Three main types of weathering: physical weathering, chemical weathering and

biological weathering.

Chemical weathering- physical breakup of rocks with no change in chemical composition. Includes Agents: water, ice, wind, temperature changes.

Physical weathering- Dissolving of minerals present in the rock, these are removed leaving the rock to break

apart more easily.

Biological weathering- The movement of plant roots forcing its way into small cracks of rocks, exerting pressure

and causing the rocks to break.

In the Sedimentation test- The gravel settles first at the bottom because it is less dense than the others. It is

less heavier and larger.

Soil crumbs- clumps of soil created by humus which improve aeration and drainage in

heavy wet soils.

Air is not needed for aerobic respiration in decomposers. Decomposers are not needed to release nutrients needed by plants.

Black soils are rich in organic materials (humus) meaning very fertile. Red soils are rich in iron compounds.

Sandy soil- Large particles with spaces between them that traps a little air, and retains lot of water.

Loam- a mixture of sand, clay, silt and humus. Very fertile soil which is excellent for plant

growth.

Erosion is the process in which the topsoil in the presence of trees is removed by water and wind.

Bodies of living organisms (plants and animals) contain oxygen, carbon, hydrogen, nitrogen and many other elements.

When Organisms excrete elements in the form of gases, faeces and urine, this is the only way that elements can be recycled.

When the living organisms die decomposers break down the organic compounds in the body into smaller ones. Decomposers also help break down other wastes such as faeces.

The main process that releases oxygen into the air is respiration.

Combustion of fuels can produce another compound- carbon monoxide.

Carbon passes as carbon dioxide from the air into plants in the process of respiration some is returned by the process of photosynthesis.

Decomposers release carbon as carbon dioxide when they decay dead plants, animals, faeces and urine.

In the water logged soil where there is not enough oxygen in the soil, there are bacteria that change the nitrates back to nitrogen. These bacteria are called Nitrogen Fixing bacteria.

Crust- the outer layer which is very thin between 5 and 67 km thick and consists of the land and the sea.

The mantle is the center of the earth which consists of heavy metals. It has an inner and an outer layer. The outer layer consists of molten rocks, iron and nickel and it is about 2000 km thick.

The earth's crust is not a continuous layer made up of pieces called Plates.

Earthquakes are generally felt as a sudden trembling movement in the sea.

The magnitude of an earthquake and be measured on the Richter scale. The Richter scale varies in magnitude from 0 (no movement) to 9 (extreme movement).

Earthquakes and Tsunamis have nothing in common.

A tsunami is caused by an abrupt vertical shifting of the seafloor which disturbs the water above it.

Volcanoes are associated with the edges of tectonic plates. Occur when there is a built up of heat and pressure beneath the earth’s crust caused by hot molten rocks (magma) only.

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth.

As air masses move over the surface of the Earth, they cause changes in weather. The boundary where air masses meet are called faults.

A cyclone is a general name given to all types of storms. It is an area of low pressure in the atmosphere which is accompanied by windy and rainy weather.

Hurricanes are tropical cyclones which have wind speeds greater than 38 mph.

The centre of the hurricane is called the eye.

Tropical storms have wind speeds of 74 mph and greater.

Cyclones occur when different air masses meet. For example when warm, moist air from the tropics meets with cold, dry polar air either a warm or cold front results.