-1 The Fossil Record Fossils and Ancient Life
I. Fossils and Ancient Life
A. Paleontologists are scientists who collect and study fossils.
B. Fossil record. 1. Includes information about: a. structure of organisms
b. what they atec. what ate themd. what environment they lived ine. sequence of organisms from past
f. how organisms change over time
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17-1 The Fossil Record Fossils and Ancient Life
C. Fossil record provides incomplete information.
1. Over 99% of all species that have lived on Earth have become extinct.
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17-1 The Fossil Record How Fossils Form
II. How Fossils Form
A. Most fossils form in sedimentary rock.
1. Erosion causes existing rock to break into small particles of sand, silt, and
clay.
2. These particles fall to bottom of lakes, rivers, or the ocean.
3. Then sediments pile up in layers over time
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17-1 The Fossil Record How Fossils Form
Fossil FormationWater carries small rock particles to lakes and seas.
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17-1 The Fossil Record How Fossils Form
Dead organisms are buried by layers of sediment, which forms new rock.
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17-1 The Fossil Record How Fossils Form
The preserved remains may be later discovered and studied.
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17-1 The Fossil Record Interpreting Fossil Evidence
III. Dating Fossil Evidence
A. Paleontologists determine age of fossils using relative dating or radioactive dating.
B. Relative Dating1. Look at placement of fossils within the layers of rock
a. Oldest layers at bottom b. More recent layers on top
2. Can estimate a fossil’s age compared to other fossils & rock layers
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17-1 The Fossil Record Interpreting Fossil Evidence
Relative Dating
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17-1 The Fossil Record Interpreting Fossil Evidence
C. Radioactive Dating
1. Used to assign an absolute age to rocks.
2. Some elements are radioactive and steadily break down into nonradioactive elements. They are said to decay.
3. Uses the half-lives of radioactive elements to determine the age of a rock or fossil
a. Half-life is the length of time required for half of the radioactive atoms in a
sample to decay.
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17-1 The Fossil Record Interpreting Fossil Evidence
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17-1 The Fossil Record Interpreting Fossil Evidence
4. Scientists calculate the age of a sample based on the amount of
remaining radioactive isotopes it contains compared to non- radioactive elements.
a. They have tables of ratios that they can compare their data to get a more absolute age for the fossil.
●Compare amount of C-14 to C-12
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17-1 The Fossil Record Interpreting Fossil Evidence
5. Examples of radioisotopes: a. Carbon-14 ●Changes into N-14 as it decays
●Half-life is 5,730 years ●Useful for dating fossils less than 50,000 years old
b. Potassium-40 ●Changes into Ar-40 & Ca-40
●Half-life is 1.3 billion yearsc. Uranium-238 ●Half-life is 4.5 billion years
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17-1 The Fossil Record Geologic Time Scale
IV. Geologic Time Scale
A. First developed by studying rock layers and fossils worldwide. Later assigned dates with radioactive dating.
B. Geologic time is divided into Eras. 1. Oldest to youngest: Precambrian,
Paleozoic, Mesozoic, Cenozoic
C. Eras are divided into Periods. 1. Mesozoic Era divided into:
Triassic, Jurassic, Cretaceous
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17-1 The Fossil Record Geologic Time Scale
D. Geologic time begins with Precambrian Time, which covers about 88% of Earth’s history.
Vendian 650–544
DON’T COPY THE TABLES!DON’T COPY THE TABLES!
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17-1 The Fossil Record Geologic Time Scale
E. The Paleozoic began about 544 million years ago.
1. Many vertebrates and invertebrates lived during this time.
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17-1 The Fossil Record Geologic Time Scale
Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
290–245
360–290
410–360
440–410
505–440
544–505
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17-1 The Fossil Record Geologic Time Scale
F. The Mesozoic began about 245 million years ago.
1. Dinosaurs lived during this time.
2. Mammals began to evolve during this era.
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17-1 The Fossil Record Geologic Time Scale
Cretaceous
Jurassic
Triassic
145–65
208–145
245–208
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17-1 The Fossil Record Geologic Time Scale
G. The Cenozoic began about 65 million years ago and continues to the present.
1. Mammals became common during the Cenozoic.
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17-1 The Fossil Record Geologic Time Scale
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17-1 The Fossil Record
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Geologic Time Scale
Clock Model of Earth’s History
First humans
Firstprokaryotes
Cenozoic Era
Mesozoic Era
Paleozoic Era
Precambrian Time
First land plants
First multicellular organisms
Firsteukaryotes
Radiation of mammals
Accumulation of atmospheric oxygen
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17-1
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17-1
Which of the following statements about fossils is NOT true?
a. Most fossils form in sedimentary rock.
b. Fossils occur in a particular order.
c. Only a small portion of fossils are from extinct organisms.
d. Fossils can be used in relative dating of rock formations.
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The fossil record consistently shows evidence that
a. all forms of life have existed in all geologic eras.
b. living organisms have only been on Earth for a short time.
c. living things have changed over time.
d. ancient life-forms are much the same as forms found living today.
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Index fossils assist paleontologists in dating rocks because they represent species that
a. were widely distributed and existed for a very long time.
b. existed in a single location for a short period of time.
c. were widely distributed and existed for a short time.
d. existed in a single location for a very long time.
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Determining the age of a fossil by comparing its placement with fossils in other layers of rock is called
a. carbon-14 dating.
b. fossil-indexing.
c. relative dating.
d. absolute dating.
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17-1
According to the geologic time scale, geologic time begins with
a. Precambrian Time.
b. the Paleozoic Era.
c. the Quaternary Period.
d. the Cambrian Era.
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