Explore 3.16 What Earth’s Materials & Features Can Teach Us and How We Learn It
Learning Objectives
By the time you have completed the 3.16. Introduction & Exploration Activities, you should be able to:
Understand the meaning of the following terms/concepts and be able to identify examples of each: sequence of Earth events, age of Earth events, nature of Earth events, relative dating, the principles of relative dating, the principle of fossil succession, radiometric dating, structure of Earth materials, composition of Earth materials, source of Earth materials, processes that modify Earth materials, igneous rocks, sedimentary rocks, metamorphic rocks, erosional surfaces, faults and tilted sedimentary rocks.
Illustrate how important scientific interpretations about the sequence, age, and nature of past Earth events are derived from scientific observations of the structure and composition of rocks.
Identify a likely kind of Earth change or event, given an Earth material or feature—and vice versa. (For example, identify that an igneous rock indicates tectonic processes produced magma—and vice versa.)
Use the principles of relative dating to determine the sequence of events that produced the relationships illustrated in a geologic block diagram.
Understand relative dating and how to use its principles to sequence events. Also, understand absolute dating and how humanity determines the ages of Earth events.
Identify a likely way an Earth event (e.g., volcanic eruption) could be recorded for future observers such as modern humans (e.g., as a deposit of volcanic rock).
Scientific Terms/Concepts
Terms: Sequence of Earth Events, Absolute Dating, Nature of Earth Events, Relative Dating, Principles of Relative Dating, Principle of Fossil Succession, Radiometric Dating, Structure of Earth Materials, Composition of Earth Materials, Source of Earth Materials, Processes that Modify Earth Materials, Igneous Rocks, Sedimentary Rocks, Metamorphic Rocks, Erosional Surfaces, Faults, and Tilted Sedimentary Rocks
Define and give an example of each term:
Term:
Sequence of Earth Events
Definition:
Answer: Sequencing Earth events involves determining the order in which geologic events occurred. We may not have exact ages, but we can determine which event came before the other.
Sequencing Earth events involves determining the order in which geologic events occurred. We may not have exact ages, but we can determine which event came before the other.
Example:
Answer:An example of sequencing would be that my father is older than me. My grandfather is older than my father. Thus my grandfather is also older than me. A common example when using geology is to determine which layers of rock are older and which are younger by relative dating. For example, layer E in the above image is younger than layer C.
An example of sequencing would be that my father is older than me. My grandfather is older than my father. Thus my grandfather is also older than me.
A common example when using geology is to determine which layers of rock are older and which are younger by relative dating. For example, layer E in the above image is younger than layer C.
Term:
Absolute Dating
Definition:
Answer: Absolute Dating involves ascertaining the time that elapsed after the event occurred. Essentially it gives us an exact age (or close to the exact age) of an event.
Absolute Dating involves ascertaining the time that elapsed after the event occurred. Essentially it gives us an exact age (or close to the exact age) of an event.
Example:
Answer: If we know my dad was born in 1970 and I was born 20 years after him, we can ascertain that I was born in 1990 and can be dated based on that information.
If we know my dad was born in 1970 and I was born 20 years after him, we can ascertain that I was born in 1990 and can be dated based on that information.
Term:
Nature of Earth Events
Definition:
Answer: Identifying the nature of Earth events involves discovering the attributes of that event. Understanding the nature of the events that occur helps us to understand what happened in the past and why the earth looks the way it does.
Identifying the nature of Earth events involves discovering the attributes of that event. Understanding the nature of the events that occur helps us to understand what happened in the past and why the earth looks the way it does.
Example:
Answer: In this example we have lines labeled A and F. These fault lines are likely the result of an earthquake that caused the shift we see in the layers. Understanding the nature of the event helps us understand why the earth looks this way in the example.
In this example we have lines labeled A and F. These fault lines are likely the result of an earthquake that caused the shift we see in the layers. Understanding the nature of the event helps us understand why the earth looks this way in the example.
Term:
Relative Dating
Definition:
Answer: Relative dating uses simple, powerful principles to determine sequences of Earth events.
Relative dating uses simple, powerful principles to determine sequences of Earth events.
Example:
Answer: With relative dating, we can determine the sequence of events that caused Earth to look the way it currently does. We can see that rock layers are older or younger than the land surrounding it.
With relative dating, we can determine the sequence of events that caused Earth to look the way it currently does. We can see that rock layers are older or younger than the land surrounding it.
Term:
Principles of Relative Dating
Definition:
Answer:The principle of original horizontality states that sediments originally form in horizontal layers. Superposition indicates that, where undisturbed, older sedimentary layers lie beneath younger layers. Lateral continuity indicates that sedimentary layers separated by erosion were once continuous. The principle of crosscutting relationships indicate that broken rock bodies are older than the features that cut across them. The principle of inclusions indicate that materials inside rocks existed before the rock that contains them.
The principle of original horizontality states that sediments originally form in horizontal layers. Superposition indicates that, where undisturbed, older sedimentary layers lie beneath younger layers. Lateral continuity indicates that sedimentary layers separated by erosion were once continuous. The principle of crosscutting relationships indicate that broken rock bodies are older than the features that cut across them. The principle of inclusions indicate that materials inside rocks existed before the rock that contains them.
Example:
Answer: In the image above, original horizontality tells us that the layers B-H were originally formed horizontally, so something must have caused them to tilt. Superposition tells us layer F is older than layer E. Lateral continuity tells us that layer E was cut by erosion (J) and that layer E on both sides of the divide are the same. Crosscutting tells us that intrusion G is younger than layers H and F, which it cuts through. Inclusions tell us that rock I existed before layer F and is thus older than layer F. The squiggly line marked D indicates erosion has occurred.
In the image above, original horizontality tells us that the layers B-H were originally formed horizontally, so something must have caused them to tilt.
Superposition tells us layer F is older than layer E.
Lateral continuity tells us that layer E was cut by erosion (J) and that layer E on both sides of the divide are the same.
Crosscutting tells us that intrusion G is younger than layers H and F, which it cuts through.
Inclusions tell us that rock I existed before layer F and is thus older than layer F.
The squiggly line marked D indicates erosion has occurred.
Term:
Principle of Fossil Succession
Definition:
Answer: The principle of fossil succession indicates that the fossil patterns in successions of sedimentary layers are predictable across broad areas—sometimes across Earth.
The principle of fossil succession indicates that the fossil patterns in successions of sedimentary layers are predictable across broad areas—sometimes across Earth.
Example:
Answer: Groups of the same fossil will appear in the same order vertically through the earth. Together with principles of relative dating, we can determine how old different layers of earth are. For example, we may find one kind of fossil in layer H. Then we may find a different kind in layer E. The fossil in layer E should exist on both sides of the erosion area marked J.
Groups of the same fossil will appear in the same order vertically through the earth. Together with principles of relative dating, we can determine how old different layers of earth are.
For example, we may find one kind of fossil in layer H. Then we may find a different kind in layer E. The fossil in layer E should exist on both sides of the erosion area marked J.
Term:
Radiometric Dating
Definition:
Answer: Radiometric dating typically measures material formation by observing the proportion of radioactive parent and stable daughter isotopes. Decay rates of different isotopes vary from much less than a second to many billions of years. The constancy of individual decay rates makes radiometric dating the most accurate, reliable and widely applicable dating method. In other words, radioactive material allows us to determine a more specific age of material.
Radiometric dating typically measures material formation by observing the proportion of radioactive parent and stable daughter isotopes. Decay rates of different isotopes vary from much less than a second to many billions of years. The constancy of individual decay rates makes radiometric dating the most accurate, reliable and widely applicable dating method.
In other words, radioactive material allows us to determine a more specific age of material.
Example:
Answer: A common method of radioactive dating is carbon dating. Carbon has a half-life of 5,730 years (meaning it takes 5,730 years for half a sample of carbon 14 to decay to nitrogen 14). When dating the earth, it is more common to use uranium-lead dating (U-Pb). U-Pb has a half life of 4.5 billion years. Since the earth is very old, it is helpful to use something very old to date it.
A common method of radioactive dating is carbon dating. Carbon has a half-life of 5,730 years (meaning it takes 5,730 years for half a sample of carbon 14 to decay to nitrogen 14).
When dating the earth, it is more common to use uranium-lead dating (U-Pb). U-Pb has a half life of 4.5 billion years. Since the earth is very old, it is helpful to use something very old to date it.
Term:
Structure of Earth Materials
Definition:
Answer: The structure of Earth materials include the geometric relationships between rock bodies and between the components of a rock body.
The structure of Earth materials include the geometric relationships between rock bodies and between the components of a rock body.
Example:
Answer: The earth is divided into layers. The crust and mantle are rigid, with a plastic layer between them. The core is also rigid, with a liquid outer core.
The earth is divided into layers. The crust and mantle are rigid, with a plastic layer between them. The core is also rigid, with a liquid outer core.
Term:
Composition of Earth Materials
Definition:
Answer: The composition of Earth Materials includes the types of materials that comprise the rock and their elemental and isotopic makeup.
The composition of Earth Materials includes the types of materials
that comprise the rock and their elemental and isotopic makeup.
Example:
Answer: The different layers of the earth are composed of different materials. For example, the core is mostly iron and nickel. But the crust is where you would find the rocks and minerals we see today, like granite and basalt.
The different layers of the earth are composed of different materials. For example, the core is mostly iron and nickel. But the crust is where you would find the rocks and minerals we see today, like granite and basalt.
Term:
Source of Earth Materials
Definition:
Answer: The source of Earth materials describes where the materials on earth came from.
The source of Earth materials describes where the materials on earth came from.
Example:
Answer: Weathered granite is the source of most beach sand. Magma is the source of granite.
Weathered granite is the source of most beach sand. Magma is the source of granite.
Term:
Processes that Modify Earth Materials
Definition:
Answer: The processes that form or modify materials are the natural events that cause the materials to change.
The processes that form or modify materials are the natural events that cause the materials to change.
Example:
Answer: Burial is the process that converts plant material into coal. Partial melting is the process that produces magma from solid upwelling rock in Earth’s mantle.
Burial is the process that converts plant material into coal. Partial melting is the process that produces magma from solid upwelling rock in Earth’s mantle.
Term:
Igneous Rocks
Definition:
Answer: Igneous Rocks form when hot magma cools enough to solidify into a rock. These rocks indicate that tectonic processes produced magma that moved into or through the crust. All rocks are linked through the rock cycle. As magma solidifies, it creates igneous rock. Any time a rock heats enough to melt, it will become an igneous rock again as it solidifies.
Igneous Rocks form when hot magma cools enough to solidify into a rock. These rocks indicate that tectonic processes produced magma that moved into or through the crust.
All rocks are linked through the rock cycle. As magma solidifies, it creates igneous rock. Any time a rock heats enough to melt, it will become an igneous rock again as it solidifies.
Example:
Answer: Granite, basalt, pumice, and obsidian are common examples of igneous rocks.
Granite, basalt, pumice, and obsidian are common examples of igneous rocks.
Term:
Sedimentary Rocks
Definition:
Answer: When sediment settles or deposits and then is subject to time, it compresses into a rock. That is called sedimentary rock. Sedimentary rocks indicate the nature of Earth’s surface at the time they formed. All rocks are linked through the rock cycle. Any time a rock is exposed to wind or water, it can erode and create sediment that can then solidify and turn into a sedimentary rock.
When sediment settles or deposits and then is subject to time, it compresses into a rock. That is called sedimentary rock. Sedimentary rocks indicate the nature of Earth’s surface at the time they formed.
All rocks are linked through the rock cycle. Any time a rock is exposed to wind or water, it can erode and create sediment that can then solidify and turn into a sedimentary rock.
Example:
Answer:Conglomerate, mudstone, sandstone, and limestone are common examples of sedimentary rocks.
Conglomerate, mudstone, sandstone, and limestone are common examples of sedimentary rocks.
Term:
Metamorphic Rocks
Definition:
Answer: Metamorphic rocks form when a rock undergoes immense heat and/or pressure that changes the composition of that rock. Metamorphic rocks indicate how mountain belts and continental crust form and develop. All rocks are linked through the rock cycle. Any time a rock is exposed to great amounts of heat and pressure, it will change and become a metamorphic rock.
Metamorphic rocks form when a rock undergoes immense heat and/or pressure that changes the composition of that rock. Metamorphic rocks indicate how mountain belts and continental crust form and develop.
All rocks are linked through the rock cycle. Any time a rock is exposed to great amounts of heat and pressure, it will change and become a metamorphic rock.
Example:
Answer: Gneiss, schist, marble, and slate are common examples of metamorphic rocks.
Gneiss, schist, marble, and slate are common examples of metamorphic rocks.
Term:
Erosional Surfaces
Definition:
Answer: Erosion is what happens when wind or water slowly wear away rock. An erosional surface is a rock that was formed by erosion. Erosional surfaces record the removal (destruction) of previously formed rock from Earth’s surface.
Erosion is what happens when wind or water slowly wear away rock. An erosional surface is a rock that was formed by erosion. Erosional surfaces record the removal (destruction) of previously formed rock from Earth’s surface.
Example:
Answer: Note the erosional surface between the tilted red sedimentary rocks that lie below the tan layer of gravel.
Note the erosional surface between the tilted red sedimentary rocks that lie below the tan layer of gravel.
Term:
Faults
Definition:
Answer: Motion near plate boundaries can deform the rocks that comprise these plates. Deforming the lower rocks causes them to flow but causes the upper rocks to break. These fractures (across which rock bodies move) are called faults.
Motion near plate boundaries can deform the rocks that comprise these plates. Deforming the lower rocks causes them to flow but causes the upper rocks to break. These fractures (across which rock bodies move) are called faults.
Example:
Answer:
Term:
Tilted Sedimentary Rocks
Definition:
Answer: Sedimentary rocks are comprised of horizontal layers. Thus, the tilt of these sedimentary rocks indicates that tectonic activity changed their original orientation. Faults and tilted sedimentary rocks indicate stresses that shifting tectonic plates caused brittle rocks in Earth’s crust to break, deform and move.
Sedimentary rocks are comprised of horizontal layers. Thus, the tilt of these sedimentary rocks indicates that tectonic activity changed their original orientation.
Faults and tilted sedimentary rocks indicate stresses that shifting tectonic plates caused brittle rocks in Earth’s crust to break, deform and move.
Example:
Answer:
Identifying Earth’s Age
Put the letters from the above image in order from oldest to youngest.
*Oldest
Answer:
G A metamorphic rock body
Description:
This layer is at the bottom of the cross-section. Superposition tells us it is the oldest layer, because it lies beneath the other layers.
Answer:
A A fault
Description:
This fault cuts through layer G only. Crosscutting relationships tell us that this fault is younger than the rock that it cut across.
Answer:
B An igneous intrusion
Description:
This igneous intrusion cuts through the metamorphic body (G) and the fault that cuts it (A), but it doesn’t cut through any other layers. In fact, you can see that it is broken by fault F, which must have happened after the intrusion. The intrusion would be younger than anything it cuts through, as taught by crosscutting relationships.
Answer:
C Sedimentary Rock Layers
Description:
This layer is yonder than everything below it, as we learn from the principle of superposition. But since it is cut by fault F, it must be older than the fault.
Answer:
D An igneous intrusion
Description:
This igneous intrusion cuts through all the layers except for layer E.The principle of crosscutting relationships tells us it is younger than everything it cuts through.
Answer:
E Sedimentary rock layers
Description:
Layer E is at the top of this image. Superposition tells us that where undisturbed, older sedimentary layers lie beneath younger layers. Thus, layers at the top should be younger. The only thing that disturbs layer E is the fault F.
*Youngest
Answer:
F A fault
Description:
This fault cuts through the entire cross section. You can even see some uplift on layer E at the far left part of the image. This fault represents the youngest event here.
The principle of original horizontality states that sediments originally form in horizontal layers. Superposition indicates that, where undisturbed, older sedimentary layers lie beneath younger layers. Lateral continuity indicates that sedimentary layers separated by erosion were once continuous. The principle of crosscutting relationships indicates that broken rock bodies are older than the features that cut across them. The principle of inclusions indicate that materials inside rocks existed before the rock that contains them.
What is a likely event that could cause the fault line listed as F in the above image?
Answer: Earthquakes are the most common cause of a fault line. Any time two tectonic plates slip, there is uplift on one side of the slip, which causes a fault to occur.
Earthquakes are the most common cause of a fault line. Any time two tectonic plates slip, there is uplift on one side of the slip, which causes a fault to occur.
What is a likely event that could cause the igneous intrusion listed as D in the above image?
Answer
When magma rises through the surface, it cuts across the rock already in place. As the magma cools, it leaves behind an intrusion of different rock cutting through the older rock.
These images show that the area surrounding BYU-Idaho’s campus consists primarily of igneous (volcanic) deposits. Briefly list and describe what these rocks indicate about the recent history of the area.
Answer
The presence of igneous rocks indicate the following: tectonic processes in the mantle beneath this area produced magma that rose into the crust and eventually erupted on the surface.
Is it clear to you now how humanity knows this? Observations of many types help geoscientist identify lava (magma) as the source of igneous rocks. These observations include erupting volcanoes and the rocks they produce, laboratory experiments, computer modeling, etc. Once established, the connections between igneous rocks, magma, and the tectonic processes that produce magma can be used to interpret igneous rocks.
The next three questions are about the above image. What does the lower pinkish rock body—the igneous rock (granite)—indicate?
Answer
Igneous rocks indicate that, at the time this rock formed (~2.5 bya) tectonic processes in the mantle beneath the area produced magma that rose into the crust and solidified to form this rock body. The rock would appear pink due to the mineral (most commonly feldspar) that made up the material that formed this rock. This is a good example of how the composition of Earth materials affect the way Earth looks.
What does the erosional surface in the above image indicate?
Answer
The erosional surface indicates a period of active destruction (recycling) of previously formed rock. Elsewhere, the rock bodies that were eroded here are still preserved. These and other observations indicate that about 10 km (about 7 miles) of rock were removed, bringing the granite that had formed in the middle crust to Earth’s surface. Where did those eroded rocks go? They were transported, mostly by water, to the coast and formed sandstones, shales, and limestone.
The detailed attributes of the sandstone that lies atop the granite indicate that it formed in a beach environment. What does the sandstone sitting on the granite indicate about sea level?
Answer
After the period of extended (approximately 2 By) erosion, sea level rose. At this location about 500 Mya, a beach trapped sand that was eroded in the interior of the continent and transported to the shoreline by rivers.
Is it becoming more clear how humanity has pieced together the history of the Earth, a literal record of the events that comprise The Creation, from the formation of Earth to today? We hope so!
In general, what do sedimentary rock bodies indicate about the history of an area?
Answer
Sedimentary rock bodies record the nature of Earth’s surface at the time they formed. For example, they record the locations and characteristics of ancient beaches, streams, and dune fields.
Imagine that the three images below are found directly on top of each other, with the left-most on the bottom and right-most on the top. The image on the left (the Gallatin formation) records an intermediate-depth marine environment, the middle image (of the Tensleep Sandstone) records a continental sand sea or extensive dune field, and the image on the right (Chugwater Formation) records a tidally influenced coastal plain. What does the sequence indicate about changing sea level and depositional environments in this area, during the period when each of these layers formed?
Answer
The succession of intermediate-depth marine environment to continental sand sea (extensive dune field) represents a lowering of sea level, and the subsequent transition to a tidally-dominated shoreline environment indicates a rise in sea level.
Be aware that we’re just discussing the very most basic aspects of what humanity can (and does) learn from these rock bodies. For example, these rock units record important aspects of petroleum production and transport, the history of life on Earth during the time they formed, and information about distant tectonic events that exposed once-deeply-buried rocks to the surface allowing erosion to produce the sediments that formed these rocks.
At Rock Creek Hollow, we observed the tilted and metamorphosed sedimentary rocks shown above. What does the tilt of these sedimentary rocks indicate about the history of this area?
Answer
Sedimentary rocks are comprised of horizontal layers. Thus, the tilt of these sedimentary rocks indicates that tectonic activity changed their original orientation.
As mentioned, these metamorphic rocks were originally sedimentary rocks. What does the metamorphism indicate about the history of this area?
Answer
Sedimentary rocks form at Earth’s surface, and metamorphism occurs deep inside Earth’s crust (at or below about 10 km or around 7 mi). Thus, these metamorphosed sedimentary rocks record a tectonic event that buried these rocks deeply and a subsequent tectonic event the uplifted the crust in this area and caused erosion to re-expose these rocks at Earth’s surface.
For completeness, describe what an observed fault or fault system indicates about the history an area.
Answer
The characteristics of faults record the nature of past tectonic activity—such as its orientation and intensity.
Recording Earth’s Events
Think about how you would identify historical events of our earth.
Watch this video (about 4.5 minutes) to see how we can know the history of a supervolcano in the United States.
