Posted: June 28th, 2022

Subject: Earth Science

Three assignments are attached. Has to be done according to the assignment description. Sources have to be disclosed.
Earth Science Homework
ATTACHED FILE(S)
Atmosphere
Lesson FeedbackCourse Dashboard
· Lesson Objectives
· The student will investigate and understand the origin and evolution of the atmosphere and the interrelationship of geologic processes, biologic processes, and human activities on its composition and dynamics.
· key concepts include scientific evidence for atmospheric changes over geologic time
· current theories related to the effects of early life on the chemical makeup of the atmosphere
· comparison of the Earth’s atmosphere to that of other planets
· atmospheric regulation mechanisms including the effects of density differences and energy transfer
· potential atmospheric compositional changes due to human, biologic, and geologic activity
· What is the atmosphere? What does it do? How was it formed?
Watch this video to give you a preview of what we will learn in this lesson.
Here are 25 Amazing Facts about our atmosphere!
When the Earth was first formed, the gases released by various processes were probably stripped away by the Sun’s solar winds, but eventually a state was reached where the atmosphere remained. This atmosphere would have seemed very thick compared to today’s atmosphere, with about 80% of it made up of water vapor. This water vapor would have been released as rainfall, and created the oceans.
Water sediments have been found that date back as far as 3.8 billion years ago. Studying these sediments can tell us much about the content of the Earth’s atmosphere. Just after our first known early life forms, at about 3.5 billion years ago, the atmosphere seems to have stabilized as a nitrogen rich matter. The balance of living organisms, shifting land masses, and the content of the atmosphere slowly changed until there was an oxygen component to the atmosphere, which grew. Today’s atmosphere is mostly nitrogen (about 78% in dry air) and oxygen (about 21% in dry air), with some other elements, such as carbon, also getting into the mix.
There was a long period of time when Earth’s atmosphere did not contain oxygen. It is theorized that many of the processes where organisms now use oxygen at one time used sulfur instead. Studying the chemical make-up of rock beds can give scientists information about what compositions were available in the air. In the past, there was probably a lot more carbon dioxide in the atmosphere, but since carbon dioxide is water soluble, it gets washed down by rain. Also, plant life uses carbon dioxide during photo-synthesis, and releases oxygen, which helps explain the growing oxygen component.
Unlike several of our neighboring planets, the Earth’s atmosphere has a way of balancing the amount of carbon dioxide in the atmosphere: The carbon cycle, or the carbon-silicate cycle. As rain falls, it pulls carbon dioxide from the air and deposits it into the oceans. Sea creatures use the carbon (usually in combination with calcium and other minerals) and then when sea creatures die, the carbon compounds wind up as sediment at the bottom of the ocean. The ocean floor is seismically active, which brings these compounds into the mantle, where they can be re-released only by volcanic activity.
Atmospheric Layering
The atmosphere has five distinct layers, each with different chemical compositions, different temperatures, and different densities. The layers are known as the troposphere, the stratosphere, the mesosphere, the thermosphere, and the exosphere.
The troposphere is the layer closest to the ground. It extends about 12 miles above the Earth’s surface at the equator, but only about 4 miles above the Earth’s surface at the poles. The troposphere has the right composition, pressure, and temperatures to make life on Earth (as we know it) possible. The further away from the Earth one goes, or the higher the elevation, the thinner and colder the air gets. Since the air is colder up higher, and heat rises, this means that there is likely to be a lot of air movement in this layer. It is also where all weather takes place.
See the different layers of the atmosphere and what each one does:
Volcanic Effects
As mentioned earlier with the carbon-silicate cycle, magma is one repository of dissolved gases. It is also one of our largest sources of water. Magma is compacted into an extremely dense state under the surface of the Earth, such that when it is explosively released it takes up much more space on the surface of the Earth than it does underground. According to the U.S. Geological Survey, “if one cubic meter of 900°C rhyolite magma containing five percent by weight of dissolved water” were brought up to the surface in an instant, that “one cubic meter of magma now would occupy a volume of 670 m3as a mixture of water vapor and magma at atmospheric pressure.”
The biggest release from a volcanic eruption is that of water vapor, but there can also be large amounts of carbon dioxide and sulfur dioxide. Aside from the immediate dangers of eruptions, scientists have found that volcanic eruptions can also affect climate.
“Measurements from recent eruptions such as Mount St. Helens, Washington (1980), El Chichon, Mexico (1982), and Mount Pinatubo, Philippines (1991), clearly show the importance of sulfur aerosols in modifying climate, warming the stratosphere, and cooling the troposphere. Research has also shown that the liquid drops of sulfuric acid promote the destruction of the Earth’s ozone layer.” (USGS, “Volanic Gases and Their Effects”)
The Human Factor
There has been some concern over the effect that human activity can have on the atmosphere. Modern man has developed many technological advances that release gases into the atmosphere that would otherwise not be present, or release gases in greater quantities than would otherwise occur. If this has an effect on the climate of the Earth it could be dangerous, over the long term, to the delicate balances that support life.
“Scientists have calculated that volcanoes emit between about 130-230 million tonnes (145-255 million tons) of CO2into the atmosphere every year (Gerlach, 1999, 1991). This estimate includes both subaerial and submarine volcanoes, about in equal amounts. Emissions of CO2by human activities, including fossil fuel burning, cement production, and gas flaring, amount to about 27 billion tonnes per year (30 billion tons) [ ( Marland, et al., 2006) – The reference gives the amount of released carbon (C), rather than CO2, through 2003.]. Human activities release more than 130 times the amount of CO2emitted by volcanoes–the equivalent of more than 8,000 additional volcanoes like Kilauea (Kilauea emits about 3.3 million tonnes/year)! (Gerlach et. al., 2002).” (USGS, “Volanic Gases and Their Effects”)
For more info:https://volcanoes.usgs.gov/vhp/gas_climate.html
___________________________________________________________________________________________
Bonus Content (This section is not required)
If you are interested in more information about some of the topics from the lesson OR if you need help with some of the questions, you can watch these
OPTIONAL(you can watch if you want but they are not required) v
ideos for help!
See what the formation of the atmosphere might have looked like:
How does the earth’s atmosphere compare to the other planets in our solar system?
Venus
Mars
The Outer Planets
What does the atmosphere do?
Why is there life on earth? What does this have to do with Goldilocks?
See how heat is transferred in the atmosphere through convection currents:
What is air pressure, how is the uneven heating of the atmosphere important, and how does it impactweather?
What do humans do to impactthe atmosphere?
What happens if Earth loses its atmosphere?
· Grading Rubric
Rubric Earth Science Lesson 10
Note: For this class it is necessary to post each question, then the work/explanation, then the answer. Failure to do so will result in asking for a revision. No grade will be given for incomplete work.
Mastery of this lesson will be determined when your total points are 8 or higher. Revisions will be requested when your total points are below 8. Points are earned according to the chart below.
10: A total score of 10 on your first submission, or within the first revision.
9.5: A total score of 9.5, or all questions are correct after the first revision.
9:A total score of 9.
8.5: A total score of 8.5.
8:A total score of 8.

Short answer
Total content points= 8

All parts of all questions are answered in complete sentences.
1 points each

Questions are answered in complete sentences. Not all parts of each question are answered.
0.5points each

Questions are not answered in complete sentences and/or are missing responses for questions.
0 points

Apply Your Knowledge
Total content points=2

Questions are thoroughly answered in complete sentences and in the student’s own words. URLs are included for outside research.
1 point each

Questions are answered but may have incomplete responses or contain minor errors. Responses are in the student’s own words. URLs are included for outside research.
0.5 points each

Questions contain inaccurate information and/or are not written in the student’s own words. URLs for outside research are not provided.
0 points
· Assignment
Do not submit text that you have copied from sources, including websites. All of your work should be in your own words. Using copied text would be considered plagiarism. For more information, review our page on
Plagiarism and Citation
. Cite the complete web page source under each answer. Always put the question on top of the answer, and answer in complete grammatically correct sentences.
Many of these answers will require Internet research to answer. Make sure you rewrite all answers into your own words and be mindful of our page on
Plagiarism and Citation
.
Short Answer
1. Find out a little more about the layers of the atmosphere.
a. Which layer is the largest? How large is it?
b. Where is the ozone layer located? Why is the ozone layer important?
c. What is the outermost layer called? About how far above the Earth does it reach?
2. What is the atmosphere of Venus like, and how does it compare with Earth’s atmosphere?
3. What is the atmosphere of Mars like, and how does it compare with Earth’s atmosphere?
4. How are the atmospheres of the inner planets different from the atmospheres of the gas giants?
5. What is the “Goldilocks Effect” when discussing Earth?
6. One important thing that happens in Earth’s atmosphere is known as heat transfer. In this context, find out what convection is and tell me briefly about it here. Explain why this movement occurs.
7. About what percentage of the atmosphere is made up of water vapor today?
8. What is atmospheric pressure?
Apply Your Knowledge
9. What does it mean when barometric pressures rise and fall? What is the weather like when it rises? What is the weather like when it falls?
10. Name two things humans can do to minimize the impact their technologies have on the atmosphere.
Начало формы
Nonrenewable and Renewable Resources
Lesson FeedbackCourse Dashboard
· Lesson Objectives
· The student will investigate and understand the differences between renewable and nonrenewable resources.
· key concepts include fossil fuels, minerals, rocks, water, and vegetation
· advantages and disadvantages of various energy sources
· resources found in Virginia
· making informed judgments related to resource use and its effects on Earth systems
· environmental costs and benefits.
·
To support the way human beings live, it is necessary to use certain resources in the environment. When these resources cannot be replenished in a short amount of time, they are referred to as nonrenewable resources. Resources whichcanbe replenished in a short amount of time are called renewable resources.
Nonrenewable Resources
The resources most commonly considered “nonrenewable” are oil, natural gas, coal, and uranium. Fossil fuels (oil/petroleum, natural gas/propane, coal) can take millions of years to form, and at current rates will be depleted long before any more will form. Uranium is not a fossil fuel, but the special kind used in nuclear plants is very rare.
See the difference between Nonrenewable and Renewable Resources
Power plants which run off of nonrenewable resources use the nonrenewable resource to generate heat. The heat is used to boil water, which turns a turbine, and the turbine generates electricity.
Fossil fuels were formed from organic material which was deposited on the bottom of the ocean floor a long time ago, millions of years before the dinosaurs. This organic material became part of the sedimentary rock, and as more layers were added and the pressure on top built high enough to create intense heat these organic materials went through chemical changes, becoming different sorts of carbon based solids, liquids, and gases.
Oil
In most places, the organic materials that were trapped under the sediment layers were heated for millions of years until they formed into a thick, black liquid called oil. This oil seeped toward the surface, but was sometimes stopped by layers of impermeable stone. These layers of stone are called “capstones”, and it is under these capstones that we find pockets of oil today.
The top five oil producing states are Texas, Alaska, California, Louisiana and Oklahoma. However the U.S. has only been producing about 40% of the oil it needs, so the majority of oil is imported. In 2000, the U.S. spent 109 billion dollars on importing oil.
Oil is used to make heating oil, as well as gasoline, diesel, and jet fuel. Oil is also used in the making of some plastics and other products (such as crayons and bubble gum).
This video shows how oil and natural gas are formed:
Natural Gas
In some places when oil formed the heat and pressure continued to build until that liquid was transformed into a gas. This natural gas did much as the oil did, and found ways to seep to the surface. However, again like the oil, this gas was stopped by capstones, which is where we find natural gas today.
Natural gas is an odorless flammable gas, most often used for heating homes.
Coal
Coal is a combustable solid which is mined from the ground. Coal formed much the same way as the oil and gas did, though it is thought that sulfurous seas covered the vegetation and mixed into the base organic materials, adding some extra elements to the process. As pressure is applied over time by the layers of rock above it, coal goes through many stages of development first forming peat, then lignite (brown coal), then sub-bituminous, bituminous and anthracite coal. The pinnacle of coal evolution is graphite, but it is not used as a fuel since it is hard to ignite.
Coal may be the biggest fossil fuel in the United States. It is relatively inexpensive: 23 of the 25 U.S. power plants with the lowest operating costs are using coal. Coal based plants are responsible for over half of the U.S. electrical power. Also, the U.S. has plenty of coal; it is estimated that the U.S. could produce energy for itself for at least another 200 years using the coal reserves in the U.S. However coal has tremendous negative environmental impacts, from dangerous and damaging mining methods to the smoke (containing sulfur and carbon dioxide) which is released when it is burned.
Coal has been mined in 26 of the 50 states in the U.S., but the four states with the largest coal reserves are: Wyoming, West Virginia, Illinois, and Montana.
Coal in the United States
According to the Energy Information Administration, a division of the U.S. Dept. of Energy, there are three main coal producing regions of the U.S.:
Appalachian Coal Region:
Interior Coal Region:
Western Coal Region:
* Over half of the coal produced in the U.S. is produced in the Western Coal Region.
* Wyoming is the largest regional coal producer, as well as the largest coal-producing state in the nation.
* Large surface mines.
* Some of the largest coal mines in the world.
· * More than one-third of the coal produced in the U.S. is produced in the Appalachian Coal Region.
* West Virginia is the largest coal-producing state in the region, and the second largest coal-producing state in the U.S.
* Large underground mines and small surface mines.
* Coal mined in the Appalachian coal region is primarily used for steam generation for electricity, metal production, and for export.
* Texas is the largest coal producer in the Interior Coal Region, accounting for almost one-third of the region’s coal production.
* Mid-sized surface mines.
* Mid- to large-sized companies.
Uranium
Uranium is a relatively abundant element, but only a particular kind of uranium (U-235) is used in nuclear power plants. This type of uranium has atoms which are more easily split apart, and it is in splitting these atoms that energy is released. The majority of uranium in the U.S. in mined in the western states. It provides about 19% of the power in the U.S.
According to EIA, after processing “[t]he uranium fuel is formed into ceramic pellets. The pellets are about the size of your fingertip, but each one produces the same amount of energy as 150 gallons of oil.”
Compared to fossil fuels, uranium is a clean fuel. It still produces waste, however, some of which is mildly radioactive.
Renewable Resources
When speaking of renewable resources, mostly people are referring to wind, solar, biomass, geothermal, and hydro power. You will be asked to research and discuss several of these in the assignment below.
Given that we know nonrenewable resources are limited, why don’t we use more renewable energy? According to the U.S. DOE:
In the past, renewable energy has generally been more expensive to use than fossil fuels. Plus, renewable resources are often located [in] remote areas and it is expensive to build powerlines to the cities where they are needed. The use of renewable sources is also limited by the fact that they are not always available (for example, cloudy days reduce solar energy, calm days mean no wind blows to drive wind turbines, droughts reduce water availability to produce hydroelectricity).
The production and use of renewable fuels has grown more quickly in recent years due to higher prices for oil and natural gas, and a number of State and Federal Government incentives, including the Energy Policy Acts of 2002 and 2005. The use of renewable fuels is expected to continue to grow over the next 30 years, although we will still rely on non-renewable fuels to meet most of our energy needs.
One of the larger prices attached to renewable energy resources is the price of land. Wind farms take many acres of land in order to produce energy. Horse Hollow Wind Energy Center in Texas is the world’s largest wind farm, it has 421 wind turbines which can power 220,000 homes per year; this wind farm takes up nearly 47,000 acres. Solar cells have a similar problem, since the sun’s rays only deliver a small amount of energy to any single spot: It is the energy collected over a wide area which makes the technology useful. Despite large land or space needs, however, there are fewer environmental impacts from renewable energy resources than tend to exist from nonrenewable ones.
Other Resources and Sustainability
Generally renewable and nonrenewable resources are discussed in reference to energy production. However there are many other renewable and nonrenewable resources. For example, the fish in a bay would be an important, potentially renewable, food resource. Any mineral in an area might be an important nonrenewable resource: This could be tin, silver, gold, diamonds, salt, limestone…the list is almost endless. Any item in an area can be assessed as renewable or nonrenewable based on the method of its extraction, the rate of use, and the rate of replenishment. For example, if we timber land for lumber, but do so at a rate that leaves us with no more trees before we’ve met our need for lumber, this is not sustainable (hence, not a renewable resource, even though we can grow more trees).
Being aware of whether a resource is renewable or not is only a part of responsible resource management. A nonrenewable resource may be extracted and used responsibly, and a renewable resource can be extracted in ways that are a nuisance: New studies are often being conducted to give us information on how to best utilize these resources the Earth grants us.
___________________________________________________________________________________________
Bonus Content (This section is not required)
If you are interested in more information about some of the topics from the lesson OR if you need help with some of the questions, you can watch these
OPTIONAL(you can watch if you want but they are not required) v
ideos for help!
Watch this video to see how coal is formed and the different types of coal.
Check out these facts about Uranium
See how biomass energy works:
This video discusses how geothermal energy works:
See how a dam creates energy through hydropower:
· Grading Rubric
Rubric Earth Science Lesson 9
Note: For this class it is necessary to post each question, then the work/explanation, then the answer. Failure to do so will result in asking for a revision. No grade will be given for incomplete work.
Mastery of this lesson will be determined when your total points are 8 or higher. Revisions will be requested when your total points are below 8. Points are earned according to the chart below.
10: A total score of 10 on your first submission, or within the first revision.
9.5: A total score of 9.5, or all questions are correct after the first revision.
9:A total score of 9.
8.5: A total score of 8.5.
8:A total score of 8.

Short Answer
4 points total

Answer is clearly written and accurate. Answer is based on the lesson content.
0.5 points

Answer is clearly written. May have 1 factual omission or error.
0.25 points

Answer is not clearly written. There are several factual omissions or errors.
0 points

Apply Your Knowledge Questions
6 points total

Questions are thoroughly answered in complete sentences and in student’s own words. URLs are included for outside research.
1 points

Questions are answered but may have incomplete responses or contain minor errors. Responses are in the student’s own words. URLs are included for outside research.
0.5 points

Questions contain inaccurate information and/or are not written in the student’s own words. URLs for outside research are not provided.
0 points
· Assignment
Do not submit text that you have copied from sources, including websites. All of your work should be in your own words. Using copied text would be considered plagiarism. For more information, review our page on
Plagiarism and Citation
. Cite the complete web page source under each answer. Always put the question on top of the answer, and answer in complete grammatically correct sentences.
Short Answer
Many of these answers will require Internet research to answer. Make sure you rewrite all answers into your own words and be mindful of our page on
Plagiarism and Citation
.
1. If fossil fuels are formed from organic materials compacted on the ocean floor, what does that tell us about the Appalachian mountain region? What was in the Appalachian region at one point in time to form fossil fuels?
2. What are three of the top oil producing countries of the world?
3. From what you’ve learned about the formation of oil, where are there most likely to be pockets of undiscovered oil today? Add reasonswhy you think oil will be found in that place based on where/how oil is formed.
4. Which fossil fuel is the most abundant in the U.S.?
5. Find four products that are made from oil (petroleum) and list them here. Cite your sources.
6. What do the machines known as “digesters” do?
7. If natural gas is odorless, why is it possible to smell when a house has a gas leak?
8. What is propane? What are some of its uses?
Apply Your Knowledge
9. Why is coal’s release of sulfur and carbon dioxide potentially dangerous?
10. The lesson mentioned that wind farms need a lot of land. What is another negative impact wind farms can have?
11. Can cattle or other livestock graze on the land where a windfarm is located?
12. Hydropower uses the flow of a river or the ebb and flow of the tides to create energy. Tell me about one specific way we capture hydropower. Cite your source.
13. What is geothermal energy?
14. Give me a specific way in which geothermal energy can be harnessed. Cite your source.
Начало формы
Fossils
Lesson FeedbackCourse Dashboard
· Lesson Objectives
· The student will investigate and understand the rock cycle as it relates to the origin and transformation of rock types and how to identify common rock types based on mineral composition and textures.
· Key concepts include sedimentary (clastic and chemical) rocks, scales, diagrams, maps, charts, graphs, tables, and profiles are constructed and interpreted.
· The student will investigate and understand that many aspects of the history and evolution of the Earth and life can be inferred by studying rocks and fossils.
· Key concepts include traces and remains of ancient, often extinct, life are preserved by various means in many sedimentary rocks, superposition, cross-cutting relationships, index fossils, and radioactive decay are methods of dating bodies of rock, absolute and relative dating have different applications but can be used together to determine the age of rocks and structures; and rocks and fossils from many different geologic periods and epochs are found in Virginia.
·
Geological Time
When we look at human history, we often talk about things in terms of hundreds or thousands of years. During the majority of this time we have some sort of written records to analyze. When we talk about looking at the history of the Earth, and the evolution of organisms on it, we are looking at time periods spanning millions and billions of years. Understanding this portion of history requires detective work: gathering evidence and making comparisons.
People who study this kind of history have to use a greater time scale than that used for human history; this time scale is referred to as thegeologic time scale. Think of it like a book, with the rocks as its pages. Some of the pages are torn or missing, and the pages are not numbered, but geology gives us the tools to help us read this book.
Long before geologists had the means to recognize and express time in numbers of years before the present, they developed the geologic time scale. This time scale was developed gradually, mostly in Europe, over the eighteenth and nineteenth centuries. Earth’s history is subdivided intoeons, which are subdivided intoeras, which are subdivided intoperiods, which are subdivided intoepochs. The names of these subdivisions, like Paleozoic or Cenozoic, may look daunting, but to the geologist there are clues in some of the words. For example,zoicrefers to animal life, andpaleomeans ancient,mesomeans middle, andcenomeans recent. So the relative order of the three youngest eras, first Paleoozoic, then Mesozoic, then Cenoozoic, is straightforward.
Fossils are the recognizable remains, such as bones, shells, or leaves, or other evidence, such as tracks, burrows, or impressions, of past life on Earth. Scientists who study fossils are calledpaleontologists. Remember thatpaleomeans ancient; so a paleontologist studies ancient forms of life. Fossils are fundamental to the geologic time scale. The names of most of the eons and eras end in zoic, because these time intervals are often recognized on the basis of animal life. Rocks formed during the Proterozoic Eon may have fossils of relative simple organisms, such as bacteria, algae, and wormlike animals. Rocks formed during the Phanerozoic Eon may have fossils of complex animals and plants such as dinosaurs, mammals, and trees.
This video shows what the earth was like during the Pre-Cambrian. Notice how simple the life forms were and where they all were found:
Now let’s compare what life looks likethroughout the Phanerozoic Eon. Notice how life changes.
Sedimentary Rocks
Most of the rocks exposed at the surface of Earth aresedimentary–formed from particles of older rocks that have been broken apart by water or wind. The gravel, sand, and mud settle to the bottom in rivers, lakes, and oceans. These sedimentary particles may bury living and dead animals and plants on the lake or sea bottom. With the passage of time and the accumulation of more particles, and often with chemical changes, the sediments at the bottom of the pile become rock. Gravel becomes a rock called conglomerate, sand becomes sandstone, mud becomes mudstone or shale, and the animal skeletons and plant pieces can become fossils.
As early as the mid-1600’s, the Danish scientist Nicholas Steno studied the relative positions of sedimentary rocks. He found that solid particles settle from a fluid according to their relative weight or size. The largest, or heaviest, settle first, and the smallest, or lightest, settle last. Slight changes in particle size or composition result in the formation of layers, also called beds, in the rock. Layering, or bedding, is the most obvious feature of sedimentary rocks.
Sedimentary rocks are formed particle by particle and bed by bed, and the layers are piled one on top of the other. Thus, in any sequence of layered rocks, a given bed must be older than any bed on top of it. ThisLaw of Superpositionis fundamental to the interpretation of Earth history, because at any one location it indicates the relative ages of rock layers and the fossils in them.
Layered rocks form when particles settle from water or air. Steno’sLaw of Original Horizontalitystates that most sediments, when originally formed, were laid down horizontally. However, many layered rocks are no longer horizontal. Because of the Law of Original Horizontality, we know that sedimentary rocks that are not horizontal either were formed in special ways or, more often, were moved from their horizontal position by later events, such as tilting through plate tectonics or earthquakes.
Rock layers are also called strata (the plural form of the Latin word stratum), andstratigraphyis the science of strata. Stratigraphy deals with all the characteristics of layered rocks; it includes the study of how these rocks relate to time.
This video shows how we use relative age to date rock layers:
More on the Time Scale
How can we add numbers to a time scale based on rock sediment? How have geologists determined that:
· Earth is about 4.6 billion years old?
· The oldest known fossils are from rocks that were deposited about 3.5 billion years ago?
· The first abundant shelly fossils occur in rocks that are about 570 million years old?
· The last ice age ended about 10,000 ago?
·

Geologic time scale showing both relative and numeric ages.
Ages in millions of years are approximate
Nineteenth-century geologists and paleontologists believed that Earth was quite old, but they had only crude ways of estimating just how old. The assignment of ages of rocks in thousands, millions, and billions of years was made possible by the discovery of radioactivity.

Now we can use minerals that contain naturally occurring radioactive elements to calculate the numeric age of a rock in years.
As you know, the basic unit of each chemical element is the atom. An atom consists of a central nucleus, which contains protons and neutrons, surrounded by a cloud of electrons.
Isotopes
of an element are atoms that differ from one another only in the number of neutrons in the nucleus. For example, radioactive atoms of the element potassium have 19 protons and 21 neutrons in the nucleus (potassium 40); other atoms of potassium have 19 protons and 20 or 22 neutrons (potassium 39 and potassium 41). A radioactive isotope (the parent) of one chemical element naturally converts to a stable isotope (the daughter) of another chemical element by undergoing changes in the nucleus.
The change from parent to daughter happens at a constant rate, called the
half-life
. The half-life of a radioactive isotope is the length of time required for exactly one-half of the parent atoms to decay to daughter atoms. Each radioactive isotope has its own unique half-life. Precise laboratory measurements of the number of remaining atoms of the parent and the number of atoms of the new daughter produced are used to compute the age of the rock. For dating geologic materials, four parent/daughter decay series are especially useful: carbon to nitrogen, potassium to argon, rubidium to strontium, and uranium to lead. Age determinations using radioactive isotopes are subject to relatively small errors in measurement–but errors that look small can mean many years or millions of years. If the measurements have an error of 1 percent, for example, an age determination of 100 million years could actually be wrong by a million years too low or too high.

Parents and daughters for some isotopes commonly used to establish numeric ages of rocks.

Isotopic techniques are used to measure the time at which a particular mineral within a rock was formed. To allow us to assign numeric ages to the geologic time scale, a rock that can be dated isotopically is found together with rocks that can be assigned relative ages because of their fossils. Many samples, usually from several different places, must be studied before assigning a numeric age to a boundary on the geologic time scale.
This video explains how we find the absolute age of a rock or fossil using half-life:
The geologic time scale is the product of many years of detective work, as well as a variety of dating techniques not discussed here. The details will change as more and better information and tools become available. Many scientists have contributed and continue to contribute to the refinement of the geologic time scale as they study the fossils and the rocks, and the chemical and physical properties of the materials of which Earth is made.
Fossil Succession
When most people think of fossils, they tend to think of dinosaurs, but dinosaurs only form a small fraction of the millions of species that live and have lived on Earth. The great bulk of the fossil record is dominated by fossils of animals with shells and microscopic remains of plants and animals, and these remains are widespread in sedimentary rocks. It is these fossils that are studied by most paleontologists.
Three concepts are important in the study and use of fossils:
(1) Fossils represent the remains of once-living organisms.
(2) Most fossils are the remains of extinct organisms; that is, they belong to species that are no longer living anywhere on Earth.
(3) The kinds of fossils found in rocks of different ages differ because life on Earth has changed through time.
If we begin at the present and examine older and older layers of rock, we will come to a level where no fossils of humans are present. If we continue backwards in time, we will successively come to levels where no fossils of flowering plants are present, no birds, no mammals, no reptiles, no four-footed vertebrates, no land plants, no fishes, no shells, and no animals. The three concepts are summarized in the general principle called theLaw of Fossil Succession: The kinds of animals and plants found as fossils change through time. When we find the same kinds of fossils in rocks from different places, we know that the rocks are the same age.
The Law of Fossil Succession is very important to geologists who need to know the ages of the rocks they are studying. The fossils present in a rock exposure or in a core hole can be used to determine the ages of rocks very precisely. Detailed studies of many rocks from many places reveal that some fossils have a short, well-known time of existence. These useful fossils are calledindex fossils.
Today the animals and plants that live in the ocean are very different from those that live on land, and the animals and plants that live in one part of the ocean or on one part of the land are very different from those in other parts. Similarly, fossil animals and plants from different environments are different. It becomes a challenge to recognize rocks of the same age when one rock was deposited on land and another was deposited in the deep ocean. Scientists must study the fossils from a variety of environments to build a complete picture of the animals and plants that were living at a particular time in the past.
If we look at the Law of Fossil Succession together with the concept of evolution, we see that first there were simple single celled organisms, then more complex organisms, then movement from the oceans onto land by both plants and animals, then formation of larger animals on land. We can study the transitions of evolution through studying the fossil record–though the record will not always be complete.
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Bonus Content (This section is not required)
If you are interested in more information about some of the topics from the lesson OR if you need help with some of the questions, you can watch these
OPTIONAL(you can watch if you want but they are not required) v
ideos for help!
Watch the following videosto find out more information on what life was like during thePaleozoic, Mesozoic, and Cenozoictime periods.
Paleozoic Life
Mesozoic Life
Cenozoic Life (Time period we are in right now)
· Grading Rubric
Rubric Earth Science Lesson 8
Note: For this class it is necessary to post each question, then the work/explanation, then the answer. Failure to do so will result in asking for a revision. No grade will be given for incomplete work.
Mastery of this lesson will be determined when your total points are 8 or higher. Revisions will be requested when your total points are below 8. Points are earned according to the chart below.
10: A total score of 10 on your first submission, or within the first revision.
9.5: A total score of 9.5, or all questions are correct after the first revision.
9:A total score of 9.
8.5: A total score of 8.5.
8:A total score of 8.

Short Answer
5 points total

Answers are clearly written, accurate, and student uses their own words.
1 points awarded

Answer is clearly written. May have 1 factual omission or error.
0.5 point awarded

Answer is not clearly written. There are several factual omissions or errors.
0 points awarded

Apply Your Knowedge
3 points total
(1 point per question)

Questions are thoroughly answered in complete sentences and in student’s own words. URLs are included for outside research.
1 point awarded

Questions are answered but may have incomplete responses or contain minor errors. Responses are in the student’s own words. URLs are included for outside research.
0.5 point awarded

Questions contain inaccurate information and/or are not written in the student’s own words. URLs for outside research are not provided.
0 points awarded

Essay
2 points total

Question is answered thoroughly describing how the meteor killed the dinosaurs and at least 2 pieces of evidence are provided.
2 points awarded

Question is answered partially and/or one piece of evidence is missing.
1 point awarded

Question is not answered thoroughly and evidence is not provided.
0 points awarded
· Assignment
Do not submit text that you have copied from sources, including websites. All of your work should be in your own words. Using copied text would be considered plagiarism. For more information, review our page on Plagiarism and Citation. Cite the complete web page source under each answer.Always put the question on top of the answer, and answer in complete grammatically correct sentences.
Many of these answers will require Internet research to answer. Make sure you rewrite all answers into your own words and be mindful of our page on
Plagiarism and Citation
.
Short Answer
1. How are sedimentary rocks formed?
2. Why are fossils found in sedimentary rocks instead of other rock types? Why can’t they be found in igneous or metamorphic?
3. How are radioactive isotopes used to determine the age of rock? Use the word half life in your answer. Explain how it works.
4. How can the Law of Superposition tell us how old one fossil is compared to another found in the same general area?
5. What are fossils?
Apply Your Knowledge
6. What are index fossils? Give at least 2 characteristics of index fossils.
7. What Cenozoic fossils have been found in the region where you live? Name at least two and the location where they were found. Remember Cenozoic is the time period we are in right now. Be sure you cite your source.
8. What Mesozoic fossils have been found in the region where you live? Name at least two and the location where they were found. Be sure you cite your source.
Essay
9. Write a paragraph about the asteroid theory of dinosaur extinction. Be sure to include atleast 2pieces of evidence to support this idea–Make sure to use iridium as one piece of evidence & explain why it is so important.

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