Earth Science
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The Scientific Method
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The scientific method is a process that is used to find answers to questions about the world around us. There are several versions of the scientific method. Some have more steps, while others have only a few. Even though these elements can be used in an ordered manner, they do not have to follow the same order. It is better to think of the scientific method as fluid process that can take different paths depending on the situation. Just be sure to incorporate all of the elements when seeking unbiased answers.
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In order to test a hypothesis, an experiment needs to be conducted. The following are important elements to consider when designing an experiment:
- Control - A group that is similar to other groups but is left alone so that it can be compared to see what happened to the other groups that are tested.
- Data - the numbers and measurements you get from the test in a scientific experiment.
- Variable- Something that can cause something you are testing to change. There are several kinds of variables.
- Independent variable - a variable that you change as part of your experiment. It is important to only change one independent variable for each experiment.
- Dependent variable - a variable that changes when the independent variable is changed.
- Controlled Variable - these are variables that you never change in your experiment.
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Earth's Structure & Plate Tectonics
Earth is made up of four layers, and each layer has unique characteristics. Read about each layer here.
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CRUST: The crust is the outermost layer of Earth. This layer, on which life exists, is covered with soil, rock, and water. Relative to the thickness of Earth’s other layers, Earth’s crust can be compared in thickness to the shell of an egg or the skin of an apple. The crust is thickest under the continents and thinnest under the oceans. Thickness: 5 to 64 kilometers (varies depending on which type of crust) State: Solid |
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MANTLE:
The mantle is Earth’s thickest layer. About 80% of the volume of Earth is contained in Earth’s mantle, which extends from the base of the crust to the liquid outer core. The mantle is generally considered to exist in a solid state, although high temperatures and pressure can cause some of this solid rock to flow like an extremely thick liquid. Thickness: About 2900 kilometers State: Considered solid, but has the quality of plasticity, which means the solid rock in this layer can flow like a thick liquid |
Download "Structure of the Earth" and then answer the questions here:
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OUTER CORE:
Most of the rock in Earth’s outer core is molten, which means that it acts like a hot liquid. The outer core begins about 2900 kilometers below Earth’s surface. Thickness: About 2250 kilometers State: Molten liquid INNER CORE: Earth’s inner core is incredibly dense, because it is under so much pressure. The inner core begins at a depth of about 5,150 kilometers below Earth’s surface. Thickness: Radius is about 1300 kilometers State: Solid |
Watch this video to learn about plate tectonics. and then see how natural disasters like volcanoes and earthquakes are influenced by the movement of plate tectonics on this map.
Download practice GED questions about Earth's structure and plate tectonics below:
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The theory of plate tectonics explains phenomena of Earth's crust: seafloor spreading, the formation of major landforms, and the movement of continents. According to this theory, Earth's crust is made up of tectonic plates that fit together like a crude jigsaw puzzle. These plates move relative to one another at a rate of up to 15 centimeters a ear. At the boundaries between plates, major landforms such as mountain ranges, volcanoes, ocean trenches, and mid-ocean ridges form, and earthquakes occur. There are three types of plate boundaries, or margins. Read about plate tectonics here.
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At conservative, or transform margins, two plates slide by one another, and no crust is created or destroyed. For example, the San Andreas fault in California is the boundary between the North American plate and the Pacific plate, which is sliding northwest, causing many earthquakes. At constructive margins, two plates are moving apart and new crust is forming. Molten material from the mantle below wells up in the space between the plates, hardens, and forms new crust, usually at a mid-ocean ridge. For example, at the Mid-Atlantic Ridge, new crust is forming, causing the seafloor to spread and grow by about 5 centimeters a year. At destructive margins, two plates are colliding and crust is being destroyed. When a continental plate collides with an oceanic plate, the denser oceanic crust may be forced under the other plate, forming a deep trench. When two plates consisting of continental crust collide, the crust crumples to form mountain ranges such as the Andes. |
As plates move, they carry the continents with them. Scientists believe that a single large continent, Pangaea, existed about 250 million years ago. It gradually broke apart, and over millions of years the pieces (which are today's continents) drifted into the locations they are in today.
Rocks & FossilsRocks are all around us. They make up the backbones of hills and mountains and the foundations of plains and valleys. Beneath the soil you walk on and the deep layers of soft mud that cover the ocean basins is a basement of hard rock.
Rocks are made up of different minerals, broken pieces of crystals, or broken pieces of rocks. Some rocks are made of the shells of once-living animals, or of compressed pieces of plants. What a rock is made of, the shapes of the grains, and how the grains fit together all provide valuable clues to help us unlock the rock's history hidden within. Rocks are divided into three basic types depending on how they were formed: Igneous, Metamorphic, and Sedimentary. Igneous rocks are “fire-born,” meaning that they are formed from the cooling and solidification of molten (melted) rock. Molten rock material is known as magma until it is erupted onto the surface when it then is termed lava. Igneous rocks are classified into two groups: Intrusive (plutonic) rocks, which solidify within the Earth, and Extrusive (volcanic) rocks, which are erupted onto the surface or into the atmosphere. Metamorphic rocks form when high temperatures and pressure act on a rock to alter its physical and chemical properties (metamorphism means 'to change form'). These conditions often stretch, twist and fold the rock as it cools. In metamorphic rocks some or all of the minerals in the original rock are replaced, atom by atom, to form new minerals. Sedimentary rocks are formed from deposits of pre-existing rocks or pieces of once-living organism that accumulate on the Earth's surface. If sediment is buried deeply, it becomes compacted and cemented, forming sedimentary rock. These rocks often have distinctive layering or bedding. |
Watch the video to learn more about the types of rocks, and download the practice GED questions to test your knowledge of rocks and fossils here:
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The rock cycle describes the processes through which the three main rock types (igneous, metamorphic, and sedimentary) transform from one type into another. The formation and transformation of the various rock types can take many paths through the rock cycle depending on environmental conditions, as shown in the diagram below:
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Fossils are any preserved remains, impressions, or traces of once-living organisms. Fossils could include bones, shells, stone imprints of animals, objects preserved in amber, petrified wood or DNA remnants. The fossils of bones, teeth, and shells are called body fossils. Most dinosaur fossils are collections of body fossils. Trace fossils are rocks that have preserved evidence of biological activity. They are not fossilized remains, just the traces of organisms. The imprint of an ancient leaf or footprint is a trace fossil. |
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Fossils tell us when and where plants and animals once existed. Some life "rode" on diverging tectonic plates, became isolated, and evolved into new species. Other life dispersed to new areas as continents reconnected, oceans narrowed, or chains of volcanic islands formed. Finding identical or similar fossils in areas separated by vast distances were some of the first clues that scientists used to reconstruct past plate movement.
Paleontology is the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old, although the fossilization process continues to occur and affect current and younger specimens. The oldest known fossils are an estimated 4 billion years old.
Paleontology is the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old, although the fossilization process continues to occur and affect current and younger specimens. The oldest known fossils are an estimated 4 billion years old.
Earth's Resources
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Natural resources are materials from the Earth that are used to support life and meet people’s needs. Any natural substance that humans use can be considered a natural resource. Oil, coal, natural gas, metals, stone and sand are natural resources. Other natural resources are air, sunlight, soil and water, as well as animals and plants.
Renewable resources are natural resources such as trees, water, sun and wind that can be replenished at about the same rate at which they are used. Renewable resources, however, can be depleted if not properly managed or conserved. Nonrenewable resources are natural resources that are depleted more quickly than they can regenerate. Fossil fuels like oil, coal and natural gas were formed over millions of years. Once mined and used completely, nonrenewable resources are gone forever. |
Watch the video to learn more about renewable and nonrenewable resources, and then download the practice GED questions:
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Natural Disasters
Structure of the Earth - Part 1
1. Read the following text from Kaplan GED.
Structure of the Earth - Part 2
1. Read the following article from Newsela.
| how_did_scientists_calculate_the_age_of_the_earth.pdf |
2. Answer the practice GED questions here.
Earth's Resources - Part 1
1. Read the following text from Kaplan GED.
| earths_resources.pdf |
2. Answer the practice GED questions here.
Earth's Resources - Part 2
1. Read the following article from Newsela.
| natural_resources.pdf |
2. Answer the following practice GED questions.
| practice_ged_questions__earths_resources_.pdf |
Climate and Weather - Part 1
1. Read the following text from Kaplan GED.
| weather_and_climate.pdf |
2. Answer the following practice GED questions.
| weather_and_climate_ged_practice_questions.pdf |
Climate and Weather - Part 2
1. Read the following article from Newsela.
| newsela-_weather_and_climate.pdf |
2. Answer the practice GED questions.
| ged_weather_and_climate_questions.pdf |
The Solar System - Part 1
1. Read the following text from Kaplan GED.
| science_-_solar_system_text.pdf |
2. Answer the practice GED questions.
| solar_system_questions.pdf |
The Solar System - Part 2
1. Watch "Introduction to the Solar System"
2. Read "Why is the Earth Rotating?" and answer the comprehension questions.
| why_is_earth_rotating_-_text_and_questions.pdf |
3. Complete the practice GED questions.
| solar_system_ged_practice_questions.pdf |
Earth Science Review
Take this GED practice test to review all you've learned this quarter:
| earth_science_review.pdf |