Folding, tilting, faults, intrusions, and unconformities
all disturb rock layers. Sometimes, a single rock body may have been disturbed many times. Geologists must use their knowledge of the things that disturb rock layers to piece together the Earth’s history.
What are the ways the order of rock layers can be distributed?
The principle of superposition states that the oldest sedimentary rock units
are at the bottom, and the youngest are at the top
. Based on this, layer C is oldest, followed by B and A. So the full sequence of events is as follows: Layer C formed.
What causes the disturbance of rock layers?
But over millions of years,
the movement of tectonic plates
can disturb rock layers. A whole set of layers can get turned on its side. Rock layers can get bent, or even folded over, like taco shells that begin as flat tortillas. If a set of rock layers has been disturbed, the youngest layer may no longer be on top.
What are 2 ways that a rock layer can cause a gap in the geologic record?
At
a fault
, rock layers may move so they no longer line up. A fault is a break in rock where rocks can move. New rock layers can be worn away by erosion before they are covered by sediment. This makes a time gap in the rock layers.
What can happen when rock layers have been disturbed by faults or intrusions?
When rock layers have been disturbed by faults (a break or crack in Earth’s crust) or intrusions (a mass of igneous rock that forms when magma is injected into rock and then cools and solidifies),
determining relative age may be difficult
. In such cases, scientists may apply the Law of Crosscutting Relationships.
Which layers of rock are the oldest?
The law of superposition states that
rock strata (layers) farthest from the ground surface are
the oldest (formed first) and rock strata (layers) closest to the ground surface are the youngest (formed most recently).
What can scientists learn from the sequence of rock layers?
Fossils
found in a particular rock layer help scientists determine the age of the rock. Scientists use a technique called radiocarbon dating to find out the age of the fossils. Once they know the age of the fossil in the rock, they also know that rock itself is about the same age!
What are the 4 ways rock layers can be disturbed?
Folding, tilting, faults, intrusions, and unconformities
all disturb rock layers. Sometimes, a single rock body may have been disturbed many times. Geologists must use their knowledge of the things that disturb rock layers to piece together the Earth’s history.
What type of rock layer is easy to date?
It’s often much easier to date
volcanic rocks
than the fossils themselves or the sedimentary rocks they are found in. So, often layers of volcanic rocks above and below the layers containing fossils can be dated to provide a date range for the fossil containing rocks.
Why do you think some rock layers are missing from the sequence in some outcrops?
193 Page 4 DISCUSSION QUESTIONS: (Answer in Conpleie Sentences) 1. Explain why some rock layers can be missing from the sequence in some outcrops.
They were weathered and eroded or never deposited
. reconstruct a sequence of events?
What are 3 things that can change the position in which rock layers appear?
What can change the way rocks appear?
Gaps in the geologic record and folding
can change the position in which rock layers appear. Motion along faults can also change how rock layers line up.
Which layer is most likely the oldest?
The __________ layer is most likely the oldest. The answer is
bottom
. The law of superposition states that rock layers are deposited in such a way that the oldest rocks are at the bottom, whereas the younger rocks are on top. This law is used to identify the ages of rock layers.
What is a gap in the geologic record called?
Following on the Law of Original Horizontality and Law of Superposition, both Hutton and Lyell recognized erosional boundaries preserved between rock layers that represent gaps in the geologic record. They named these gaps unconformities.
What type of rock is produced if there is too much heat and pressure?
Metamorphic rocks
form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors.
Where are the oldest layers of rock found?
The oldest layers are
on the bottom
, and the youngest layers are on the top. Because sediments sometimes include once-living organisms, sedimentary rock often contains a lot of fossils. Fossils are once-living organisms that have been turned into rock, in which the shape or form of the organism can still be seen.
What are the layers of rock called?
Rock layers are also called
strata (the plural form of the Latin word stratum)
, and stratigraphy is the science of strata. Stratigraphy deals with all the characteristics of layered rocks; it includes the study of how these rocks relate to time.
