23.6 Earth's History Flashcards
What is the relative age of rock?
its age compared to the ages of other rocks above or below it in a sequence of rock layers.
How do geologists determine the relative age and absolute age of rock layers?
Law of Superposition to determine relative ages of sedimentary rocks from the sequence of rock layers and the fossils within each layer
Geologists use radioactive dating to determine the absolute ages of rocks
What is absolute age?
time that has passed since the rock has formed
What is the Law of Superposition?
states that if rock layers are undisturbed, younger rocks lie above older rocks, and the oldest rocks are at the bottom
What is an extinct species?
type of organism that is no longer living
What are index fossils?
fossils of organisms that are easily identified, occurred over a large area, and lived during a well-defined period of time.
These are used to determine the relative age of rocks along with the Law of Superposition
What forms the basis of the geologic time scale?
The geologic time scale is based on the relative ages of rock layers and the use of radioactive dating to find the absolute ages of rock
What are the major divisions of Earth’s history?
Eras>Periods. the major divisions of Earth’s history are Precambrian Time (4.6 Billion - 544 Million Years Ago), Paleozoic (544 - 248 Million Years Ago), Mesozoic (248-65 Million Years Ago), and the Cenozoic (65 Million Years Ago - Present)
What is an era?
large units of Earth’s history in time
What is a period?
Division of era that is a unit of Earth’s history in time
What is a mass extinction? How many have occurred?
Boundaries between eras that mark a time when many different organisms became extinct within a relative short amount of time.
Thus far, there have been 5 mass extinctions on Earth
