Soil Formation and Continental Drift
Soils
Soil Formation
Soil is formed by the very slow weathering of rocks.
In spaces between rock pieces, air and water enter, creating an environment for various life forms.
Living organisms and their waste contribute to decomposition through the action of bacteria and fungi.
Substances produced by decomposition combine with minerals, forming new dark minerals called humus.
Soil formed in the same place where weathering occurs is called indigenous soil.
Chips and particles resulting from weathering are carried by water or wind to other areas where they accumulate and form a soil termed aloctono.
Soil Components
| Soil Components |
|---|
| Humus |
| Water and mineral salts in solution along with suspended clay particles |
| Clay particles |
| Fine sand |
| Gravel |
Soil Types
Sandy soils: Rough to the touch, mostly composed of large particles (from stone to sand). Large pores allow water to pass through easily. These permeable soils do not flood but lose moisture quickly.
Clay soils: Soft to the touch, dominated by very fine clay particles. These particles form a tight aggregate with tiny pores, making them impermeable. Water passes through with difficulty, and they flood easily.
Organically rich soils: Balanced portion of coarse and fine particles. Intermediate permeability and texture. These are the best soils for crops.
Soil Water
Pore water: Found in spaces between soil particles. Plant roots absorb it.
Hydroscopic water: Strongly adheres to soil particles. Released at temperatures above 100°C. Utilized by plants.
Soil Properties
Permeable: Water passes easily through pores.
Low permeability: Water passes slowly.
Waterproof: Water does not pass.
A Moving Earth
Plate Tectonics
Internal pressures and high temperatures within the Earth cause the crust to break into masses called tectonic plates.
These plates move, and hot, elastic mantle material rises to the surface through the space between separating plates. This new crust pushes older crust to the sides, widening the crust, primarily in the oceans, and causing continental drift.
As plates collide, landslides, elevations, and folds occur, causing earthquakes and tsunamis.
When molten mantle material erupts violently to the surface, volcanoes form. The cooled lava around the mouth creates the characteristic conical shape.
Continents are zones of plates emerged above sea level. As plates move, continents shift closer or further apart.
Continental Drift
225 million years ago: A single continent, Pangea, and a vast ocean, Panthalassa, existed.
180 million years ago: Pangea began breaking apart, forming Laurasia and Gondwana, separated by the Tethys Sea.
65 million years ago: Gondwana broke apart, forming the Atlantic Ocean. North America connected to Eurasia, and India separated from Eurasia.
Present day: India joined Asia. The Americas, Asia, and Australia are separate continents. Antarctica is isolated.
In 50 million years: Australia will be closer to the Americas. Asia and Africa may separate. The Atlantic Ocean will be the largest, and the Pacific the smallest.