Name:__________________________________________________ Date:________________________
Chapter 10: A Trip Through Geologic Time
Section 1- Fossils
Objectives: After completing section 1 you should be able to: Explain how fossils formed; identify the different
kinds and types of fossils; describe what fossils can tell us about organisms and the environment of the past.
 What are fossils?
________________________________________________________________________________________
________________________________________________________________________________________
 Fossils provide evidence of _________________________________________________________________.
How Fossils Form
 Most fossils form when _____________________________________________________________.
 These sediments slowly ________________________________________________ the shapes of organisms.
 What is sedimentary rock?_________________________________________________________________
 What is the process of how a fossil forms?______________________________________________________
________________________________________________________________________________________
 Types of fossils found in rock include:
 ______________________________________
 ______________________________________
 ______________________________________
 ______________________________________
 How can other fossils form?
________________________________________________________________________________________
________________________________________________________________________________________
Molds and Casts
 Most common fossils
 What is a mold fossil and how does it form?
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
 What is a cast fossil and how does it form?
________________________________________________________________________________________
________________________________________________________________________________________
Petrified Fossils
 What does the word petrified mean? __________________________________________
 What is a petrified fossil and how does it form?
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
Carbon Films
 What is a Carbon film and how do they form?
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
 All living things contain carbon(a building block of life)
 Carbon films best preserve _______________________________________________________________
Trace Fossils
 What is a Trace Fossil and how is it formed?
________________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
Preserved Remains
 ________________________________________________ keep an organism preserved with little or no
change.
 Keeps organisms from ______________________________________.
Change Over Time
 Scientists who study fossils and classify them are called___________________________________________
 What do these scientists do?
________________________________________________________________________________________
________________________________________________________________________________________
 What does the fossil record provide?
________________________________________________________________________________________
________________________________________________________________________________________
Fossils and Past Environments
 Evidence of past climates
Give an example of how there is evidence from past climates__________________________________________
___________________________________________________________________________________________
 Changes in past environments and surface.
Give an example of how there are changes in past environments and surface of the Earth__________________
__________________________________________________________________________________________
Change in the Fossil Record
 Fossils occur in a _______________________________.
 Simple organisms came before __________________________________________
 Ex- one celled bacteria  modern humans
 Fossil record supports the ____________________________________.
 What is scientific theory?
________________________________________________________________________________________
________________________________________________________________________________________
 Evolution is______________________________________________________________________________
 Some organisms that were not able to evolve or adapt to their environment become ________________.
 Extinct- _________________________________________________________________________________
Section 2- The Relative Age of Rocks
Objectives: After completing section 2 you should be able to: State the law of superposition; describe how
geologists determine the relative age of rocks; explain how index fossils are useful to geologists.
What Does the Relative Age of Rocks Mean?
How do sedimentary rocks form?
___________________________________________________________________________________
 Fossils can be trapped in ____________________________.
How do we tell how old a rock and a fossil are?
 ______________________________________________- comparing the age of a rock to the rocks around it.
What is absolute age?
 ___________________________________________________________________________________
Compare the difference between relative and absolute age. ______________________________________________
_______________________________________________________________________________________________
So how do geologists determine the relative age of rocks?
 _____________________________________________________________________
 _____________________________________________________________________
 _____________________________________________________________________
The Law of Superposition
 Determines the _________________________________________
 In horizontal sedimentary rocks, the_________________________ layer is
____________________________ and the __________________________________________________
Clues from Igneous Rocks
How does an igneous rock form?
 __________________________________________________________
 Extrusion- __________________________________________________________
 Intrusion-__________________________________________________________
 Both types are always ___________________________________ than the rocks
____________________________________________________.
Clues from Faults
 What is a fault?______________________________________________________
 A fault is _______________________________________ than the rock that cuts through it.
 Why do movements along faults make it difficult to determine the relative age of rocks?_________________
________________________________________________________________________________________
Gaps in the Geological Record
 What is an unconformity?___________________________________________________________________
________________________________________________________________________________________
Explain how an unconformity can occur? _____________________________________________________________
________________________________________________________________________________________
Using Fossils to Date Rocks
 Certain fossils can help geologists match rock layers.
What is an index fossil?
________________________________________________________________________________________
________________________________________________________________________________________
Index fossils are useful because _____________________________________________________________________
Evolution of the Index Fossil- Ammonites
 Ammonites were_________________________________________that lived in shallow seas 500 million
years ago (mya) to their extinction 65 mya.
 Make a great index fossil for 2 reasons:
 _________________________________________________________________________________
 _________________________________________________________________________________
 Geologists ID them based on ___________________________________________of shells and based on
those differences can ID rock layers which certain ammonite fossils are found.
Section 3- Radioactive Dating
Objectives: After completing section 3 you should be able to: explain what happens during radioactive decay; and
describe what can be learned from radioactive dating.
Radioactive Decay
 What is an atom?______________________________________________________________________.
 Atoms of the same type of matter make up an __________________________
 H-Hydrogen, C-Carbon, N-Nitrogen, O-Oxygen (building blocks of life)
 As elements _________________________________________________ they
________________________________________ in a process called radioactive decay.
 During radioactive decay, atoms from ________________________________ break down to form atoms of
______________________________________.
 Radioactive- releases particles of energy.
 What determines the birthday of a rock?_______________________________________________________
 The radioactive elements in the rock will ______________________________________________________.
 How ________________________________ the radioactive elements ___________________
is_________________________________________________ (never changing)
 ____________________________________________ is called half-life.
 Half-life of a radioactive element is the _______________________________________________________
________________________________________________________________.
Absolute Dating
 _____________________________________- ancient remains of coral reefs; world’s oldest fossils.
 Geologists use _________________________________ to determine the
_______________________________________ of rocks.
 What is absolute age? ______________________________________________________________________
The Dating Game
 ______________________________________________-dating rocks using potassium-40
 This decays to argon-40 with a half-life of _____________________________________________.
 Very useful in dating rocks because it ________________________________________________.
Carbon-14 Dating
 Radioactive form of carbon is ___________________________________
 Remember carbon is a building block of life, all plants and animals contain
_____________________
 When an organism dies, carbon decays and turns into _____________________________.
 Scientists measure the amount _______________________ left in an organism to determine
__________________________________________.
 Very useful for dating organisms up to ______________________________ but not good
for__________________________
 The half-life of carbon-14 is _______________________________ years.
Radioactive Dating of Rock Layers
 Radioactive dating is good for ___________________________________ rocks but not
_____________________________________________ rocks.
 Where does the sediment from sedimentary rocks come from?_____________________________________
________________________________________________________________________________________
 Scientists can date __________________________ but not _______________________ from sedimentary
rocks.
 Scientists can also date igneous __________________&___________________ near sedimentary rock
layers.
 Why?___________________________________________________________________________________
The Geological Time Scale Section 4
Objectives: After completing section 4 you should be able to: Explain why the geologic time scale is used to show
Earth’s history; describe the different units of geologic time scale.
 Because the time span of Earth’s past is so great, geologists use the
_____________________________________________ to show Earth’s history.
 The geological time scale (GTS) is a
_______________________________________________________________
_______________________________________________________________________________________.
 Scientists study _______________________________ and _______________________________ worldwide
to create the GTS in ____________________________________________.
 Later, radioactive dating determined _______________________________________ of divisions in the GTS.
Divisions of Geological Time
 Changes in the fossil record mark where one time period _______________ and another ______________.
 Time on the scale starts at the beginning with _________________________________.
 After Precambrian Time, basic units of the GTS are __________________________________.
 Eras- ____________________________________________________________________________.
 Ex: The ______________________, _______________________, and __________________ Eras
 Periods-_____________________________________________________________________.
 Ex: The Mesozoic Era includes 3 periods: The Triassic, Jurassic, and Cretaceous Periods.