Weathering and Soil Formation

Explain why a single 500 kg block of granite weathers much more slowly than 100 chunks of granite weighing 5 kg each.

A rock weathers faster when more of its surface area is exposed. A big block of granite has very little surface area exposed relative to its large volume. Smaller blocks of granite have the same volume as the larger rock, but they have a much greater surface area exposed.

sod

A thick mass of grass roots and soil.

The most leaching of minerals occurs from the ____________________ horizon into the ____________________ horizon.

A, B

oxidation

Chemical weathering process that occurs when some minerals are exposed to oxygen and water over time.

How does contour farming help to reduce soil erosion?

Contour farming helps to reduce soil erosion by slowing the flow of water down fields planted on a slope.

Most plant roots grow in the ____________________ horizon.

1 (horizon A)

The ____________________ horizon in Figure 7-1 contains the most humus.

1 (horizon A)

Topsoil is the ____________________ horizon in Figure 7-1. 1 (horizon A)

1 (horizon A)

The ____________________ horizon shown in Figure 7-1 is most like the parent material.

3 (horizon C)

651-02-04-01-00_files/i0210000.jpg Figure 7-2 In Figure 7-2, which picture shows ice wedging: A, B, or C?

A

651-02-04-03-00_files/i0210000.jpg The correct labels for the numbers in Figure 7-1 are (1) ____________________, (2) ____________________, and (3) ____________________.

A horizon, B horizon, C horizon

humus

Dark-colored, decayed organic matter that supplies nutrients to plants and is found mainly in topsoil. The rich humus allowed a lush plant community to grow.

How does climate affect the rate of weathering?

Different climates affect the rates of weathering. In cold climates, the freezing and thawing that occurs causes rapid mechanical weathering through the process of ice wedging. In warmer climates, chemical weathering is more rapid because the chemical reactions that dissolve rocks and minerals are accelerated by warm temperatures.

What is differential weathering?

During differential weathering, hard rocks weather more slowly than soft rocks under the same climate conditions.

In the 1930s, an area in the southern Plains states was named the ____________________ because the topsoil turned to dust.

Dust Bowl

horizon

Each layer in a soil profile -- horizon A (top layer of soil), horizon B (middle layer), and horizon C (bottom layer). Soil is divided into different layers called horizons.

Describe the factors that influence the development and type of soil in a certain area.

Factors that determine a soil's characteristics include: the type of parent rock from which the soil forms, the climate in the area, the slope of the land, the type and amount of vegetation, and the length of time the rock has been weathering.

Describe the practice of no-till farming.

Farmers who practice no-till farming do not remove the stalks of plants after they harvest the crop. Instead, the leave the stalks in the ground over the winter. When they plant new seeds the next spring, they leave the old stalks in the soil. The stalks provide protection and cover for the soil, reducing runoff and erosion.

terracing

Farming method used to reduce erosion on steep slopes.

Why might weathering occur more rapidly in Nepal than in Kansas?

Nepal is at a much higher elevation than Kansas. Weathering occurs at a faster rate at higher elevations because there is more wind, rain, and ice at higher elevations.

chemical weathering

Occurs when chemical reactions dissolve the minerals in rocks or change them into different minerals.

Soil Formation

One of the major products of weathering is soil. Soil is a combination of particles of rocks, minerals, and organic matter produced through weathering processes. Soil contains the necessary nutrients to support various forms of plant and animal life. As a result of the weathering processes and biologic activity, soil horizons (layers) form. Soil horizons vary in depth depending on an areas climate and weathering rates.

Millions of years ago, the Appalachian Mountains were towering, craggy mountains. Describe the processes that resulted in the lower, more gentle mountains that we know today.

Over millions of years, weathering broke down the rock in to small pieces. This process included both chemical and mechanical weathering. The small pieces of rock were then carried downhill by gravity and water.

mechanical weathering

Physical processes that break rock apart without changing its chemical makeup; can be caused by ice wedging, animals, and plant roots.

contour farming

Planting along the natural contours of the land to reduce soil erosion.

Why is it important to prevent soil erosion?

Plants cannot live without soil. It is important to prevent soil erosion to ensure that plant and crops have rich topsoil in which to grow.

Explain how every living thing on land depends on soil.

Plants depend directly on soil to live and grow. Animals depend on plants to live and grow, or on other animals that depend on plants.

contour plowing

Plowing fields along the curves of a slope to prevent soil loss. Run-off is slowed in a contour plowing field.

leaching

Removal of minerals that have been dissolved in water. Leaching in soil is a major concern for farmers.

How does elevation affect the rate at which rock weathers?

Rocks at higher elevations are exposed to more rain, wind, and ice than those rocks at lower elevations. This causes the rocks to weather faster. Gravity also affects weathering at higher elevations. Steep slopes cause rainwater to quickly run off the sides of mountains, continually removing sediment and exposing new rock. The increased surface area of the new rock means an increased rate of weathering.

dust bowl

Term used to describe the central and southern Great Plains in the 1930s when the region sustained a period of drought and dust storms. During the 1930s, the usually fertile Great Plains became so dry that they were called the Dust Bowl.

Describe the practice of terracing and how it can help to reduce soil erosion.

Terracing is a type of agriculture used on steep slopes. Flat areas much like steps are cut into the slope. Crops are grown in the flat areas. This helps to reduce soil erosion by reducing runoff.

crop rotation

The planting of different crops in a field each year to maintain the soil's fertility.Landscapers can use sod to quickly establish a lawn.

The process by which softer, less weather resistant rocks wear away and leave harder, more weather resistant rocks behind.

The process by which softer, less weather resistant rocks wear away and leave harder, more weather resistant rocks behind.

differential weathering

The process by which softer, less weather resistant rocks wear away and leave harder, more weather resistant rocks behind.

What happens to the rate of chemical weathering if a rock undergoes mechanical weathering? Justify your answer.

The rate of chemical weathering will increase because the rock that has been mechanically weathered will be smaller and have more surface area.

Which do you think will weather at a faster rate, sandstone or granite? Why?

The sandstone will weather faster because it is softer than granite.

soil profile

Vertical section of soil layers, each of which is a horizon. Soil horizons are mapped out in a soil profile.

In Figure 7-2, which picture shows weathering that involves carbonic acid: A, B, or C?

c

Soils in ____ contain little organic material and are thin. a. tropical areas c. prairies b. deserts d. temperate forests

c.

Mechanical weathering is more rapid in a ____ climate.

cold

A type of plowing known as _________________________ helps conserve soil by disturbing it as little as possible.

conservation plowing

Water and wind can ____________________ soil, or carry it away.

erode

Figure 7-2 In Figure 7-2, are the animal burrows in B an example of chemical or mechanical weathering?

mechanical

Carbonation http://www.regentsprep.org.education2020.us/Regents/earthsci/units/weathering/weathering.cfm?date=MS8xNS8yMDE2IDQ6MDU6MzUgUE0%3d&u=ZjNjY2MyNmQtZWI1MS1lNTExLTgwYzYtZWNmNGJiYzM5Y2Rj&tbopt=MTExMDAwMDAwMDAw&preflang=RW5nbGlzaA%3d%3d&hash=8rIuqHPB6ZxNAjCQynI4iQ%3d%3d

occurs when carbon dioxide interacts chemically with minerals. When carbon dioxide is dissolved in water, it forms weak carbonic acid. Carbonic acid when it comes in contact with the surface of the earth dissolves large masses of limestone, creating caves and caverns. Other common terms associated with carbonation are sink holes, karst topography, stalactites and stalagmites

Weathering rates

overall depend on 3 different factors: Particle size/surface area exposed to the surface Mineral composition Climate

Name three things farmers can do to reduce soil erosion.

Answers may include: no-till farming, contour farming, terracing, planting shelter belts of trees, and grazing management.

Which type of weathering do you think is more rapid in your area? Justify your answer.

Answers will vary. In colder areas, the students should answer mechanical weathering due to freezing and thawing. In warm, wet areas, the students should chose chemical weathering because the chemical reactions occur more rapidly in warm and wet areas.

natural resource

Anything in the environment that humans use. Oil and wind are both natural resources.

climate

Average weather pattern in an area over a long period of time; can be classified by temperature, humidity, precipitation, and vegetation.

Describe how the rates of mechanical and chemical weathering might differ in the Congolese rainforest and the Siberian steppes.

Because the Congolese rainforest is hot and wet, the rates of chemical weathering will be greater there than in Siberia. However, the rates of mechanical weathering will be greater on the Siberian steppes due to freezing and thawing ice.

Describe three ways soil can be damaged or lost.

First, damage to soil occurs when it becomes exhausted, or loses its fertility. Loss of fertility can result from planting the same crop in the soil year after year. Second, soil can be damaged or lost when it is not protected from water erosion. Normally, plant roots hold the soil in place. If plants are removed from the soil, rain can easily wash the soil away. Third, wind erosion can result in the loss of dry, unprotected soil. One example of wind erosion was the Dust Bowl on the Great Plains.

Two property owners flatten the steep slope of their yards and plant more grass and shrubs. Describe two ways in which these changes will affect runoff and erosion in the yards.

First, vegetation reduces runoff by absorbing water and holding soil in place. Second, flat land has less runoff than steeply sloping land. Less runoff generally means less erosion, so the amount of erosion in each yard should be reduced.

What human activities lead to soil erosion?

Human activities include construction projects, plowing, cutting down forests, removing natural vegetation, and overgrazing sheep and cattle.

Why might farmers in Brazil who get their fields by clearing rainforest need to clear new fields after only a few years?

In tropical forests, the nutrient rich topsoil is only centimeters deep. When forests are cleared, the soil is exposed to wind and rain. The thin layer of topsoil is quickly eroded in fields cleared from rain forest. When the topsoil is gone, plants won't grow well and the farmer may be forced to clear new fields for his crops.

weathering

Mechanical or chemical surface processes that break rock into smaller and smaller pieces.

What type of weathering will occur more rapidly in an area with extremely cold winters and hot summers?

Mechanical weathering

ice wedging

Mechanical weathering process that occurs when water freezes in the cracks of rocks and expands, causing the rock to break apart.

no-till farming

Method for reducing soil erosion; plant stalks are left in the field after harvesting and the next year's crop is planted within the stalks without plowing.

soil

Mixture of weathered rock and mineral fragments, decayed organic matter, mineral fragments, water, and air that can take thousands of years to develop. Soil takes thousands of years to develop but is very susceptible to erosion.

How does soil erosion affect streams and rivers?

Severe soil erosion can clog streams and rivers with sediment.

How might small mammals cause weathering?

Small mammals cause mechanical weathering as they burrow in to the ground. This breaks up sediment and pushes it to the surface. Once on the surface, other forms of weathering can act on the sediment.

How does the surface area of a rock affect the rate at which it weathers?

Smaller rocks have a larger surface area to volume ratio than larger rocks. This means that a larger proportion of the rock is exposed to the forces of weathering. As surface area increases, so does the rate of chemical weathering.

conservation plowing

Soil conservation method in which the dead stalks from the pervious year's crop are left in the ground to hold the soil in place. In order to prevent soil erosion, the farmer used conservation plowing and left the stalks of his crop in the field.

How does soil erosion damage soil?

Soil erosion removes the nutrient-rich, water holding layer of topsoil.

How does soil form?

Soil forms when a parent material begins to weather. Over time, plants and other organisms add decaying organic material to the weathered bits of rock to form soil.

What is soil composed of?

Soil is composed of weathered rock, decayed organic material, mineral fragments, water, and air.

soil conservation

The management of soil to prevent its destruction. Terracing and no-till farming are both methods of soil conservation.

litter

Twigs, leaves, and other organic matter that help prevent erosion and hold water and may eventually be changed into humus by decomposing organisms. Litter covered the ground in the forest, providing a home for many small organisms.

How can overgrazing lead to soil erosion?

When arid land is overgrazed, sheep or cattle can strip an area of nearly all of its vegetation. If all of the vegetation is removed, there is nothing to protect the soil. Without that protection, soil can be carried away by wind and water.

In the Great Plains, ____________________ removed the grass and exposed the soil to wind erosion.

plowing

The three horizons in Figure 7-1 make up a soil ____________________.

profile

The thick mass of grass roots that helps hold prairie soil in place is called ____________________.

sod

By leaving crop roots in the ground and stalks on the surface, no-till plowing helps prevent ____________________.

soil erosion

TEACHER: Hi, my name is Miss [? Cobb, ?] and today we're going to be talking about soil erosion. Our objectives for today are to explain why soil is so important to us, we're going to evaluate the different ways that human activity can affect Earth's soil, and then, finally, we're going to describe some different ways to reduce soil erosion. So why is soil so important to us? 00:00:20 Well, topsoil, which is the very top layer of soil, is full of nutrients, mostly from decaying plants and animals. We call that nutrients humus. And it's that humus, mixed with the weathered rock, that gives the plants the nutrients they need to grow. So without that topsoil, we wouldn't have any plants. Soil erosion is the removing of that topsoil. It usually happens by wind or water. 00:00:48 And unless we work to keep that topsoil in place, our plant life is going to suffer dramatically. So some of the ways that soil can be eroded is agricultural cultivation. And that's when farmers plant over and over again and take from the land. If they don't put back into the land, then they're eventually going to take out all the nutrients. 00:01:12 And then the plants won't grow anymore. So they need to reduce that somehow. In the past, they've used fertilizers. They're coming up with new ways to do it. Another way that soil can be eroded is from forest harvesting. And that's basically when we cut down the trees and we don't put anything back. 00:01:29 When we cut down the trees, we let the soil be exposed. And any time the soil is exposed, wind and water is going to try to take it away. So whenever we cut down trees, we need to try to put back into that land. Another possibility is overgrazing. And this is when farmers let their animals eat on the grass until it's overgrazed, which means that there's very little 00:01:54 vegetation left. The best way to reduce overgrazing is to make sure that you give the animals enough land where they're not going to damage it. If they eat all of the vegetation, then again, that soil is going to be exposed and wind and water is going to carry it away. Finally, excess sediment can happen in places like strip 00:02:13 mines and large construction sites. And that's basically where we're taking all of the soil and moving it to a different location. And when we do that, there can be a buildup of excess sediment that will end up in rivers and streams, which can cause a lot of damage. So we need to make sure that we're putting this excess sediment in a good spot, or we're putting it back onto the 00:02:37 construction site when we're done, and putting things like trees and plants in. So there's different ways we can prevent soil erosion. The first one is managing crops better. Like I mentioned before, farmers have realized that if they keep taking from the land, they're eventually not going to have any nutrients left and the plants won't grow. 00:02:56 So they started adding fertilizer to it, and that helped a little bit. Recently, we've discovered a process called no-till farming. And that's basically where-- farmers used to plow up the land every year and then replant their crops. Well, they've discovered that if they don't plow the land 00:03:11 every year, and they just plant over the dead vegetation, that gives a nice protective layer over the soil and helps the soil from being eroded away. So that's a big help. There's another way that we can reduce erosion on slopes. One of the ways is called contour farming. And that's basically when there's a nice, gentle slope. They'll make patterns with their crops. 00:03:34 And that way, it will reduce the runoff of water carrying the soil with it. It'll slow it down. So that helps prevent the soil erosion that way. If the slope is very steep, then they can do something called "terracing." Terracing, like in the picture shown here, is where on a very steep slope they plant rows of any kind of plant to help the water from carrying away that 00:04:01 excess soil. And that keeps the soil in place, and the plants can still grow. Finally, we need to reduce erosion from exposed soil. And that's just basically any time there's open, plain soil, we need to try to keep that soil there. Oftentimes, you can see this process taking place on construction sites. 00:04:19 If you've ever seen them spray down with water over the land, they're trying to reduce the soil erosion. Basically, they don't want the wind to take all of the soil away. So they spray it down with water and make it a little bit heavier. And that helps out a lot. So just to review our objectives, we explained why 00:04:36 soil is important. Remember that topsoil, which is the top layer of the land, that's where all the nutrients is, nutrients from humus, which is decaying plants and animals. And that's what gets our plants to grow-- that's where the plants get all the nutrients from. We talked about the different ways that human activity can affect Earth's soils-- 00:04:57 things like overgrazing, forest harvesting, things like that where we can actually destroy the soil that's already there. And then we described the different ways to reduce soil erosion, things like no-till farming, contour farming, and terracing-- ways that we can keep the soil that's there to stay there.

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TEACHER: Hi. My name is Miss Cobb, and today we're going to be talking about soil conservation. Our objectives for today are to explain why soil is such a valuable resource to us, we're going to list the different ways that soil can lose its value, and finally, we're going to identify the different ways that soil can be conserved. 00:00:19 So first of all, why is soil so important to us? Well, it is one of our greatest natural resources. Basically, all of our soil is what gives our plants the nutrients they need to survive. Without plants, humans could not live because of the animals and so forth that need it to grow. There's also something called sod. Sod is where there's thick, lush growth of plants, and the 00:00:46 roots become so entangled that they protect the soil. So sod is always a good thing to keep the soil in place. Some of the different ways that soil can be damaged or lost would be loss of fertility. When this happens, it's basically when farmers are growing something on the land and taking it without replacing anything back to the land. Eventually, the soil is going to lose all of its nutrients, 00:01:11 and nothing will be able to grow there. Another way that soil can be lost is through loss of topsoil. Topsoil is the shallow top land that's full of nutrients and decaying organic materials that make it so good for the other plants to grow on. If the soil is exposed, meaning that there's nothing growing on it currently, then water or wind can take that 00:01:38 topsoil and remove it. If the topsoil is lost, then nothing new will grow there. In the late 1800s, farmers were beginning to settle throughout the Great Plains, the middle section of our country. They began to farm the land and over time, they didn't realize that the more they took from the land, the less they were going to be able to get from it. 00:02:03 There were large droughts happening, which is a reduction in the rainfall. And beginning of the 1900s, they started having severe droughts over and over again. When that happened, because they were farming the land so much, the wind started just taking the topsoil away. And it actually blew away so much that we call that section of the country "the Dust Bowl," because we've lost so 00:02:31 much topsoil that they couldn't get anything to grow. And the dust actually blew for miles and miles all around the country. There are different ways that we can conserve soil, though. The first one is called contour plowing. And that's when farmers-- anytime there's a slope, they make patterns in their farming. 00:02:51 The reason why they do that is when the rainfall comes and it flows off the land, it's going to be slowed down. And slower water takes less of the soil with it. So any time that they can make patterns like that, it's going to slow the erosion of the topsoil. Another thing's called conservation plowing. And this is basically where farmers used to till up, or plow up, their land every year before they would plant 00:03:16 something new. In recent times, they've discovered that the less plowing they do, the more nutrients is left in the ground. So what they'll do is, instead of plowing, they'll just let the dead material lay and plant right over it. That way, they're not pulling all that nutrients right out of the ground. 00:03:32 And finally, they do something called crop rotation. Different plants pull different nutrients from the ground. Things like corn, for example, pull a great amount of nutrients from the ground. So when farmers plant things like corn, the next year they'll plant something that takes a lot less from the ground, and can actually return it. 00:03:51 That way, if they rotate what crops they grow, they're actually not taking nearly as much from the soil. So just to review our objectives, we explain why soil is such a valuable resource. Remember that all plants need soil to grow, and without plants, we could not survive. We talked about the different ways that soil can lose its value, such as loss of fertility, where we take all 00:04:12 the nutrients out of the ground, and loss of topsoil, where wind or rain take away the topsoil so no plants can grow. And we talked about different ways that soil can be conserved, things like contour plowing, where they make patterns in the slope. That way, the wind and water won't take it away nearly as quickly. 00:04:31 And crop rotation, where they plant one crop one year and another a different year to help conserve those nutrients in the ground.

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TEACHER: Today we're going to be talking about rates or speed of weathering, or breaking down. So we're going to look at how fast rocks break down in different situations. We're going to be looking at porosity, or how porous or open a rock is, or a substance is, to allow water to seep through it. So we're going to explain how the composition of rock 00:00:21 affects the actual rate of weathering. In order to illustrate this, today we will be using a gizmo. In today's gizmo, we're going to be looking at three different substances. We have gravel, sand, and silt. First of all, we need to understand porosity. Porosity is something that can be measured by looking at the 00:00:42 amount of substance or amount of liquid that goes through a substance divided by how much liquid we have. It's a ratio of these two things. So what does this have to do with rate of weathering? Well, permeability, or the amount of water that can seep through a substance because of the amount of space between the particles, is directly related to affecting weathering. 00:01:07 Weathering has two main factors that affect it. One of them is the type of rock. All different rocks are arranged differently, their particles are arranged differently, which is what we're looking at today. The type of rock. The other one is the climate. If it's hot and there's a lot of water around to allow it to 00:01:24 break apart or have chemical reactions, then that's the other one that will allow rocks to weather. So the climate or the weather, as well as the type of rock, depending on the porosity or permeability. So let's go ahead and look here at today's example of different types. We're going to have gravel, sand, and silt. So we're going to do is, we're going to open up this water. 00:01:51 And what we have on the bottom, first of all, you need to know that each one of these, gravel, sand, and silt experiments, we have 300 milliliters of the substance, of the solid, and now we're going to pour water on top of them. Let's open up the sand and see what happens. Let's go ahead and turn it on. And watch what happens. 00:02:10 OK, I'm going to pause it. You can see that some water is going to get caught on top and then it's going to seep through. But there is some water being held out on top, right? So you can see that the surface water is there, but then it goes ahead and is mixed. Let's go ahead and look at gravel. Let's see how hard it is for water to seep through gravel. 00:02:36 OK, it doesn't really look like its seeping through with any difficulty, just goes right to the bottom, right? And then let's look at silt. So it's going to go through and it actually is going to get caught on the surface. Some is going to seep through, but the porosity is going to be much less than the others, OK. So let's turn this off. 00:02:58 And you can see that there's actually standing water on top of the silt and yes, some water is seeping through, and it's happening quite slowly. What does this have to do with what we're talking about? Well, it has to do with permeability. We say that gravel is more permeable because it has more openings. Now let's look at a macroscopic view. 00:03:19 And you can see that the gravel has these chunks and there are big air pockets. That's what the white is. There are spaces in between where the water can flow. If we were looking at sand, you can see that the sand particles are smaller and they're more closely together and there are not as many white air pockets. But there is some for the water to seep through. 00:03:43 Then when we look at the silt, you can see that it's more clumped together and there are also spaces as well, but they are much smaller. All right, so those are just different ideas on understanding that there is a permeability and that has water going through it. Once the water goes through a rock, it can break it up into different pieces. 00:04:06 And that is what weathering is. Weathering is water going through and breaking up rocks, as well as having high temperatures and having water in the environment. That's the climate, but also the type of rock. All rocks are a little bit different.

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eNotes Glossary Transcript Section 1 00:00:00 TEACHER: Hi. My name is Miss [? Cobb, ?] and today we're going to be talking about weathering. Our objectives for today are to explain how mechanical and chemical weathering are different. We're going to describe the different weathering effects on Earth's surface. And then we're going to explain how climate can affect 00:00:14 the rate of weathering. So first of all, what is weathering? Well, weathering is any process that weakens and breaks down the rocks. There are two major kinds of weathering. There's mechanical weathering and chemical weathering. Mechanical weathering is any time there's an actual physical thing that is breaking down the rocks. 00:00:31 Some of the things included in that are plants and animals. As plants grow their roots inside rocks they break it apart, and that's mechanical weathering. Animals also like to build their homes in rocks. So as they dig and move the rock around, they're breaking down the rock around them. Ice wedging is another mechanical weathering. That's when water seeps into the rock, and then when it 00:00:52 freezes, it expands and can break apart and crack open rock. One of the major things that affects mechanical weathering is surface area. Surface area is how much of that rock is actually exposed for it to be broken down. The more surface area a rock has, the faster it's going to be broken down. 00:01:10 Interesting fact with that is artists will actually, when they build a sculpture and they know it's going to be outside and it will get weathered, they'll polish it. And they don't do this for how it looks, but they actually do this to create less surface area, and that way it will get weathered a lot slower. There's also chemical weathering. And chemical weathering is anytime the natural acids can 00:01:33 break down the rock. This can occur from the natural acids in water or air. And it can also occur from the natural acid that plants produce. So it basically is a chemical process the breaks down the rock. Another chemical process is what we call oxidation. And that's when the oxygen in the air mixes with the water 00:01:53 in the air, and it breaks down the rock very quickly. A good example of this would be the Statue of Liberty. It's actually made of bronze, which should be like a penny-like color. But, because of the oxygen in the air and the water in the air, it is oxidized, turning it into a green color. So that's chemical weathering. There are different things that affect the rates of how 00:02:14 quickly things get weathered. One of the major causes is climate. Climate is how cold or hot it is, and it's also how much moisture is in the air. The greater the extreme in cold and hot, the faster the weathering is going to happen. This usually occurs because of the water freezing. And if it freezes it, it's going to break down the rock 00:02:33 even faster. Also, if the moisture is in the air, then oxidation is going to happen more easily. Another thing that affects the rate of weathering is the rock type. If a rock is very, very dense and hard, it's going to weather more slowly than a rock that is less dense and softer and can be worn away more easily. 00:02:52 So just to review our objectives, we explained the difference between mechanical and chemical weathering. Remember that mechanical weathering is an actual physical thing that's wearing away the rock, while chemical weathering is acid wearing away the rock. We described the different weathering effects on Earth's surface. Anytime there's surface area exposed, the rock 00:03:13 can get worn away. And we explained how climate can affect the rate of weathering. Remember, the greater difference in cold and hot and the more moisture in the air, that's going to speed up the rate of weathering.

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s Glossary Transcript Section 1 00:00:01 TEACHER: Hi, my name is Miss Cobb, and we're going to be talking about the rates of weathering. Our objectives for today are to explain how the composition of rock can affect the rate of weathering. We're going to describe how a rock's total surface area can increase the rate of weathering. And finally, we're going to describe how differences in elevation and climate can affect the rate of weathering. 00:00:21 So first we're going to talk about differential weathering. And this is, basically, that softer rock is going to weather faster and harder rock, which is going to weather slower. And because the earth's crust is made of many different types of rock, you're going to see differential weathering, meaning that the soft rock is going to be worn away, while the harder rock is going to remain. 00:00:39 So that's how we get such interesting land features on our earth. Like the picture that's shown there, the softer rock around the base was worn away and the harder rock was left. So we can get all sorts of neat shapes that come out of the earth's surface. The shape of rocks also affects how quickly they weather. 00:00:57 The more surface area available to be worn away, the faster it's going to weather. So if you have the same amount of rock and one solid rock, that's going to weather slower than if you have the same amount with lots of little tiny rocks, it has more surface area, so it's going to weather quicker. The more surface area exposed, the faster it's going to be worn away. 00:01:19 Weather and climate also affect the rate of weathering greatly, too. Temperature is a big factor. The more extreme temperature there is, that means the difference between cold and hot, the faster it's going to weather. Also water is a big factor in the rate of weathering. The greater the water content, the faster 00:01:37 it's going to weather. And this doesn't have to be water wearing over the rock, which can create weathering, but it's also the water in the air. Water can be great accelerant of weathering, too, because if it freezes, it's going to crack open the rock. And that's a type of mechanical weathering. So the greater the water, the faster the weathering. 00:01:59 Elevation is also a huge factor in weathering. The higher the elevation, you're going to get more rain, water, ice, and wind. And all of those can lead to mechanical weathering, so the higher the elevation, the faster the weathering will happen. So just to review our objectives, we talked about how the composition of rock can affect the rate of 00:02:20 weathering. Remember, the harder the rock, the slower it's going to weather. The softer the rock, the quicker it's going to weather. We described how a rock's total surface area can affect the rate of weathering. The more surface area exposed, the faster it's going to be worn away. 00:02:34 And we described the difference in elevation and climate, how they can affect the rate of weathering. Remember, the greater the temperature extremes, the faster and there's going to be weathering. The more water that's available, the faster it's going to weather. And the higher the elevation, the faster it's going to weather.

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Chemical weathering is most rapid in areas that are

warm and wet.