geo hw 11
The _____________ can be used to determine the relative ages of the sedimentary rocks versus canyon formation.
"Principle of Cross Cutting Relationships"
The sedimentary beds were initially deposited in a(n) __________ orientation.
"horizontal"
The sedimentary layers are ____ than both folding and stream incision.
"older"
The_______________says that folded sedimentary beds have been disturbed since deposition.
"Principle of Original Horizontality"
What sort of history do we have here? Below the unconformity we observed rocks that were strongly deformed, metamorphosed, and partially molten; these things all occur deep within the crust. Above the unconformity, we see typical sedimentary rocks that reflect a changing landscape at the surface. Using what we've observed and what you know about different rocks, create a logical sequence of events for the Great Unconformity.
(WRONG) oldest somewhere deep below..... metamorphic-igneous rocks are brought up...... sediments accumulate on exposed..... sediments are buried.... rock uplift and erosion creates..... youngest
Part complete The term ________ refers to life forms intermediate in complexity between early and much later, more modern-looking life forms.
Mesozoic
The Jurassic Period lies in the _____ Era, which was dominated by large terrestrial vertebrates, or _____.
Mesozoic; dinosaurs
The term ________ describes the era of ancient life forms.
Paleozoic
When you are ready, sort the descriptive terms below onto sections taken from the Gigapan image.
left photo: igneous intrusions resistant to weathering right photo: shale prone to weathering sandstone sedimentary bedding
What is the age of Earth accepted by most scientists today?
4.5 billion years
The Principles of ___________ and __________ were used to determine relative ages in the previous question.
Inclusions, Cross-Cutting Relationships
3. The dike dates to the ____________ period.
Tertiary
Paleontology is the study of ________.
ancient life
After four half-lives of decay, what is the ratio of radioactive parent isotope to stable daughter isotope?
1:15
Below are a series of sketches that show rock units organized by color, and traced across valleys with dotted lines. The keys include information on rock types and relative ages. Remember creating a clear and accurate key is important when sketching in the field. Pay special attention to the keys in these drawings when you make your choice. Select the correct sketch below.
4
The ________ is the idea or concept that ancient life forms succeeded each other in a definite, evolutionary pattern and that the contained assemblage of fossils can determine geologic ages of strata.
principle of fossil succession
Percents help us understand how the parts of something, like a pizza slice or a natural event, relate to the entirety of the pie or Earth's history. Calculate the length of time of the following events as a percent of Earth's age. Round the age of Earth to 5 billion years old.
Assume the length of recorded history is 5,000 years. It is correct to say recorded history represents 0.0001 percent of geologic time. Evidence of abundant fossils date back to 540 million years ago. It is correct to say this represents 10.8 percent of geologic time .If human-like ancestors have been around approximately 5 million years, it is correct to say this represents 0.1 percent of geologic time.
Percents help us understand how the parts of something, like a pizza slice or a natural event, relate to the entirety of the pie or Earth's history. Calculate the length of time of the following events as a percent of Earth's age. Round the age of Earth to 5 billion years old.
Assume the length of recorded history is 5,000 years. It is correct to say recorded history represents 0.0001 percent of geologic time. If human-like ancestors have been around approximately 5 million years, it is correct to say this represents 0.1 percent of geologic time. Evidence of abundant fossils date back to 540 million years ago. It is correct to say this represents 10.8 percent of geologic time.
The era known as the "age of mammals" is the ________ era.
Cenozoic
What is the category name for the largest division of time used on the geologic time scale?
Eon
Using principles of relative dating, classify the statements according to whether they are "true," or " false".
False The dike is older than the inclusion. The inclusion formed originally in the sandstone country rock.
Five layers of rock are cut by two faults. Both faults cut through all five layers of rock. Fault A breaks through to the surface, whereas fault B does not. Which of the following statements about faults A and B is most accurate?
Fault A is younger than fault B, and both are younger than the five layers of rock.
What is the principle of cross-cutting relationships?
Geologic features that cut through rocks must form after the rocks that they cut through.
Review the outcrop again. Order the specific locations identified in the outcrop by their age. Note where the arrow, square, and circles are located.
Oldest will be -circle,-square-arrow-Darken circle(youngest age)
Simple yet thoughtful observation exposes the history of an outcrop. The sedimentary rocks in the Gigapan image were formed as sediment accumulated as layers that stacked atop older layers. As layers became lower in the stack sequence and covered by newer layers, they became rocks. If this area had been under water, the shells of organisms would have become limestone, a rock that can't be identified visually but can be identified using field-based tests. Underwater movement of sediment may also create mixes of fine and coarse grains. This sediment becomes conglomerate, a rock clearly identifiable given its combined coarse and fine grains. Over time, some layers would have become exposed as the water retreated and the rock layers above them were eroded. Additionally, some layers would have been tilted by tectonic forces. If this area had been under water, the shells of organisms would have become limestone, a rock that can't be identified visually but can be identified using field-based tests. Underwater movement of sediment may also create mixes of fine and coarse grains. This sediment becomes conglomerate, a rock clearly identifiable given its combined coarse and fine grains. Over time, some layers would have become exposed as the water retreated and the rock layers above them were eroded. Additionally, some layers would have been tilted by tectonic forces. Classify the observations according to the rock that they describe, or choose "Not enough information to tell."
Image 1: Rocks include very thin layers between thicker layers The layers of sedimentary rock are tilted Image 2: A thin layer of conglomerate overlies a sedimentary rock with smaller grain size Layers of sedimentary rock are horizontal Image 3: The rock layers are composed of limestone sediment The thin sedimentary layers formed on the ocean floor
Now that you have identified the unconformity in this outcrop, can you explain why it is an angular unconformity? Review the statements below, and indicate which are correct.
It is an angular unconformity because layers of sedimentary rock are above and below the unconformity and the layers above and below are not parallel. The tilting of the layers of rock occurred before erosion of the unconformity surface.
5. Due to an unconformity, the ___________ period is missing from the rock layer record
Jurassic
Due to an unconformity, the __________ period is missing from the rock layer record.
Jurassic
About 88 percent of geologic time is represented by the time span called the ________ era.
Precambrian
Which of the following principles are key to relative dating? Choose all that apply.
Principle of original horizontality Principle of cross-cutting relationships Law of superposition
A radioactive element undergoes decay via the loss of two alpha particles to form a stable daughter isotope. Following the decay, what would the atomic number of this newly created stable isotope be?
The atomic number of the daughter isotope would be four units less than the original parent isotope.
The principles of relative dating can be used to understand the order of geologic events. A geologic event can be anything: the deposition of horizontal layers of sedimentary rock, the faulting or folding of rock layers, the tilting of rock layers, the erosion (or wearing away) of rock, the intrusion of volcanic rock within existing rock layers, and so on. Refer to these relative dating principles: Inclusions: Any rock fragments included within another rock must be older than the rock in which they are included. (For example, if eroded fragments of one rock layer become part of another sedimentary rock layer, the rock with the included fragments must be younger than the fragments themselves.) The Principle of Cross-cutting Relationships: Any rock or feature cutting through another rock or feature must be younger than the material through which it cuts. (For example, with faults, the first rock must be there for these secondary features, such as igneous intrustions like dikes or fractures, to cut through.) Tilting or deformation could occur to an otherwise horizontally layered sedimentary rock. Most layers of sediment are deposited in a nearly horizontal position. Thus, when we see rock layers that are folded or tilted, we can assume that they must have been moved into that position by crustal disturbances after their deposition. In such an instance, the tilted structure will be younger than the orginal horizontal layers. Order the four images below along the timeline based on the sequence of geologic events.
Rank from oldest to youngest. oldest horizontal layers with ocean water at top layers with inclusions from above and below layers are cut by an igneous dike layers are tilted, erosion of tilted surface youngest
The figure below shows a series of rock layers and a volcanic dike. Rock A is the oldest rock in the sequence. Use the principles of stratigraphy to rank items A-F.
Rank the strata from oldest to youngest. oldest A D C B F E youngest
Which of the following statements about relative and absolute age dating is most accurate?
Relative age dating places rocks and events in chronological order but does not provide information about absolute age.
What is the principle of original horizontality?
Sedimentary rocks are close to horizontal when deposited.
Which principles of relative dating did you use to answer the previous question?
Superposition and Cross-Cutting Relationships
The dike dates to the ___________ period.
Tertiary
Why is the geologic time scale more detailed in the Phanerozoic than in previous eons?
The Phanerozoic Eon is more detailed because of the presence of organisms with hard parts and the rapid increase in biodiversity.
A fault (F) breaks three layers of sedimentary rock (S). An igneous intrusion (I1) has broken through the bottommost layer of rock. A second igneous intrusion (I2) has moved up the fault and pooled on top of the uppermost layer of rock. Which event would be considered the youngest?
The intrusion of I1 or I2 is the youngest event. Without more information, we cannot know which igneous rock is youngest.
Using a calendar year as an analogy to the geologic time scale, when do the oldest anatomically modern humans appear on Earth?
The oldest human fossils show up at about eleven minutes to midnight on December 31st.
Which principle of relative age dating is important for determining the relative age of igneous rock that has intruded into overlying rock?
The principle of cross-cutting relationships.
The tilted rocks must have been most likely tilted during or after the _______ period
Triassic
The tilted rocks must have been most likely tilted during or after the __________ period
Triassic
Using principles of relative dating, classify the statements according to whether they are "true," or " false".
True The sandstone country rock is older than the dike. The intrusive igneous rock making up the dike is the youngest in age.
Name the epoch, period, era and eon in which we currently live.
We live in the Holocene Epoch of the Quaternary Period, which is part of the Cenzoic Era and Phanerozoic Eon.
What is the principle of superposition?
Within a sequence of rock layers formed at Earth's surface, rock layers lower in the sequence are older.
Which of the following organisms would be most likely to be preserved in the geologic record?
a clam with a thick calcite shell that lived on a mudflat
2. The Quaternary and Tertiary rocks are separated by this type of unconformity: ____________
a disconformity.
The Quaternary and Tertiary rocks are separated by this type of unconformity:
a disconformity.
1. The Triassic and Cretaceous rocks are separated by this type of unconformity:_______________
an angular unconformity.
The Triassic and Cretaceous rocks are separated by this type of unconformity:
an angular unconformity.
Choose the location of the unconformity.
arrow straight up second highest
How is the atomic number of an atom determined?
counting the number of protons in the nucleus
Which is an example of radioactivity that occurs when a neutron is converted to a proton and an electron is emitted from the nucleus?
emission of a beta particle
The process of stream _________ is younger compared to the folding of the rock units.
incision
The principle of lateral continuity proposes that sedimentary rock layers continue in all directions until they grade into a different rock type or thin out on the edge of a basin is important because ________.
it allowed geologists to correlate sedimentary rock units over large distances
The principle of cross-cutting relationships which states that a geologic feature that cuts across another feature must be younger than the feature it cuts is important because ________.
it provided a tool for sorting out the relative timing of various geologic events
The principle of horizontality which states that sediments are usually deposited in relatively flat layers is important because ________.
it provided a way to recognize if rocks had been deformed
The principle of superposition which states that in undeformed rocks, the younger rocks will be on top of older rocks, is particularly important because ________.
it provided an order for assembling the relative ages of various rock layers
Below is a geologic structure that illustrates the various principles of relative dating. You will identify the basic principles used in relative geologic dating by dragging labels to their corresponding targets in the image below.
left to right principle of superposition principles of inclusions principle of cross-cutting relationships
Select the drawing that best represents the orientation of rock layers beneath the surface of the formation.
left to right, top to bottom
Where you see layers of sedimentary rock at an angle in contact with rocks that are horizontal, they are separated by a surface called an angular unconformity. This erosion surface represents a time when rocks were eroded before new layers of rock were formed. This can also occur during a pause in deposition, when a period of deformation (such as folding or tilting) has occurred. Choose the sketch that best represents the rock outcrop. Include rocks and sediment packages in your answer.
light pink dark pink tan Geologists use sketches such as this to determine what tectonic forces have shaped the landscape in this area.
Revisit the different definitions for unconformities and then try to classify the Wind River Canyon unconformity. The Great Unconformity is a(n):
nonconformity
Which process is not a common form of natural radioactive decay?
nuclear fission
Use the information from the video and above on relative dating to rank the geologic events and processes from oldest to youngest. Pay particular attention to the sediments and depositional environments for each formation. Rank from oldest to youngest.
oldest CARBONATE SEDIMENTS WERE DEPOSITED IN A SHALLOW sediment was deposited in stream and floodplain..... an abundance of sand was transported and deposited... erosion of the sedimentary layer the sun juna youngest
Petrified wood is an example of a fossil formed by ________.
permineralization replacing original cellulose of the wood
Part complete Which material, principle, or process enables a method of numerical dating?
radioactivity
When looking for fossils, it is important to identify whether fossils are found in the same formation and, thus, may have lived at the same time (or nearly the same time) or if they existed long before or after. Imagine that you have found dinosaur fossils at the location indicated with the star in the section of the Gigapan image below. Sort the other locations to identify whether the locations of the layers indicated by red dots are the same age, younger, or older than the layer indicated by the star (which possesses dinosaur fossils). It will be helful to recall the earlier parts of this exercise where you figured out the geometry and relative ages of these layers.
same age: middle red dot younger age: left side dots older age: right side dots
Geologists collect observations from field sites and then summarize their interpretations. It is your turn to take everything you learned while exploring the rocks in this formation near El Paso, Texas, into a coherent story. Arrange the following geologic events in the order that they occurred.
the layer below the unconformity were deposited the layers below the unconformity were tilted the unconformity surface was created where layers eroded layers above the unconformity were deposited over the eroded layers
The weathering of this outcrop plays an important role in shaping the landscape we see before us today. However, not all rock layers have weathered at the same rate. If they had all eroded at the same rate, the landscape would be a flat plain with no variations. Today's landscape provides evidence that some rock types, especially those that are well cemented together, are more resistant to weathering and erosion than other rock types. Rocks with less resistance are worn away over time, leaving depressions, while more resistant layers tend to form topography and cliff faces. Choose the layer most resistant to weathering and erosion in the section of the Gigapan image shown below.
the middle red dot
It is important to understand how the new landscape came about in order to find clues for the relative ages of rocks in an area. Keeping in mind the principles of geology and understanding the landscape that used to be in this area before weathering wore parts away, choose the oldest layer identified by a red dot in the section of the Gigapan image shown below.
the most left red dot one
The fundamental principle of geology put forth by James Hutton is called _______.
the principle of uniformitarianism
The ________ is the idea or concept that ancient life forms succeeded each other in a definite, evolutionary pattern and that the contained assemblage of fossils can determine geologic ages of strata.
the west of texas
Unconformities that represent a break in the geologic record of deposition are geologically significant ________.
they represent a period of erosion in the region
One of the primary goals of geology is to ________.
understand the history of Earth
Primates have existed for approximately 1.3 percent of geologic time. The Phanerozoic eon, the present Eon, is 10.84 percent of geologic time. Life has existed on Earth approximately 76 percent of geologic time. Label the accompanying geologic time scale for when these historical events began. The labels that you will place on the scale include events in Earth's history and number of years (in millions of years) before present. Round the age of Earth to 5 billion years. Note that the years indicated are millions of years ago. For example, the most recent age on the chart is 65.5 million (65,500,000) years ago. Drag the appropriate labels to their respective targets. You do not need to use all labels.
up first primates appear 542 life starts down
Information about a landscape's past can be revealed by interpreting the characteristics of rocks in an outcrop. Evidence of the direction of processes (e.g., direction of plate movement, folds and faults, mineral foliation, wind and water currents) is especially informative. Imagine standing at the location where the Gigapan image was taken and observing the natural and built features around you. Similar to how you identified the location of this outcrop in Part A, use Google Earth or Google Maps at a multiple zoom levels. Choose the most accurate representation of the outcrop's orientation and your vantage point (where you are standing in relation to the outcrop). The representations below depict your location and the outcrop as viewed from above. The yellow dot is the point where the Gigapan image was taken. Use the map of the outcrop and relative locations of natural and constructed objects (e.g., buildings, roads) to identify the correct representation.
you between north an east outcrop between south and west
The process of stream incision is __________ compared to the folding of the rock units.
younger
