Unit 2C Review

Geologic Time

Question: Layers of rock are also called this

____  ____  ____ ____  ____  ____

Answer: strata

Question: How old is Earth?A
Answer: Approximately 4.6 billion years old.

Question: Why do scientists want to organize geologic time?
Answer: To understand changes that have occurred over time.  To predict what may occur in the future.  To communicate with others about Earth's history.

Question: Why are fossils important to the understanding of geologic time?
Answer: Fossils tell of creatures that lived long ago.  Fossils attempt to give scientists a clearer picture of events that took place in the past.

Question: What's the name of the geologic time period that is characterized by the Age of Dinosaurs?
Answer: The Jurassic Period.

Organizing Time

Question: Earth was formed and became hospitable for living organisms during this first geologic time period.
Answer: The Hadean period or the Precambrian period.

Question: Why are mass extinctions important in the development of Earth's geologic time scale?
Answer: Mass extinctions indicate when old time periods are over and new time periods begin.

Question: What allowed most mammals to increase in number during the Cenozoic era?
Answer: Increase in atmospheric oxygen levels.  Increase in the availability of water.

Question: What epoch are we currently in?
Answer: Holocene has existed for the last 11,000 years.

Question: Order the following geological time units from largest to smallest: epochs, periods, eons, eras.
Answer: Eons, eras, periods, epochs

Relative-Age Dating

Question: Why are geologic principles useful in determining Earth's history?
Answer: There are no written records of Earth from long ago.  Scientists can only rely on the geologic principles to piece together and understand the history of Earth.

Question: Why are geologic principles used to determine the history of Earth?
Answer: There is no written record of Earth events many millions of years ago.  The principles are used to piece together events scientists think have happened to better appreciate how the Earth has changed.

Question: Which scientists thought the Earth was really old?
Answer: James Hutton (1700s)

Question: Define uniformitarianism.
Answer: Principle that states "geologic processes that have occurred in the past also occur and behave the same way today."

Question: Give an example of uniformitarianism.
Answer: Volcanoes exploding, lava flowing, waves crashing onto shore, mountains weathering, rivers flowing, ice melting and freezing, etc.

Geologic Principles

Question: Can Earth's age be predicted?
Answer: Depends on who you ask...4.6 billion years ago is a pretty accurate age.  The problem is there is still so much to be studied about the geology of Earth that could give more clues.

Question: Which principle describes "an intrusion is younger than the rock it cuts across."
Answer: Cross-cutting relationships

Question: Describe the principle of superposition.
Answer: Principle that states in an undisturbed rock sequence, the oldest rocks are at the bottom and each consecutive layer is younger than the layer beneath it.

Question: Identify the principle that states that the fragments in a rock layer must be older than the rock layer that contains them.
Answer: Principle of inclusions.

Question: State the principle of original horizontality.
Answer: Sedimentary rocks are deposited or layed down in horizontal or near horizontal layers.


Question: Define fossil.
Answer: Preserved remains of once living organisms.

Question: Give an example of original preservation.
Answer: Mammoths frozen in ice, insects trapped in tree sap, petrified trees

Question: A fossil that forms when the hollowed out impression of a once living organism is left behind in sedimentary rock layers.
Answer: What is a mold?

Question: Give an example of a trace fossil.
Answer: worm trails, animal burrows, animal footprints

Question: Type of fossil that is easily recognized and can be found in many various places around the world.
Answer: Index fossil