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Middle School Science
Room 212 – Miss Lida
Chapter 3/Engage – Page 86
“Interactions of Earth Systems”
The Water Cycle
 The water cycle is the continuous movement of water on, above, and below Earth’s
surface.
 The Sun provides the energy that drives the water cycle and moves water from place to
place. As this occurs, liquid water can change state to a gas or a solid and then back
again to a liquid.
 The change of state requires either an input or output of thermal energy.
 Because the water cycle is continuous, there is no beginning or end.
Evaporation
 Evaporation is the process by which a liquid, such as water, changes into a gas (water
vapor).
 Water vapor, like other gases in the atmosphere, is invisible.
Transpiration and Respiration
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The oceans hold most of Earth’s water so they are a major source of water vapor. But
water also evaporates from rivers, lakes, puddles, and even soil. These sources, along
with oceans, account for 90 percent of the water that enters the atmosphere. Most of
the remaining 10 percent is produced by transpiration.
Transpiration is the process by which plants release water vapor through their leaves.
Some water vapor also comes from organisms through cellular respiration.
Condensation
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Condensation is the process by which a gas changes to a liquid.
Tiny droplets of liquid water join to form larger drops.
When millions of water droplets come together, a cloud forms.
Eventually drops of water in the clouds become so large and heavy that they fall to
Earth’s surface.
Precipitation
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Precipitation is moisture that falls from clouds to the Earth’s surface.
Rain and snow are forms of precipitation.
More than 75 percent of precipitation falls into the ocean, and the rest falls onto land.
Some of the water evaporates and goes back into the atmosphere. Some flows into
lakes or rivers, and the rest seeps into soil and rocks.
In the water cycle, water continually moves between the hydrosphere, the atmosphere,
the biosphere, and the geosphere.
Changes in the Atmosphere
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Weather is the state of the atmosphere at a certain time and place.
Scientists use several factors to describe weather:
Air Temperature – the average amount of energy produced by the motion of air
molecules.
Air Pressure – the force extended by air molecules in all directions.
Wind – the movement of air caused by differences in air pressure.
Humidity – the amount of water vapor in a given volume of air.
*Interactions – Weather is influenced by conditions in the atmosphere, the geosphere, and the
hydrosphere.
Climate
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Climate is the average weather pattern for a region over a long period of time.
Climates differ in part because of interactions between the atmosphere and other Earth
systems.
Mountains
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The climate near the top of a mountain often is cooler than the climate near the
mountain’s base.
Mountains can also affect the amount of precipitation an area receives --- a
phenomenon known as the rain-shadow effect. (where one side of a mountain has a
wet climate, while the other side of the mountain has a dry climate)
Ocean Currents
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As wind blows over an ocean, it creates surface currents in the water. These currents
transport thermal energy in water from place to place.
The Rock Cycle
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The rock cycle is the series of processes that transport and continually change rocks into
different forms.
As rocks move through the rock cycle, they might become igneous rocks, sedimentary
rocks, or metamorphic rocks.
They might take the form of sediments or hot, flowing magma.
Like the water cycle, the rock cycle has no beginning or end.
Cooling and Crystallization
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When magma flows out onto Earth’s surface, it is called lava.
Mineral crystals form as magma cools below the surface or as lava cools on the surface.
This crystallization changes the molten material into igneous rock.
Uplift
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Uplift is the process that moves large bodies of Earth materials to higher elevations.
Uplift is often associated with mountain building.
Weathering and Erosion
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Rocks on Earth’s surface are exposed to the atmosphere, the hydrosphere, and the
biosphere.
Glaciers, wind, and rain, along with activities of some organisms, break rocks into
sediment. This process is called “weathering”.
Weathering of rocks into sediments is often accompanied by erosion. Erosion occurs
when the sediments are carried by agents of erosion --- water, wind, or glaciers --- to
new locations.
Deposition
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Deposition is the formation of layers of sediment.
Over time, more and more layers are deposited.
Compaction and Cementation
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As more layers of sediment are deposited, their weight pushes down on underlying
layers. The deeper layers are compacted.
Minerals dissolved in surrounding water crystallize between grains of sediment and
cement the sediments together.
Compaction and Cementation produce sedimentary rocks.
High Temperatures and Pressure
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Metamorphic rocks form when rocks are subjected to high temperatures and pressure.
This usually occurs far beneath Earth’s surface.
Igneous, sedimentary, and even metamorphic rocks can become new metamorphic
rocks.
Uplift can bring the rocks to the surface.
On the surface the rocks are broken down and continue moving through the rock cycle.