5 THE COMPOSITION OF THE EARTH AND ITS ATMOSPHERE AND THE PROCESSES OCCURRING WITHIN THEM SHAPE THE EARTH’S SURFACE AND ITS CLIMATE

Cryosphere, lithosphere and biosphere

Into the cryosphere we include all the ice and snow on the earth‘s surface, such as glaciers, snow layers and permafrost (i.e., permanently frozen ground). As we indicated above, snow can reflect a large amount of solar radiation (high albedo).

Lithosphere

The lithosphere is the upper part of the Earth‘s crust. We include here the surface of the land , but also the seabed. There are considerable differences in oceanic and continental crust, especially in thickness and composition. The thickness of the mainland crust is approximately 35 km in diameter and consists of three layers. The lower layer consists mostly of basalt, middle granite and transformed rocks and the upper layer is formed by sediments. The ocean crust is thinner compared to the mainland – roughly 5–10 km thick. In terms of composition, it consists of similar layers to the mainland, except for the granite layer.

Different rock layers contain different fossils (the key to dating the geological past). Fossils are made up of the remains of animals or plants that lived in a previous geological period. Thus, fossils provide information on the relative and absolute age of rocks, as well as traces of previous geological events, climate and evolution of the earth. Rocks are naturally occurring aggregates consisting of one or more minerals. They consist of material that has been present on Earth since its formation, with the exception of material that originates from meteorites. In the process of rock formation we can talk about so-called. a rock cycle that illustrates the transformation of rocks over time (one cycle may last several million years).

In this cycle, rocks are transformed by various processes that take place at two points – at or near the earth‘s surface (weathering, erosion and deposition) and deep below the earth‘s surface (melting, elevated pressure, high temperature).

Pic 47: Rock cycle
(Diagram source: http://creation.com/the-rock-cycle)

Rock cycle

The above diagram shows the rock cycle. The converted rock will become magma upon heating (up to the melting point). If it got into the environment, where it would start to cool and gradually crystallize, a drilled (igneous) rock would be formed. To become a settled rock, it must undergo several processes, such as weathering and erosion, which break it down into smaller pieces or fragments. When this sediment accumulates, compresses and solidifies, it becomes a solid rock (so-called sedimentary rock). Over time and under the influence of heat and pressure, this rock becomes a converted rock. The straight arrows within the rock cycle diagram indicate that each rock type can be converted to any other rock type by going through several processes.

The Earth‘s surface is affected by various processes, which are divided into external (operating above the earth‘s surface) and internal (operating below the earth‘s surface).

External processes

External processes include:

1. Weather conditions: disintegration of rocks into smaller pieces (helps to formate soil):

  • Physical weathering – the rock breaks into smaller fragments by physical agents, e.g. when water penetrates cracks in rocks where it freezes. When solidified, the water increases in volume, causing the rock to break.
Pic 48: Physical weathering 
(Picture source: https://www.geo.fu-berlin.de)
  • Chemical weathering – decomposition of rocks caused by changes in their chemical composition. Changes occur when the rock is exposed to air or water. E.g. Rainwater, together with carbon dioxide, creates a weak acid that dissolves certain minerals in rocks.

2. Erosion: the process of removing and carrying away rock material on the Earth‘s surface:

  • Gravitation and water – gravity causes water to move from the slope. Flowing water erodes the surface on which it passes.
  • Iceberg – slowly moves down the slope, grinding and removing pieces of rock.
  • Wind – the wind disrupts the soil surface and subsequently carries away the disrupted particles that are stored elsewhere.

Internal processes

Internal processes that take place beneath the earth‘s surface create e.g.:

  • Mountains – formed by orogenisis and strike faults. Orogenisis are caused by forces in the Earth‘s crust, which press the rocks from the sides, causing the layers to bend into folds. In this way, ridges and valleys are formed. Strike faults are created when forces in the earth‘s crust compress or push the rock until it breaks. The rock then slides along a crack or fracture. The break length can range from a few meters to hundreds of kilometers. The units separated by a break are called blocks.
Pic 49:  Geological Strike Fault 
(Picture source: http://web.gccaz.edu/~lnewman/gph111/
topic_units/fold_fault_eq/fold_fault_eq2.html; http://geol.jex.cz/menu/geologicke-struktury)
  • Earthquakes – caused by strong vibrations as the rock blocks move on the tectonic fracture.
  • Volcanos – to put it simply, these are holes in the earth‘s crust through which lava flows from the underground. The lava cools to form a solid rock.

Soil Composition

The soil is located between the surface and mother rock. It is divided into layers with specific physical, chemical and biological characteristics. The soil consists of several components. About 50% of the volume is due to pores containing soil air and soil solution (water) and 50% to mineral and organic matter. The mineral part constitutes 95–99% of the solid soil component. On the other hand, the organic part accounts for only 1–5%.

Mineral content of soil is characterized by mineralogical, chemical and granular soil composition. Organic soil content consists of living organic substances (e.g. roots of growing plants) and inanimate organic substances (humus, dead plant residues, animals).

Pic 50: Soil composition
(Picture source: https://www.vectorstock.com/royalty-free-vector)

Soil species

The soils are divided according to the percentage content of the individual grain fractions into so-called Soil species. Several national and international classifications are compiled for this purpose. In the Slovak environment, the Novak classification is used, which classifies soils into 7 species according to the coarse clay content (fraction below 0.01 mm) (Representation of soil species, 2017):

Kernkategorien

Partikelgehalt <0,01 mm

Darstellung in %

Erdboden leicht

– Sand (0 – 10%)
– Lehm-Sand (10 – 20 %)

 6,4

Erdboden mittleres Gewicht

– Sand-Lehm (20 – 30 %)
– Lehm (30 – 45 %)

 73,2
Erdboden schwer
 – Klei-Lehm (45 – 60 %)

17,1

Erdboden sehr schwer

– Keil (60 – 75 %)
– Tone (75 > %)

3,3
  • Light soils – contain a clay component up to 20%. It is soil with a predominance of sand particles. They can heat up very quickly but also cool on the surface. They heat up quickly, but also cool. In terms of permeability, we consider them to be the most permeable soils (for more details see the following table). They dry up very quickly and humus is formed to a lesser extent.
  • Moderate soils – contain clay component from 20-45%. This type of soil provides the most suitable conditions for the growth of most plants. Water leaks into it very easily.
  • Heavy soils – clay component is more than 45%. This type of soil is considered to be the least permeable.

The biosphere, which includes all living organisms, is closely related to the lithosphere. Vegetation prevents the reflection of large amounts of sunlight (low albedo). In addition, photosynthesis affects the exchange of gases between the surface and the atmosphere and affects the evaporation of water.