2/9/2020
USATestprep, LLC
Relative Dating
Student Name:
_______________________
Teacher Name: Kyanna Jenkins
_________
Score: _________
Date:
Listed in the Item Bank are some important labels for sections of the image below. Write the number for each label in the corresponding area it identifies in
the image.
The earth is estimated to be about 4.5 billion years old. Rocks and rock formations found throughout earth’s crust give scientists clues to the past. They
assume that the processes that acted on the crust millions of years ago are the same processes that act on and within earth today. This is called the
principle of uniformity or uniformitarianism.
The law of superposition helps us infer the age of rock layers, or strata. This law states that, if layers of rock are left undisturbed, the layers at the bottom
are the oldest. The lower layers must be in place before younger layers can be deposited on top of them. Scientists infer the relative age of the layers as
well as any fossils found within them.
The law of superposition does have exceptions. Some processes within the earth cause younger layers to be moved below older. Folding, faulting, and
intrusion can cause these exceptions. Regardless of position, any rock is always older than the process that changed it.
An igneous intrusion is molten rock, referred to as magma when underground, that is injected into older pre-existing rock layers. It eventually cools and
crystalizes to form igneous rock. Intrusions are younger than all the rock layers that are in contact with them. An igneous extrusion is formed from molten
rock (called, in this case, lava) that reaches the surface of Earth. An extrusion must be younger than the layers below it, but older than any future layers
that might be deposited above.Rocks are deposited in horizontal layers called strata. Folds are bends in rock layers, caused by intense pressure within the
earth. Sometimes folding can overturn strata so older layers lie on top of younger. A fault is a break in earth’s crust along which there is movement.
Items:
1
Deposition
2
Erosion
3
Faulting
4
Igneous intrusion
5
Oldest layer
6
Youngest layer
https://www.usatestprep.com/modules/dragdrop/gallery.php?testid=568&strandid=2980
1/2
2/9/2020
USATestprep, LLC
https://www.usatestprep.com/modules/dragdrop/gallery.php?testid=568&strandid=2980
2/2