Chapter 7 Notes (Part 1)
Name:___________________________________
A Trip Through Geologic Time
Date:____________________ Period:_______
Plate Tectonics and Pangea
The land masses of Earth are in constant
______________.
Plate ________________ refers to the
fact that earth’s crust is made up of
several ________________ called plates
that are constantly moving.
About 225 million years ago, all of the
dry land mass existed as __________
large supercontinent known as
________________________.
Over _________________ of years the
tectonic plates that make up earth’s crust
have drifted apart leading to the _____
continents we know today.
Fossils
Most fossils form when living things ________ and are buried by _____________________. The sediment
slowly hardens into ___________ and preserves the shapes of the organisms. Most fossils are found in
_________________________________ rock because most fossils form from animals or plants that once lived
in or near quiet ____________________ such as swamps, lakes, or shallow _____________ where
__________________________ builds up.
Types of Fossils
Petrified Fossils – are fossils in which _________________________ replace part or all of an organism.
Molds – a ________________ area in sediment in the shape of an organism or part of an organism.
Casts – a solid copy (replica) of an organism which results when water may deposit __________________ into
a mold.
Carbon Films – an extremely ___________ coating of ______________________ on rock. When sediment
buries an organism, some gases escape leaving carbon behind. This process can preserve the delicate parts of
________________ and ________________________.
Trace Fossils – provide evidence of the __________________________ of ancient organisms. Examples are
things such as a fossilized footprint, trail, or ________________________.
Preserved Remains – result when an ___________________ organism is preserved. Examples are frozen
fossils (like the baby wooly mammoth) and amber preserved fossils (like the “classic” Jurassic Park mosquito).
Chapter 7 Notes (Part 2)
Name:___________________________________
A Trip Through Geologic Time
Date:____________________ Period:_______
How Old Are Rock Layers?
RELATIVE DATING
The Law of ___________________________ states that in _________________________ horizontal layers of
sedimentary rock, the __________________ layer is on the bottom and each higher layer is ________________
than the layers below it.
It should also be noted that “cross-cuts” seen in layers of sedimentary rock such as intrusions and extrusions are
___________________ than the layers that they cut through.
Examine the diagram below and list the rock layers in order from OLDEST to YOUNGEST.
_______
_______
_______
_______
________
________
Index fossils are useful because they tell the relative ages of the rock layers in which they occur. To be useful
as an index fossil, a fossil must be _____________ distributed and represent an organism that existed for a
geologically ______________ period of time.
Examine the diagram. Which layer contains a good index fossil? _______ Why?
There are __________ in the geologic
record due to __________________ of
sedimentary rock layers and loss of
exposed rock layers due to
_________________. This gap in the
geologic record is called
_______________________.
--------------------------------------------------------------------------------------------------------------------------------------RADIOMETRIC DATING
It has been discovered that although most elements do not change, some elements can break down, or _______,
over time. These elements release particles and ____________ in a process called _______________________
decay. During the process of radioactive decay, the atoms of one element break down to form _____________
of another element. The _________ of decay for particular elements never changes. The _________________
of a radioactive element is the time it takes for __________ of the radioactive atoms to decay.
EXAMPLE: The half-life of Carbon-14 is 5,730 years which means
that if you start with a 100 gram sample of Carbon-14, in
approximately 5,730 years there will only be 50 grams of Carbon14 left in the sample because half of it would have decayed.
Complete the Chart
Number of Half-lives
1
2
3
4
% of Original Element Remaining
______
______
______
______
Sample Problem: A rock from the moon contains
12.5% of the potassium-40 it began with. How old is
the rock?
Step 1: Figure out how many half-lives have passed for
that element. _________
Step 2: Multiply the number of half-lives from Step 1
by the time each half-life is worth using the information
given in the table.
Solution: ________ X ________ = _______________