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Chapter 6: Processes Shaping Planet Earth
Transcript of Chapter 6: Processes Shaping Planet Earth
Earths crust forms a thick skin around the Earth, much like a crust of a loaf of bread. Below the crust is the Earth's mantle.
: a region of hot, dense rock. The top of the mantle is solid.
As one travels deeper towards the earth's center, temperatures rise.
About 100km below Earth's surface, the rock is near its melting point and becomes semi-solid or plastic.
Scientists are investigating how to use Earth's heat as a source of usable, clean, geothermal energy.
The lithosphere consists of:
- the Earth's crust
- top section of solid mantle
This brittle, uppermost shell of Earth is broken into a number of tectonic plates.
What forces have helped shape Earth's landforms, climate and plant life?
PLATE TECTONIC MOTION
If you look at the map of the world, you may notice that different continents seem to fit together like a giant puzzle. For example: eastern South America seems to fill the space below West Africa. Mountain ranges that end at one coastline seem to continue again on another coastline.
Many scientists believe that several or even all of the present continents of the world once fit together into a single, giant continent. Gradually, this large land mass separated and its pieces drifted apart into their present locations.
Plate Tectonic Theory
Plate Tectonic Theory
: theory that all of the continents used to be one single continent.
The Earth's lithosphere is divided into large slabs of rock known as
Earth's continents are attached to these plates. Scientists believe these plates move as solid chunks floating on top of the more "plastic" part of the mantle.
Plates move only a few centimeters per year.
What Causes Plate Movement?
: the spread of heat through the movement of a fluid substance.
Inside the mantle, semi-solid rock is heated. As it is heated, it expands and becomes less dense (solid). This lighter rock rises as gravity pulls down cooler, denser rock in its place. After the hotter rock rises, it begins to cool down. Once cooled, it sinks, creating a circular motion or current. This circular motion pushes the plates above.
Convection inside the Mantle
- semi-solid rock is heated
- expands as it's heated and becomes less dense
- lighter rock rises & denser rock falls
-creates circular motion
- moves plates
Gravity also contributes to plate movement.
When oceanic and land plates collide, gravity pulls the dense (heavier) oceanic plate under the lighter plate.
When one end sinks, it pulls the rest of the plate with it.
EFFECTS OF PLATE TECTONIC MOVEMENT
When continental plates slowly push into one another, they often fold upwards, creating mountain chains.
Example: The Indian plate pushes northward against the Eurasian plate, they fold, creating the Himalayan Mountains.
Seafloor Spreading and Rift Valleys
Some tectonic plates move apart.
Scientists have discovered that in the middle of the
Atlantic Ocean, the separation of plates is actually causing the seafloor to spread.
As the plates move apart,
magma rises up through the cracks in the ocean floor creating a ridge of mountains.
In other areas, the separation creates rift valleys: long valleys between parallel ridges of mountains.
This creation of new crust
would increase Earth's size, except that it is balanced by the folding and colliding plates elsewhere.
EARTHQUAKES AND TSUNAMIS
Plate movements can cause a break in the Earth's crust, known as a fault.
Plate movements can also cause vibrations known as earthquakes.
As plates move, they create tremendous stress at plate boundaries.
Eventually parts of the rocky crust will break, creating a fault and sending vibrations known was seismic waves.
Scientists measure the waves sent by an earthquake with a seismograph.
They can see that most waves originate at plate boundaries. When an earthquake occurs under or near an ocean, it creates immense ocean waves of destructive force known as tsunamis.
In places where tectonic plates diverge on where one plate divides under another, pressure in the Earth's mantle is reduced and some of the hot, solid rock turns to liquid. Any part of the tectonic plate that sinks into the mantle may also melt.
Pockets of molten rock form beneath Earth's surface. This magma may break through weakness in Earth's crust. Magma, ashes and gases erupt and form a volcano.
Once the magma reaches Earth's surface, it becomes known as lava.
The location of most volcanoes and earthquakes has been shown to be almost identical with the location of plate boundaries.
the "Ring of Fire" around the Pacific Ocean - a zone of volcanoes and frequent earthquakes - coincide with the boundaries of the Pacific tectonic plates.
Many mountains and even islands have been formed by volcanoes. The
Hawaiian islands are actually the tops of volcanoes in the Pacific Ocean.
Other Forces Affecting
the wearing down of rocks at the Earth's surface by the actions of wind, water, ice and living things.
For Example: when water freezes, it expands. Water may seep into pores or cracks, freeze and then expand these pores or cracks.
Acids, chemicals and microscopic organisms can also cause rocks to break down and disintegrate.
Erosion: the process by which rock, sand and soil are broken down and carried away.
For Example: a river can cut through solid rock (creating the Grand Canyon). An ice glacier can carve a region, creating the Great lakes.
The same forces that erode one place can deposit particles and sediment in another place.
For example: rivers carry sediment downstream and deposit the sediment where they meet the ocean. The action of ocean waves can bring sand to a beach.
SOIL BUILDING PROCESS
Weathering breaks down rocks on Earth's surface. The material left behind from rocks mixes with decaying plants and animals, making soil.
Soil: a mixture of several materials including sand, clay, rock, water, fungi, bacteria and decayed plants and animals.
A layer of soil covers much of Earth's surface.
There are many different types of soils based on different mixtures of their basic ingredients.
Each type of soil has its own texture, ability to hold water & ability to support plant life.
For Example: clay and dead plant and animal material can hold water. Soils with large amounts of clay and decayed material will therefore hold more water than sandy soils.
The type of soil found in an area greatly affects the types of plants life than can grow there.
For Example: the sands of the Sahara and Arabian Deserts will not support many forms of plant life. Soils in the South American rainforests have little minerals and their plants get their minerals from decaying plants and animals. Soils found in grassland areas (The Great Plains/Pampas) have the great amounts of organic matter and are the best soils.
TYPES OF LANDFORMS
Get your types of landforms map and begin labeling the landforms on your map.
HYDROSPHERE: EARTH'S OCEANS
- More than 70% of the Earth's surface is covered in water. This is the hydrosphere.
- 97% of this water is ocean
- Most of the rest is frozen in polar ice caps
- Less than 1% is found in the atmosphere, groundwater or freshwater lakes/rivers.
THE WATER CYCLE
-Solar energy heats the Earth's surface of oceans, lakes and seas.
- This causes evaporation into the atmosphere
- Water vapor rises until it cools
- Vapor condenses into tiny droplets (clouds)
- Droplets become larger and heavier until they fall back to Earth as precipitation
Each day, the Earth's ocean levels rise and fall during high and low tide.
- Caused by the gravitational pull of the moon.
- Tides are the highest when the sun and moon are lined up on the same side of the Earth & lowest when they are on opposite sides.
-The movement of the ocean's waters.
- Occur above and below the surface.
- Surface currents are caused by the spinning of the Earth & wind.
- Under the surface, water is in different layers. Colder, salty water sinks and gradually moves towards the equator. As it does this, it pushes warm water away. This slow, but steady circulation can take hundreds of years.
THE ATMOSPHERE AND CLIMATE
Around the Earth is an envelope of gases known as the atmosphere. Contains mostly nitrogen (78%) and oxygen (21%).
Weather: refers to the conditions in the atmosphere closest to Earth.
Different processes in the atmosphere lead to different climates: the average weather conditions in an area over time.
The Geography of Weather
The Geography of Weather
Weather is affected by latitude, elevation, wind patterns, ocean currents and mountain barriers.
For Example: temperatures at higher elevations (further away from the equator) have cooler temps. Geographers call this vertical climates.
As the Earth revolves around the sun, it tilts on an axis. The direction the Earth leans towards or away from the sun determines an areas season.
Seasonal differences are greatest at the poles & least at the equator.
Distribution of Climate Regions
- High Latitude Climate: The N & S Pole have similar "polar climates" with very cold winter temps.
- Mid-Latitude Climate: Warm summers & cool winters
- Low-Latitude Climate: "tropical moist climates" such as in Central America... BUT can also be warm and dry climates such as in the Middle East.
-Temperate Deciduous Forest: mid-latitude where there is ample rain and moderate temps with cool winters.
-Tropical Rainforests: near the equator (low-latitude).
-Grasslands/Savannas/Steppes: climate is drier, not enough rainfall to support trees. (mid latitude)
-Deserts: Little or no rainfall (low latitude)
-Tundra: polar temperatures (high latitude)