Performance Indicator 2.1
"Explain how the atmosphere (air), hydrosphere (water), and lithosphere (land) interact, evolve, and change."
Earth is surrounded by a thin layer of gases called the atmosphere . Earth’s atmosphere has evolved over time containing a combination of gases. Currently these gases include nitrogen (78.1%) and oxygen (20.9%) with small amounts of water vapor, carbon dioxide (.03%) and other trace gases (sulfur dioxide, hydrogen sulfide, methane and ammonia). The atmosphere is divided into distinct layers: troposphere, stratosphere, mesosphere and thermosphere. As the altitude of the atmosphere increases the air pressure deceases. Air pressure is the force of push from gas molecules. These gas molecules get weight by the pull of gravity. This weight creates a push against Earth.
The bottom layer of the atmosphere is called the troposphere . Due to the warmth from Earth the lower portion of troposphere is warmer than the upper portion of the same layer. Weather systems are created in the troposphere by convection currents . The different densities of warm and cool air produce convection currents or circulation of warm and cool air. As altitude increases the temperature decreases within the troposphere. Approximately 12km above the surface of Earth the temperature stabilizes at –60 degrees.
The stratosphere is the next layer in the atmosphere. The temperature does not vary much during the first 10km of the layer. After that the temperature can increase to a maximum of approximately 8 degrees Celsius. The ozone layer is present in this layer of the atmosphere, which is responsible for the gradual rise in the temperature. At roughly 42km the ozone layer has its main concentration, which will absorb ultraviolet radiation and generate heat.
Beyond the stratosphere lies the third layer of the atmosphere called the mesosphere . Due to the increasing distance from the warmth of Earth’s surface, the temperature in this layer starts to decrease. The higher attitudes of this layer can have temperature of –80 degrees Celsius.
The thermosphere and exosphere are the outermost layers of the atmosphere. Auroras are formed in this layer by collisions between charged particles called ions . These ions are formed in the lower portion of the thermosphere called the ionosphere . The gas particles are very far apart so solar winds can pass through this layer easily causing the gas particles to speed up. Thus causing temperatures to increase gradually as the attitude increases. Thermosphere and exosphere are the parts of the upper atmosphere of the Earth where artificial satellites and spacecrafts are revolving.
The lithosphere is the solid layer surrounding Earth. The lithosphere is covered mainly by a relatively thin layer of water called the hydrosphere . The crust and upper mantle are what compose the lithosphere. Earth’s crust, under the ocean, is approximately 7-8km thick and under the continents can be up to 70km. Below the crust lies the mantle. Two divisions make up the 2900km thick mantle.
Rocks are the building block of Earth. Minerals are inorganic substances that are naturally formed and have the same properties and composition throughout. Rocks are made up of minerals. There are only about 20 out of thousands of minerals that are universal to nearly all rocks. Minerals can be identified by different properties: color, streak, luster, density, cleavage, crystals and hardness.
Color is not a very reliable property however it is the most obvious. When a mineral is rubbed on a rough surface it will leave a power called a streak . The streak left by a mineral sample will always be the same as all samples of that exact mineral regardless for the minerals’ color. The next property of minerals is luster. Luster is the appearance of the mineral under light. If a mineral reflects light and shines like gold, silver or copper, it is said to be metallic . Pearly, dull, glassy waxy or brilliant can describe a nonmetallic luster. Density is the relationship between an objects mass (how many particles) and volume (the amount of space). Density is found by diving mass by volume. Density does not change with size; it is always a relationship between what you have and how much space it takes up. Cleavage and fracture describe how a mineral breaks. Minerals cleave when they crack along flat planes. Minerals can cleave in one, two three or more directions. Quartz will break unevenly or fracture. Minerals that have room to grow can grow crystals. Crystals form distinctive shapes. A mineral such as lodestone displays yet another property called magnetism. The hardness is measured on a scale form 1 to 10 called Mohs’ Scale of Mineral Hardness . A hard mineral such as a diamond is given a rating of 10, while a soft mineral such as talc is given a rating of 1. The other minerals fall in between.
Hardness |
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2.5 |
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3.5 |
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4.5 |
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5.5 |
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6.5 |
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Fossils are remnants of organisms that no longer exist. Fossils are found in sedimentary rock. Sedimentary rock is formed by the movement of rock fragments to a different location. Weathering rock can be carried away in little pieces by wind or water. The buildup of these pieces is called sediment. Layers on top of layers of sediment will become cemented by pressure and or evaporation of water to form sedimentary rock. Plants, animals, animal tracks or burrows can be caught in this rock and become fossilized. These fossils can tell use a lot about what used to walk, grow and live on the planet.
Weathering is the process by which rock is physically and chemically broken down into smaller pieces. Weathering creates soil, a combination of rock pieces and organic material. Rocks are exposed to the decomposing element such as air, water, plants and animal. There are four types of physical weathering: exfoliation, frost action, root pry and abrasion. Exfoliation is the flaking of the rock. Frost action has to do with the property of water when freezes it expands. As water enters cracks in rock it will expand and eventually cause the rock to break. Root pry is caused by a germinating seed growing within a crack of a rock. The roots will eventually cause pressure to form on the rock that will split the rock. Abrasion is formed by movement of rock fragments in streams, down hill or blowing in the wind. As rock pieces tumble down a hill they come in contact with each other knocking off sharp edges, making them more rounded. When a rock undergoes chemical weathering its chemical composition will change. Water will combine with certain minerals in the rock to form a new substance in a process called hydrolysis. Weathering wears away at Earth’s surface as does erosion. Erosion is the process by which the weathered material, sediment, gets transferred to another location by gravity, running water, wind and glaciers. The powerful force of erosion is gravity. Without gravity there would be no air pressure or the rushing of water downhill.
Water moves in a cycle through the atmosphere, lithosphere and hydrosphere. The water cycle starts with water changing from a liquid to a gas (water vapor) by evaporation. Water vapor is then transferred around by winds in the atmosphere. The water vapor releases heat energy and condenses forming clouds. Once the water droplets grow large they fall in the form of rain. The water is then returned to Earth’s surface. When water falls to the surface this is called Precipitation. Gravity is the force that pulls the water down to the ground. Water can also escape from planets leaves due to a process called transpiration.
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