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00:00Soil is the loose material that covers the earth's surface.
00:15In most parts of the world, land is covered by soil.
00:23You can think of soil as the living skin of the earth.
00:27It gives plants the nutrients they need to grow, and plants give people and animals food
00:35to live.
00:38Soil also provides building materials, homes for animals, and things we use every day.
00:48Soil is not just dirt.
00:50It is an important natural resource that provides the foundation for life on earth.
01:09Soil is made of rocks, decayed plants and animals, air, and water.
01:16Let's first look at rocks.
01:19Through a process called weathering, big rocks break down into smaller and smaller pieces,
01:25eventually becoming part of soil.
01:30Soil does not form in a day.
01:32It can take hundreds of years.
01:35Wind, water, and extreme hot and cold temperatures cause rocks to break down over time.
01:46The pieces of rock are transported from one place to another through erosion.
01:53But wait!
01:55Soil is not just tiny rocks.
01:58It is also made up of decayed plants and animals called humus.
02:04Humus is made from things that were once alive, like leaves that fall from a tree.
02:11The dead leaves decay or break down and become part of the soil, giving it nutrients.
02:20Humus is a dark color and is found on the ground's surface.
02:26There are three layers of soil.
02:29The topsoil is the top layer where plants grow, and it is only a few inches thick.
02:36Humus is part of the topsoil.
02:40The middle layer is the subsoil, and it is a combination of soil and rocks.
02:49Bedrock is the bottom layer that is made up of many layers of rock.
03:09How soil looks and feels tells us about its properties.
03:14Is it good for growing plants?
03:17How much air and water does it hold?
03:20To answer these questions, let's start with soil types.
03:24There are three types of soil – sand, silt, and clay.
03:32Soil comes from tiny pieces of weathered rock.
03:37The difference between soil types is the size of the rock particles.
03:43Sand has the largest particles.
03:45It feels rough and gritty.
03:49Sandy soil has air spaces between the grains of sand.
03:53The air space lets water drain through sand quickly.
03:57A sandcastle washes away in the tide because sand does not hold on to a lot of water.
04:07Silt has medium-sized particles.
04:10It feels smooth when wet.
04:14Silt particles hold on to more water than sand.
04:18A bird's footprint sticks to silty soil because silt does not drain as much water.
04:26Clay has the smallest particles.
04:29It feels sticky when wet and hard when dry.
04:33The small rock particles pack tightly together, holding the most water, but there is little
04:38space for air.
04:42The water helps clay keep its shape so it is used to make pottery.
04:49What is the best type of soil for growing plants?
04:54Sand does not hold enough water for most plants to grow.
04:58Clay holds water but does not contain the air that plants need.
05:03The best soil for growing plants is called loam, and it is a mixture of sand, silt, clay,
05:11and humus.
05:14Humus is made of decaying plants and animals.
05:17It adds nutrients to soil and gives it a darker color.
05:21The combination of soil and humus makes loam the best soil for growing plants because it
05:26has the perfect amount of air, water, and nutrients.
05:46Plants get the food and water they need to grow from soil.
05:51Plants absorb food called nutrients from their roots.
05:54Besides providing food and water, soil helps plants stand tall by holding their roots in
06:00place.
06:03When roots take hold in the ground, they keep soil from washing away.
06:09For example, tree roots prevent soil erosion by reaching deep and holding soil together.
06:19Farmers want to plant their crops in the best soil with the most nutrients.
06:24To prepare soil for planting seeds, a farmer uses a tractor to till the soil.
06:32Tilling mixes up the topsoil so the nutrients are near the surface.
06:39Crops grow in different types of soil.
06:42Rice grows in soil with clay that holds a lot of water.
06:48Cereal grows in sandy soil, and carrots grow best in a mixture of soils.
06:56Topsoil where plants grow is a precious natural resource because it takes a long time for
07:02rocks to become soil.
07:06Farmers try to conserve the topsoil by rotating the kinds of crops they plant and by controlling
07:12irrigation so soil doesn't wash away.
07:17When crops are harvested, the farmer lets the plants left behind decay and become part
07:23of the soil again, giving back nutrients.
07:41Worms spend their lives eating soil.
07:45They feed on decaying plants and leaves within the soil, and this behavior helps make soil
07:50healthy.
07:51Let's look at an earthworm under a microscope.
07:56A worm does not have eyes, legs, or teeth, but it does have strong mouth muscles to swallow
08:02tiny bits of soil.
08:06Worms move forward and back, eating what's in front of them.
08:14The soil passes through the worm's digestive system and comes out the other end as waste
08:19called castings.
08:22These are worm castings, and they are rich in nutrients for plants.
08:29Worms help soil in other ways.
08:32After it rains, worms crawl deep underground, creating tunnels.
08:39Deep tunnels are important because they mix up the soil, allowing air and water to get
08:44inside to help plants grow.
08:49Since worms are so helpful, farmers raise worms just like other animals.
08:55This is a worm farm, where millions of wriggling earthworms are raised and then sold to other
09:00farmers to keep their soil healthy.
09:18People and animals rely on soil to grow plants for food, but soil has other uses as well.
09:27This animal is a mole.
09:30Animals live underground, digging tunnels to look for worms and insects in the soil.
09:39Many animals, such as the kit fox, the burrowing owl, and the tiger salamander, live in burrows
09:46beneath the ground.
09:50Around the world, there are people who make their homes out of soil.
09:55Wet soil, made of sand and clay, is poured into rectangular molds.
10:02The mud bricks, also known as adobe bricks, are stacked on top of each other to create
10:07the walls of a building.
10:13Here are examples of buildings made of soil bricks.
10:25Clay soil can be used to make pottery.
10:29A lump of clay is molded by hand into cups, bowls, and vases.
10:39People in some cultures use the natural colors in soil to paint their faces and bodies.
10:46This allows people to express themselves and the traditions of their community.
10:54Soil is also used in medicine.
10:56A bacteria naturally found in soil is used to make antibiotics that treat infections.
11:16Soil is not just dirt.
11:19It is an important natural resource that provides the foundation for life on earth.
11:26Soil is made of rocks, decayed plants and animals, air, and water.
11:34Soil comes from weathered rock that is broken down and moved through erosion.
11:40There are three levels of soil, topsoil, subsoil, and bedrock.
11:46Humus gives soil nutrients and is part of the topsoil.
11:51Soil looks and feels different depending on its properties.
11:56There are three types of soil, sand, silt, and clay.
12:02Sand has the largest rock particles and feels gritty.
12:06Silt has medium-sized particles and feels smooth.
12:10Clay has the smallest particles and feels sticky.
12:15Soil is a mixture of sand, silt, clay, and humus and is the best soil for growing plants.
12:24Farmers grow plants in topsoil.
12:28Soil holds roots in place and roots help with soil erosion.
12:33Worms make nutrient-rich castings.
12:36They also create tunnels that allow air and water to reach below the surface.
12:43Soil is used in many ways, including making homes for animals and people.