## Theory

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# Shields

A shield is an ancient piece of the Earth's crust where rocks of over 500 milion years old have surfaced. These old rocks surface because the material on top has been removed by the processes of weathering and erosion.

(IASbaba, 2018)

Within Russia there are two of those shields:

- The Baltic Shield
  This shield roughly covers the European part of Russia and it is geologically stable.
- The Siberian Shield
  This shield is located in the north(-eastern) part of Russia and it is geologically unstable. The Siberian Shield has been uplifted several times over the past millions of years. The magma that flowed upward through the faults often contained valubale minerals. This is why Siberia is rich in all kinds of ores.

# Soils

Soil is the uppermost layer of the Earth's crust, in the Netherlands to about 1.20 metres deep. Some type of soils have very distinctive layers, these layers are called horizons. The formation of the horizons is caused by the climate and vegetation on the surface.

- In a warm climate, there are more organisms living in the soil. These organisms break down the plant matter that reaches the ground, e.g. fallen leaves, dead plants, etc. Therefore the humus (part of the soils formed by decomposed plant and animal matter) gets broken down easily. Which lead to a thinner top layer with humus, see podzol.

In a wet climate, where there is more precipitation than evaporation, the water dissolves the humus and minerals from the ground (eluviation) and puts those down deeper in the ground (illuviation).
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(De Boer et al., 2023)

With in Russia two types of soils are predominant:

- Podzol
  This soil can be identified by the clearly visible horizons and the presence of an eluvial (light grey) and illuvial (darker coloured) zone.
- Chernozem (black earth or soil)
  This soil can be identified by the lack of visible horizons and thick layer of black earth.

Other examples of soils, as seen in the figure above, are the latosol and desert soil.

- Latosol
  This is the type of soil found in tropical rainforests. The red colour is caused by a high iron content. And it has a very thin fertile top layer, making the soil in total very infertile.
- Desert soil
  This soil is found in deserts. At top of this soil you can find a slat crust, because it rain so little and there is so much evaporation, that only the minerals within the rain stay behind.

# Permafrost

Permafrost is soil that is permanently frozen. In Russian it is sometimes refered to as merzlota. A few characeristics of permafrost are:

- It is located in area where it is always cold;
- The closer to the arctic, the thicker the layer;
- The top layers thaws in summer;
  - The meltwater cannot flow deeper into the ground, because it is still frozen;
  - This muddy period in summer gets called rasputitsa (time without roads);
- The tundra turns into marsh with mosses, grasses and low shrubs.

The melting of the permafrost also plays a role in the greenhouse effect:

- Plant remains in the frozen ground do not decompose, because oxygen cannot reach.
- The melting releases oxygen, which enables the decomposition of plant remains, which releases greenhouse gases.
- The melting releases large amounts of greenhouse gases, e.g. methane and carbon dioxide.

(EEA, 2017)

# Fertile Triangle

Within Russia, there are many factors that play a role in the inability to use the ground for agricultural purposes: the permafrost, the cold climates, the infertile soils. This leaves a relatively small portion of Russia's territory suitable for agriculture. This area is called the Fertile Triangle and it spans from Odessa (in Ukraine), to Saint Pertersburg, to Irkutsk.