Soil is a mixture of weathered rock, organic matter, water, and air that supports the growth of plant life. Organic matter (decomposed leaves, twigs, roots, and other material)

Factors Affecting Soil Formation

1. Parent rock being weathered. When limestone is chemically weathered it leaves behind clay. This produces clayey soil. When sandstone is chemically weathered, it leaves behind sand which produces sandy soil.
2. Topography (surface features) - on steep hillsides, soil rarely develops because rock fragments are constantly moving down the hillside. In lowlands (where land in flat), wind and water deposits fine sediments that form thick soils.
3. Climate - if rocks weather quickly, deep soil develops rapidly. This is more likely to happen in tropical areas where the weather is warm and moist. Climate also affects the amount of organic material in the soil. Soils in desert climates have little organic material because there are few plants and animals to decompose. In humid areas, where vegetation (plants) is plentiful, the soil has more organic material. When plants and animals decompose, a dark colored material forms called humus. Most of the organic material in soil is humus. The humus helps soil hold water and provides plants with nutrients to grow.
4. Time - It takes time for rocks to weather and soil to form. young soil resembles its parent rock while older soil looks less like the parent rock.
5. Organisms - organisms can add or take away from the nutrients in soil. Lichens are small organisms that consists of alga and fungus. Lichens can grow on rock and take nutrients from the rock. The rock begins to break down forming a thin soil. After the soil has formed, many types of plants can grow.

Ice

When ice in a glacier becomes thick enough its weight causes it to flow downhill; it becomes an agent of erosion. As glaciers move over the Earth's surface they erode material in some places and deposit sediment in others. There are two kinds of glaciers: continental glaciers and valley glaciers.

Glacial Erosion - glaciers can erode rock in two different ways. (1) If the underlying rock has crack in it the ice is able to pull out pieces of rock. This causes slow erosion in the rock. The looses pieces of rock freeze into the bottom of the glacier and are dragged over the Earth's as the glacier moves. (2 ) They scratch the Earth (rock) below like giant pieces of sandpaper. This scratching is another way that glaciers can erode rock. Scratching makes large grooves or small scratches in the rock beneath. It can also grind the rock into a fine powder called rock flour.

Effects of Glacial Erosion - Glaciers are capable of reshaping Earth's surface. Valley galciers are able to remove rock from mountain tops. This leaves behind large bowls, called cirques and steep peaks. When a glacier moves into a stream valley it erodes rock along the valley sides making a wider U shaped valley. Continental glaciers can move through large lakes and completely remove rock layers from the land's surface.

Glacial Deposition

Glaciers can also deposit sediment. When glaciers stop moving and begins to melt or when ice melts at the bottom of a flowing glacier, the sediment the ice was carrying along the bottom of the ice gets left behind on the Earth's surface. Sediment deposited directly from glacier ice is called till. Till is a mixture of of different sized particles, ranging from clay to large boulders. Glaciers increase melting during summer months. So much water can melt that streams can form that flow away from the glacier. These streams deposit sediment. Sand and gravel deposits from these streams are called outwash. The outwash consists of particles that are all about the same size.

Evidence

As glaciers move, they pick up pieces of sediment and carry them with it scratching rocks. Glaciers can also thaw slightly and then refreeze over a mountain top. Once the glacier moves it pops the top off the mountain. This is known as a cirque. Finally, as glaciers move, they push and carry sediment and large rocks or boulders carving our a U shaped valley.

Water

Water that flows over Earth’s surface is known as runoff. Runoff causes erosion; especially when the water is moving fast. The more speed water has the more sediment it can carry.

1. Sheet Flow - As raindrops hit the Earth, they break up clumps of soil and loosen small grains of sediment. On a sloped land surface, a thin sheet of water may begin to move downhill. Water flowing downhill in a thin sheet is known as a sheet flow. Sheet flows can carry loose sediment grains causing erosion of the land. Erosion due to sheet flow is called sheet erosion.

2. Rills & Gullies – When sheets of water flow around obstacles and become deeper rills can form. Rills are small channels cut into the sediment Earth’s surface. These channels can carry more sediment than sheet flow. As runoff flows through the rills, the sediment erodes the channel even more and causes it to widen and deepen. When the channels gets to be about 0.5 meters across they are called gullies.

3. Streams – Gullies usually connect to stream channels. Streams can be small enough for you to step over or large enough for barges to transport products along their course. In mountainous / hilly areas streams have quite a bit of energy and the rushing water can cut into the rock beneath the stream. As streams flow back and forth through the valley, they erode and deposit sediment along the way. Streams shape more of the Earth’s surface than ice, wind, or gravity. Streams can have enough power to cut large canyons into the Earth. When rivers / streams enter an ocean or lake, large amounts of sediment are deposited from the slowing water. This accumulation at the mouth of the lake / ocean is called a delta.

Water deposition can cause deltas. When a stream or river meets a larger body of water (ocean), it slows down and drops the sediment that it is carrying causing a delta to form.