Geologic Time Scale
Geologists estimate that the earth is about
4.6 billion years
The age of an object in relation to the ages of other objects is
Relative Age
If the percentage of daughter isotopes present in a radioactive sample is greater than the percentage of parent isotope,
the rock is older
Younger layers of undisturbed sedimentary rock are above older layers according to
law of superposition
The principle that Earth’s history can be explained by current geologic processes is
Uniformitarianism
What geologic unit of time is longer than an epoch but shorter than an era?
Period
What are the criteria for a fossil to be considered an index fossil?
Scattered over a large area,distinguished features, short span of time, large numbers
What are three ways other the radiometric dating to get the absolute age of an object?
tree rings, ice core, and varve
A fault or body of rock is younger than any other body of rock it cuts through according to the law of
cross- cutting relationships
What is the name of the Scottish scientist who came up with the idea of uniformitarianism?
James Hutton
The scale that outlines the development of Earth and the life on Earth is called the:
geologic time scale
Fragments of existing rocks incorporated into other layers of rock are called
Inclusive Rock
How is radioactive decay used to determine the absolute age of rocks?
Parent isotopes are compared to daughter isotopes.
Scientists can assume that sedimentary rock layers that are not horizontal have been tilted or deformed by crustal movements after the layers formed by using the
Principal of Original Horizontality
Organisms that formed index fossils lived during a _____ span of geologic time.
short
Lists the eons of geologic time in order from oldest to most recent
apoch/epoch
The matching of rock outcrops or fossils exposed in one geographic region to similar outcrops or fossils exposed in other geographic regions
Correlation
What isotope is used to date objects less than 60,000 years old.
Carbon-14
The numeric age of an object is called
Absolute age
If an igneous intrusion is observed through a layer of sedimentary rock, what geological law applies?
Cross-Cutting Relationships
Lists the eons of geologic time in order from oldest to most recent
Hadean, Archean, Proterozoic, Phanerozoic
Index fossils found in rock layers in different areas of the world indicate that the rock layers
formed during the same period of time
Why is radioactive decay used to determine the absolute age of rocks?
Radioactive decay does not happen at a constant rate.
The idea that states that if sedimentary rock is left undisturbed will remain in horizontal layers is called
original horizontality
How many half-lives would be necessary for a sample of parent isotopes to decay to the point that only one-fourth of the sample is composed of parent isotopes?
2