Download UNIT 2, CHAPTER 5:

UNIT 2, CHAPTER 5:
Fossils and Geologic Time
Topic 1:
The Geologic Column
Pages 156-161
As rocks are weathered, eroded, and deposited their sediments form layers that eventually
become compacted and cemented into solid rock called sedimentary rock. These rocks
play an important role in helping geologists and paleontologists (scientists who study
ancient life forms) to reconstruct the history of Earth and life on it.
1. The location of rock layers and the fossils they contain relative to one another
allows scientists to determine whether an object or event is older or younger than
another object or event. This process is called ___________________
__________________ and uses the principle of _________________________,
which states that in an undisturbed sequence of sedimentary layers,
__________________ rocks lie above _______________ rocks.
2. To reconstruct the complete history of Earth, layers of rock from around the world
must be compiled into one single sequence (from oldest on the bottom to
youngest on the top) called the ________________________
______________________. This is like collecting pages from a book that have
been torn out and putting them together in the correct order to reconstruct the
story.
3. There is no one location on Earth that has rock layers formed during all periods of
earth’s history. These breaks in the geologic record in a sequence of rock layers is
called a(n) ________________________________.
4. Breaks in the rock record (missing layers) can result from
_______________________, meaning that the supply of sediment is cut-off. This
usually occurs when uplift raises the land above sea level for a period of time
(since sedimentary rocks form offshore, underwater). They also can be formed
and later removed when the land is raised by the process of
__________________.
Topic 2:
Radiometric Dating
Pages 162-165
1. ____________________ __________________ is any process used to determine
the age of an object or event in years. The most common method used by
scientists to accomplish this uses the natural process of __________________
________________ in which radioactive isotopes of certain elements within
rocks break down into stable isotopes of other elements at a steady, predictable
rate. This method was invented on 1907 shortly after the discovery of
radioactivity is 1896. Prior to this time, geologists were divided and debated the
age of the earth.
2. Unstable radioactive isotopes used to date rock are called the
_________________ and the stable material produced by its decay is called the
_______________________. By comparing the relative amount of these
materials, the age of the rock can be determined. The more
____________________ material there is, the older the rock.
3. Using radioactive decay to determine the age of a rock or fossil is called
_______________________ _____________________. This can be
accomplished by knowing how much of the parent material has decayed, and the
rate at which it decays, known as its ______________ _______________. This
rate is used since the parent material never completely decays.
4. There are many different radioisotopes used to determine the ages of rock or
fossils of different ages. The __________________ method is commonly used to
determine when animal fossils died and works well for dating things that lived
within the last 50,000 years.
TOPIC 3:
Fossils
Pages 166-171
1. The remains or physical evidence of an organism preserved by geologic processes
is called a ______________________. These are most often preserved in
_________________________ rock but may also be found preserved in
_________________________ , ________________________, or
______________.
2. _____________________________ is a process in which minerals replace an
organism’s tissues. A good example of this is _________________________
wood.
3. _________________________ is hardened tree sap and can preserve all parts
(hard and soft) of small insects. ____________________ forms thick, sticky pools
that have trapped and preserved organisms that have lived in more recent times.
____________________ contains almost no decomposing bacteria and can
preserve organisms almost perfectly for tens of thousands of years.
4. The fossil record reveals a history of ________________________ change.
___________________ fossils help reconstruct ancient coastlines and the uplift of
mountains. Fossils of plants and animals can help in the reconstructing of past
______________________.
Continued on page 2…
5. By studying the relationships between fossils found in different parts of the
geologic column, scientists can interpret how ________________ has changed
over time. Finally, using fossils of organisms that only existed for a short span of
identified time, they can determine the absolute age of rock that they are found in
without relying on radiometric dating methods. These types of fossils are known
as ______________________ ______________________ and include such
fossils as _______________________________ and
____________________________.