What is Soil (and Why is it Important)?: Crash Course Geography #17

Summary

The Aral Sea's tragic shrinkage due to Soviet-era agricultural practices serves as a cautionary tale about soil mismanagement. The script explains soil composition, emphasizing its vital role in ecosystems. It outlines soil horizons, from the organic-rich O and A horizons to the less active C and R horizons. The importance of soil in agriculture and the current crisis of soil loss are highlighted, urging the need for soil conservation and respect for Indigenous land rights.

Takeaways

• 🌍 The Aral Sea was once one of the four largest lakes in the world, covering 68,000 square kilometers.
• 🌾 Before 1960, the region around the Aral Sea was fertile, but the Soviet-era shift to cotton and rice farming led to the overuse of water from the Amu Darya and Syr Darya rivers.
• 💧 The reduction in water inflow to the Aral Sea caused it to shrink, leading to increased salinity and the creation of a salty crust on the exposed soil.
• 🌱 The salinization of the soil negatively impacted plant growth, creating a vicious cycle where the sea was being destroyed to grow crops, but the crops couldn't grow due to the salinity.
• 🌪️ The shrinking of the Aral Sea led to the exposure of sediment, which, combined with pollutants, created massive dust storms that affected agriculture in the region.
• 🏜️ The environmental disaster at the Aral Sea is considered one of the worst of the 20th century, illustrating the importance of managing land and resources wisely.
• 🍰 Soil composition is complex and dynamic, much like the ingredients in a cake, requiring a balance of minerals, organic material, air, and water.
• 🌱 The organic material in soil, or humus, is derived from living things and plays a crucial role in supplying energy, nutrients, and influencing soil properties.
• 🌿 Soil profiles consist of layers called soil horizons, each with distinct properties that support different types of biodiversity and plant growth.
• 🌱 Soil is vital for life on Earth, supporting ecosystems and agriculture, and its health is maintained through a delicate balance of natural processes and human management.

Q & A

What was the Aral Sea's status before 1960?

Before 1960, the Aral Sea was one of the four largest lakes in the world, covering an area of 68,000 square kilometers.

Which rivers supplied water to the Aral Sea?

The Aral Sea was supplied by the waters of the Amu Darya and Syr Darya rivers.

How did the Soviet-era agricultural practices impact the Aral Sea?

During the Soviet era, the region was dominated by cotton and rice fields, which consumed most of the water from the rivers and their tributaries, leading to the sea's shrinkage.

What is the process of salinization and how did it affect the soil near the Aral Sea?

Salinization is the process where, as water evaporates, it leaves behind dissolved salts, creating a salty crust on the soil. This crust blocks plants from absorbing water and nutrients, leading to reduced agricultural productivity.

What environmental consequences did the shrinking of the Aral Sea have on the surrounding area?

The shrinking of the Aral Sea led to the exposure of sediment, which, combined with salt, dirt, fertilizers, and pesticides, created massive dust storms that endangered crops over thousands of square kilometers.

Why has the destruction of the Aral Sea been called the worst environmental disaster of the 20th century?

The destruction of the Aral Sea has been called the worst environmental disaster of the 20th century due to the severe and long-lasting impact on the ecosystem, agriculture, and human health in the region.

What is the significance of soil in the context of the Aral Sea disaster?

Soil is a living, dynamic, and precious substance that is deeply affected by land and resource management. The Aral Sea disaster highlights the consequences of mismanagement on soil health and overall ecosystem stability.

How does the composition of soil relate to its ability to support plant life?

Soil composition, which includes minerals, organic material, air, and water, is crucial for plant life. The right proportions of these components create a suitable environment for plants to thrive.

What are the different layers of a soil profile called and what are their functions?

The different layers of a soil profile are called soil horizons. They include the O horizon (rich in humus), the A horizon (topsoil with nutrients and organic material), the E horizon (where finer particles are leached away), and the B horizon (storage center for minerals and nutrients).

How do soil organisms contribute to soil health and biodiversity?

Soil organisms such as small mammals, earthworms, and microscopic organisms contribute to soil health by burrowing, aerating, redistributing soil, breaking down organic material, and binding soil particles together, thus supporting biodiversity.

What role does water play in the soil profile and why is it important for plant growth?

Water in the soil profile is crucial for plant growth as it absorbs minerals, becoming soil water that carries nutrients to plant roots. It also contributes to the soil's porosity, allowing for air and water balance necessary for plant life.

Why is soil conservation important and what are some of the challenges faced by soil scientists?

Soil conservation is important to prevent soil degradation and loss, which can lead to reduced agricultural productivity and ecosystem collapse. Soil scientists face challenges such as rapid soil erosion, salinization, and the need to manage soils sustainably for future generations.

Outlines

00:00

🌊 The Aral Sea Disaster

This paragraph discusses the environmental catastrophe that befell the Aral Sea, once one of the world's largest lakes. It was a thriving ecosystem until the Soviet era when it began to shrink due to the diversion of its feeding rivers for irrigation of cotton and rice fields. The water's rapid evaporation led to soil salinization, rendering the land infertile. The salinization also caused dust storms carrying pollutants over vast areas, further damaging the region's agriculture. The paragraph concludes with a reflection on the importance of soil as a living, dynamic resource and the need for proper land management.

05:02

🍰 Understanding Soil Composition

This section of the script uses the analogy of baking a cake to explain the complex composition of soil. It breaks down the components of soil, including minerals from parent material rocks, organic material or humus, and the importance of water and air. The script describes different soil layers, or horizons, starting from the organic-rich O horizon to the nutrient-rich A horizon, and further down to the less active C and R horizons. It emphasizes the biodiversity within soil and the crucial role of soil in the ecosystem, concluding with the importance of soil conservation and the work of soil scientists in preventing disasters like the Aral Sea's desiccation.

Keywords

💡Aral Sea

The Aral Sea, once one of the four largest lakes in the world, is a key example in the video illustrating the devastating effects of environmental mismanagement. It was reduced to a fraction of its size due to the diversion of its feeding rivers for agricultural use, leading to a massive ecological disaster. The script discusses how the sea's shrinkage led to salinization of the soil, which in turn affected the ability of plants to grow, highlighting the intricate balance of water resources and their impact on ecosystems.

💡Salinization

Salinization refers to the process where soil accumulates salts to a degree that it becomes unsuitable for plant growth. In the context of the video, it is a consequence of the Aral Sea's water being diverted, leading to the evaporation of water and the concentration of salts. The script mentions how salinization created a salty crust on the soil, preventing plants from absorbing water and nutrients, which is a critical environmental issue discussed in the video.

💡Soil Horizons

Soil horizons are layers within the soil profile, each with distinct characteristics. The video uses the metaphor of a cake to explain these layers, with the O horizon being the topmost layer rich in organic material, similar to the frosting on a cake. The A horizon, or topsoil, is likened to the cake's cream cheese layer, rich in nutrients. These horizons are crucial for understanding soil composition and function, as they determine the soil's ability to support plant life.

💡Humus

Humus is the organic component of soil, derived from decomposed plant and animal materials. It plays a vital role in supplying nutrients and influencing soil properties such as color, texture, and water retention. In the video, humus is compared to 'chunks of carrots and walnuts in a cake,' emphasizing its importance in soil fertility and structure. The script underscores the significance of humus in maintaining soil health and supporting biodiversity.

💡Erosion

Erosion is the process by which natural forces like wind and water wear away the Earth's surface, including soil. The video mentions erosion in the context of soil development on steep slopes, where water quickly flows downhill without being absorbed, leading to less developed soils. Erosion is a significant factor in soil loss, which is a major environmental concern highlighted in the video.

💡Laterization

Laterization is a soil-forming process that occurs in tropical rainforest climates, where intense weathering leads to the formation of laterite soils. These soils are rich in iron and aluminum oxides and are characterized by their brick-like hardness. The video uses laterization to illustrate how different climates and conditions lead to the development of distinct soil types, which is essential for understanding global soil diversity.

💡Calcification

Calcification is a soil-forming process where calcium carbonate accumulates in the soil, leading to the formation of hard layers like caliche. The video describes this process in the context of tropical grasslands and deserts, where calcium from grasses contributes to soil development. Calcification is a key concept in understanding how soils in arid regions are formed and how they differ from those in more humid climates.

💡Podzolization

Podzolization is a soil-forming process characterized by the leaching of organic acids from the upper soil layers, leading to the formation of ash-gray E horizons and the accumulation of organic matter in lower horizons. The video mentions podzolization in the context of coniferous forests, where the decomposition of pine needles contributes to soil acidity and the leaching of aluminum and iron compounds. This process is crucial for understanding the development of soils in boreal and subarctic regions.

💡Soil Biodiversity

Soil biodiversity refers to the variety of life forms that exist within the soil, including plants, animals, and microbes. The video emphasizes that a quarter of the planet's biodiversity is made up of soil organisms, which play critical roles in soil structure, nutrient cycling, and ecosystem health. The script highlights the importance of preserving soil biodiversity as a key component of sustainable land management and environmental conservation.

💡Soil Conservation

Soil conservation involves the practices and strategies aimed at preventing soil degradation and preserving its quality for future use. The video touches on the importance of soil conservation in the face of increasing soil loss and the need for sustainable land management. Soil scientists play a vital role in mapping and analyzing soil types, determining their suitability for various uses, and leading conservation efforts, as mentioned in the script.

Highlights

The Aral Sea was one of the four largest lakes in the world before 1960, covering 68,000 square kilometers.

The Amu Darya and Syr Darya rivers supplied water to the Aral Sea, supporting a lush ecosystem.

Cotton and rice fields during the Soviet era consumed most of the river waters, leading to the sea's shrinkage.

By the 1980s, the Aral Sea received only a small fraction of its former water supply, causing rapid evaporation.

Evaporation left behind salt, creating a salty crust that hindered plant growth.

The salinization process rendered the soil unusable for agriculture, despite the initial goal of increasing crop production.

Exposed sediment and pollutants from the shrinking sea contributed to massive dust storms.

The destruction of the Aral Sea is considered the worst environmental disaster of the 20th century.

Soil is a dynamic and precious substance, deeply affected by land and resource management.

Soil composition is complex, requiring a balance of minerals, organic material, air, and water.

Parent material, or rocks, forms the base of soil, influencing its texture and structure.

Humus, derived from living organisms, supplies energy and nutrients to the soil.

Soil profiles consist of layers called soil horizons, each with distinct properties.

The O and A horizons are rich in humus and organic material, supporting biodiversity.

Soil organisms, such as earthworms and microbes, play crucial roles in soil health.

Precipitation is essential for soil water, which carries nutrients for plant growth.

Soil air, the space between soil particles not filled with water, provides necessary gases for life.

The C horizon, or Regolith, is composed of partly broken down parent material.

The R horizon is the lowest layer, consisting of unbroken parent material or bedrock.

Soil development is influenced by climate, vegetation, topography, parent material, and time.

Soils are the foundation of life on Earth, supporting local ecosystems and agriculture.

World Soil Day is celebrated on December 5th to acknowledge the importance and vulnerability of soils.

Soils bridge the biosphere and lithosphere, forming a platform for life on Earth.

Soil scientists work to prevent disasters like the Aral Sea's destruction by studying and conserving soil.

Transcripts

Before 1960, the Aral Sea was one of the 4 largest lakes in the world and covered 68,000

square kilometers.

It was supplied by the waters of the Amu Darya and Syr Darya rivers, and the soil nearby

grew a lush variety of plants.

But during the Soviet era, fields of cotton and rice took over the region, using most

of the waters of these rivers and their tributaries.

And by the 1980s, only a trickle of new river water made it to the Aral Sea, so it began

to shrink.

As the liquid water molecules evaporated, they left behind all the salt that had been

dissolved in the water.

This salinization covered the newly exposed soil in a salty white crust, which then blocks

plants from being able to absorb water and nutrients.

In the nearby fields, Aral Sea water would still be pumped in for the crops, but rapid

evaporation continued to leave behind a thick crust of salt on the soil.

So the sea was being destroyed to grow crops, but the crops couldn’t grow because of more salinization.

As the Aral Sea continued to shrink and more sediment was exposed, salt and dirt -- along

with fertilizers, pesticides, and other pollutants that built up over time -- whirled into massive

dust storms and were transported far and wide.

All that stuff eventually spread over thousands of square kilometers and endangered valuable

cotton and other crops elsewhere in the region.

And what once was a fertile area by the Aral Sea looks like a desert with scrubby vegetation

and a salty crust coating the land.

The destruction of the Aral Sea has been called the worst environmental disaster of the 20th century.

And one moral of this real-life parable is that soil is a living, dynamic, and precious

substance that’s deeply affected by how we manage our land and resources.

With the right composition, care, and natural cycling, soil supports entire ecosystems -- so

we shouldn't take it for granted.

I’m Alizé Carrère and this is Crash Course Geography.

Soils bring together all four spheres of physical geography, and understanding soil composition

is kind of like baking.

Like a rich carrot cake that needs just the right amounts of flour, water, spice, carrot,

and cream cheese frosting to make a delicious treat, soils are a complex collection of minerals,

organic material, air, and water in just the right proportions for plants to thrive.

The flour in our soil cake is the parent material -- rocks that are broken down by plants, animals,

wind, and water.

The size of these rock particles determines a soil’s texture and structure.

Like sandstone is very strong, so it makes a chunky, coarse textured soil.

All the non-living inorganic soil minerals come from the parent material rocks.

So we usually end up with elements commonly found in rocks like silicon, aluminum, oxygen and iron.

And we get different compounds of those elements as chemical processes break down the rocks.

Unlike the inorganic minerals, the organic material in soil, or humus, comes from living

things like leaves and partly decomposed plants and animals.

Humus supplies energy and nutrients and influences the color, texture, structure, and chemical

properties of a soil and how much water and air it can hold.

The organic material is like chunks of carrots and walnuts in our cake.

And just like in a cake, the right amount of water and air help create the perfect texture.

Let's cut a wedge of our soil cake to see how it all comes together.

This slice is a soil profile with layers called soil horizons that each have different properties.

On the surface is the O horizon made of some of that humus, like extra chopped walnuts

we sprinkle on top of our cake.

Soils rich in humus are “workable” which means they have good porosity or capacity

for holding water.

Below this is the A horizon, commonly called topsoil, which is like the top layer of our

cake with a rich cream cheese frosting slathered on top.

It has tons of nutrients and decomposed organic material.

[So like if we lived in an ideal world where frosting is nutritious.]

The O and A horizons hold a vast hidden world of biodiversity or all different plants, animals,

and microbes that exist.

In fact, a quarter of our planet’s biodiversity is made up of soil organisms in the ground.

Small land mammals burrow and redistribute the soil, earthworms aerate soil and improve

soil structure, and microscopic organisms break down organic material, hold important

nutrients, or bind soil particles together.

But this teeming life in soils wouldn’t be possible without precipitation, just like

a cake would be dry without liquids.

Water absorbs minerals in the soil and becomes soil water, carrying nutrients farther down

so plants can absorb them with their roots.

Any extra soil water that beads and sticks to soil particles is called capillary water,

which plants can use during dry periods.

But soil water doesn't stop at plant roots -- it can filter down to deeper levels and

keep leaching, or depleting, the nutrients from the topsoil.

A well-made cake is moist but also light and fluffy, so the spaces between soil particles

not filled with water hold soil air, which supplies oxygen and carbon dioxide necessary

for life.

Below the A horizon are layers of basically all the extras from the topsoil.

Certain soils have an E horizon made up of coarse sand and silt.

Here, finer clay and iron oxide particles are leached and carried even farther down

with the soil water.

This process is eluviation, which is where the E comes from.

All leached materials from the A and E layers accumulate in the B horizon which is kind

of like the storage center for minerals and nutrients that get leached down.

Scientists usually only use the word "soil" to talk about the A through B horizons.

That’s where plant roots are and the layers actively change through interactions with

weather, nutrients, plants, and animals.

But our full soil cake is bigger.

The next layer is the C horizon or Regolith, which comes from partly broken down parent

material.

This layer is pretty unaffected by all the stuff happening above, and finding plant roots

or even soil microorganisms here is pretty rare.

And the R horizon is the lowest layer, made of unbroken parent material or bedrock.

It's kinda like the plate the cake sits on, if the plate were made of hardened flour or

something much older than the soil.

The inorganic minerals and rocks in upper layers might’ve come from breaking down

some of the bedrock, or they could’ve been carried by

streams, glaciers, waves, and wind from far away.

A soil profile is a complicated recipe to develop, [but I think Paul Hollywood would

give us “star baker.”

And maybe even the Hollywood Handshake.

In a non-cake ecosystem, a few centimeters of prime farmland soil may require 500 years

to gather nutrients and build a rich topsoil.

But from Iowa to China, Peru to Ethiopia, and the Middle East to the Americas the topsoil

is being worn away faster than new soil can form, and there are record levels of soil

loss happening as of 2021.

Plants can’t grow and entire economies are changing, like from the salinization of the

Aral Sea.

It’s a hard problem that we’ve given soil scientists who are kind of like doctors, and

look after soils to prevent such disasters from happening again.

They map and analyze soil types, determine their suitability for different uses, and

lead conservation efforts using science from all sorts of fields like physics, mineralogy,

hydrology, climatology and more.

To best understand the way to protect soils, understanding the different characteristics

of soil across Earth can help.

Like if we could walk along the 20 degree meridian, we’d see many specific soil forming

processes as we moved between climates.

We’d start in the shady cool of the Congo rainforest under a dense canopy of tall trees.

In this rainforest climate, rocks break down rapidly and minerals are

decomposed as part of a chemical process called laterization.

We call the soil that forms laterite, meaning “brick-like,” because it’s mostly a

hardened B horizon made of iron-rich clay mixed with quartz and other minerals.

In fact, it’s so hard it’s used as building material.

Moving north, we find ourselves in the tropical grasslands, which transition into semi-desert

scrub, and then the true desert of the Sahara as there’s less and less moisture.

In climates like these where there’s not a lot of moisture for trees to grow but grasses

thrive, the soil forms through calcification.

Over thousands of years, calcium carbonate leaches down to the B horizon and creates

a hard layer called caliche.

And more calcification happens as grasses draw up calcium from the A horizon and return

it to the soil when they die.

Crossing the Mediterranean Sea and heading into the Alps, the topography or the shape

of the land influences soil development.

Like on steep slopes, water quickly flows downhill without absorbing into the soil.

And because of increased erosion, soils also have less time to develop.

The Sun also plays an interesting role in the highland climates of the mountains.

South-facing slopes in the Northern Hemisphere that receive the Sun’s rays at a steeper

angle are warmer, and their soils are drier.

After crossing the Alps, we reach the coniferous forests of northern Europe.

Here the soil forms from podzolization which is a word that comes from the Russian word

“podzol” which means “ashy.”

As pine needles decompose, they make the soil more acidic, which leaches out aluminum and

iron compounds from the A horizon.

The remaining silica gives the E horizon a distinctive ash-gray color.

That was just one little stretch of one meridian, but even there no two soils are alike.

And their development and distribution depends on spatial factors like climate, vegetation,

topography, parent material, and time.

No matter where we are, soils are the foundation of life on Earth, from the local ecosystems

of plants and animals, to the crops we grow and food we eat.

Good fertile soils are like gold we seek out at any risk -- like planting crops in the

shadows of volcanoes or in the flood zone on the banks of rivers.

The UN food and agriculture organization celebrates December 5th as World Soil Day because soil

should be celebrated, but also because our soils are at risk.

Soils are a bridge between all four of Earth's physical geography systems, but especially

the biosphere and the lithosphere, or Earth’s solid realm which forms a platform for plant,

animal and human life.

The lithosphere is shaped by internal and external processes that build it up and wear

it down, and we’ll start exploring that next time when we look at how rocks and minerals

are formed.

Many maps and borders represent modern geopolitical divisions that have often been decided without

the consultation, permission, or recognition of the land's original inhabitants.

Many geographical place names also don't reflect the Indigenous or Aboriginal peoples languages.

So we at Crash Course want to acknowledge these peoples’ traditional and ongoing relationship

with that land and all the physical and human geographical elements of it.

We encourage you to learn about the history of the place you call home through resources

like native-land.ca and by engaging with your local Indigenous and Aboriginal nations through

the websites and resources they provide.

Thanks for watching this episode of Crash Course Geography which is filmed at the Team

Sandoval Pierce Studio and was made with the help of all these nice people.

If you want to help keep all Crash Course free for everyone, forever, you can join our

community on Patreon.