Unit at a Glance
Chapter 6: The Rock and Fossil Record
Standards
S6E5: Students will investigate the scientific view of how the Earth's surface is
formed.
b. Investigate the composition of rocks in terms of minerals.
c. Describe the processes that change rocks and the surface of the Earth.
f. Describe how fossils show evidence of the changing surface of the Earth.
Unit Vocabulary
Uniformitarianism: the idea that the same geologic processes shaping the Earth today
(weathering, erosion, and deposition) have been at work throughout Earth’s history. In this idea
the Earth’s surface changes slowly.
Catastrophism: the idea that states that geologic change on the surface of the Earth happens
through catastrophic events and natural disasters. In this idea the Earth’s surface is changed
quickly.
Paleontology: the study of fossils.
Extinction: the death of every member in a species.
Fossil: the remains OR physical evidence of an organism that has been preserved by
geological processes.
Trace Fossil: fossilized marks or traces that are formed in soft sediment by the activities of
animals.
Mold: a mark or depression that is made in a sedimentary surface by a shell or other body that
is now decomposed.
Cast: a type of fossil that forms when sediments fill in the depression created (the mold) left by
a decomposing organism.
Index Fossil: a fossil that is found in rock strata of only one age that is used to establish the age
of the rock layers around it.
Relative Dating: any method of determining whether an event or object is older or younger
than other events or objects (estimating the age of something by using other objects whose
ages may be known).
Geologic Column: the ideal arrangement of rock layers on the Earth in which the oldest rocks
are at the bottom and the youngest rocks are at the top.
Principle of Superposition: the principle that states that younger rock strata lie above older rock
strata if the layers have not been disturbed.
Unconformity: a break in the geologic record (rock strata) created when layers of rock are
disturbed or sediment is not deposited.
Unit at a Glance
Absolute Dating: any method of measuring the exact age of an object or event in years.
Radiometric Dating: a method of determining the age of an object by estimating the relative
percentages of a radioactive isotope remaining in a sample compared to the percentages of
stable isotopes.
Isotope: an atom that has the same number of protons as other atoms of the same element,
but that has a different number of neutrons making the element radioactive.
Half-life: the time needed for HALF of a sample of a radioactive substance to undergo
radioactive decay.
Geologic Time Scale: the standard method used to divide the Earth’s 4.6 billion year history into
manageable parts.
Eon: the largest division of geologic time.
Era: a smaller unit of geological time that divides eons and that includes two or more periods.
Period: the unit of geologic time smaller than an era and into which era are divided.
Epoch: the smallest unit of geologic time and a division of the geologic period.
Essential Questions
What is the difference between
How can scientists use the fossils they find
Uniformitarianism (Gradualism) and
to learn about the Earth’s History?
Catastrophism?
What theory (Uniformitarianism or
How do scientists use relative dating to
Catastrophism) do MODERN geologists
determine the age of rock strata?
support?
How many different ways can fossils be
How do scientists use absolute dating to
made? Explain.
determine the age of rock strata?