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This video talks about mechanical and chemical weathering.
The video is: http://unitstudiesbygwen.com/video/weathering/player.html
Slide 2: Weathering is the breaking apart of rocks and minerals due to the weather.
Slide 3: The sun is a sphere and it shines evenly.However, earth’s surface doesn’t receive sunshine evenly. Some parts of the earth get more sunshine than other parts.Since the sunshine is energy, this means that different parts of the earth get more energy from the sun than other parts.
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The unequal sunshine makes different climates on earth.There are polar climates at the north and south poles. They are icy and cold all year long, and the air is very dry.Temperature climates receive more sunshine than the polar climates. Temperature climates have weather changes from cold to hot. Tropical climates get a lot of sunshine and are hot all year long.
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The tundra has long winters and almost no trees grow. The winters are long and the summers are short. The boreal forest commonly has evergreens growing in it. The winters are long and the animals that live there are used to the cold. The deciduous forests have trees that loose their leaves in the fall. These areas are temperate. Prairies, or grasslands, are found in the grasslands, which is too dry for most trees. These are also temperate areas. Desserts are dry. Some deserts are sandy. The plants and animals that live in the desert have adapted to less water. Rainforests are wet and have lots of vegetation and the big ones are in the tropical regions.
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The types of weathering that occur in the rainforests are different from the weathering that occurs in the tundra. Let’s learn about the different kinds of weathering to see which kinds of weathering are common in which places.
Slide 7
Mechanical weathering doesn’t change the property of the rocks or crystals. If the rock was granite before, it’s granite after the weathering—it’s just smaller. Chemical weathering changes the chemical composition of the rock. Chemical weathering might take out the calcium or add some hydrogen or any other combinations of stuff, but the end rock is different from the beginning rock.
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Plants can grow in the cracks of rocks. As the roots grow, they can cause the rock to split more.Animals can dig at the ground, and this causes mechanical weathering.Remember, with mechanical weathering, the rock stays the same. It’s the same rock. It was just made smaller.
Slide 10:
Soak some beans in water overnight. Mix some plaster (or dried out playdough). Put beans in the plaster and cover three quarters of the way. Label this the experiment. Make clay beans or find some rocks of a similar size to your beans. Add those to another container of plaster and label that the control. Cover both containers with a wet paper towel. Keep the paper towel moist for a week or two. Watch the plaster as the beans sprout.
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Living things can cause chemical weathering. Some plants, such as lichen, grow on rocks.
Plants can release acid that dissolves rocks.
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Air can pick up small pieces of sediment and move it to other areas. This is called deflation.When the wind blows those small pieces of sediment against rocks, this causes mechanical weathering, as the wind-blown sediment slowly pounds away at the rock. The pounding of the rock with the sediment in the air is called abrasion.
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The air we breath is about 21% oxygen.
The oxygen in the air can combine with the rock to create new minerals.
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Just like with air, water can pound against rock and cause mechanical weathering. Unlike air, water has another mechanism to cause mechanical weathering. Water can freeze. When it freezes, water expands. The water melts, more water comes, it freezes again, and expands.
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Water combines with particles in the air, like volcanic gases and industrial pollution, to make acids. Acids dissolve the rock, and can change the chemical composition of it. This sculpture of Nero has been weathered and has lost some definition.
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Chemical weathering can make physical weathering operate faster and physical weathering can make chemical weathering operate faster.Take three glasses. Put water in two of the glasses. Put candy in all three glasses. Label the glass without water “Control.” Label the next glass “only chemical weathering.” Label the third glass “chemical and physical weathering.”Take the glass labeled chemical and physical weathering and swirl it for a minute. Let all the glasses sit. Come back in twenty minutes and notice which candies have dissolved more.While the candies in the “chemical only” glass have dissolved somewhat, the candies in the physical and chemical glass have dissolved much more.
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Chemical weathering is faster when there is plenty of water. This is for two reasons. Firstly, the water combines with particles in the air to make acid. Secondly, more living things live in wet areas, and living things produce acids. Chemical weathering is also faster when it is warmer, because increased temperature speeds up chemical reactions.
Physical weathering, like water freezing in rock cracks, thawing, and re-freezing, requires cold temperatures to freeze, and it requires water to weather.
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The arctic tundra is cold and dry, so little chemical weathering occurs there. The rainforests, however, are hot and wet and chemical weathering does well there.
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Soil is composed of mineral matter, the remains of living things, water, and air. Soil is 45% mineral matter, 5% humus, about 25% water and about 25% air.
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Mineral matter is weathered rock, and it’s the biggest component of soil.
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Pedalfers have Aluminum and Iron in them, and they occur in temperate climates with moderate to high rainfall. The rainfall washes the calcium and magnesium away, so you are left with aluminum and iron. Pedalfer soils are common in forests, such as the deciduous forests of the eastern United States. These soils are good for farming.
Pedocals are soils that have calcium carbonate in them. These soils occur in dry areas. This soil is fertile, but to grow anything in it, you need irrigation.
Laterite soil occurs in warm, humid climates like rain forests.
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The O Horizon is also called the organic layer. The O Horizon has the most humus, or the remains of living things, in it. The O Horizon lies on the surface of the soil.
The A Horizon is just below the O horizon. The A horizon is also called “top soil.”
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