The main components of soil are ____ (from decaying plant and animal material) and fragments of rocks. Soil formation results from chemical and physical ____ of rocks, along with ____. During a ____ the particles of soil settle out according to particle size, where the larger and heavier particles settle out first (to the bottom of the container).Humus improves the crumb structure of soil, allowing for proper aeration and ____ without becoming ____. The three main types of soil are sand, clay and ____. ____ depends on particle size, mineral content, ____ and soil pH. ____ is a process in which topsoil is removed either by wind or water. The Earth consists of three main layers: the core, ____ and crust. The Earth’s crust is divided into large ____. The sudden trembling or movement of the Earth indicates that an ____ is occurring. ____ are cracks along which rocks slip. The vibrations of an earthquake are greatest at the ____. A ____ measures the intensity of the vibrations of an earthquake. The ____ of an earthquake can be measured on the ____. Submarine earthquakes may result in ____. ____ result when there is a build-up of heat and ____ beneath the Earth’s surface. Molten ____ is called ____ when it reaches the Earth’s surface. The three basic types of volcanoes are ____, shield and ____ (strato-volcano). Volcanoes are classified as active, dormant or ____ depending on their ____. ____ is the fast-moving dense mixture of volcanic gases, rock fragments, ____ and hot ash down the side of the volcano. Tides result from the ____ pull of the Moon and Sun on ____ on the Earth’s surface. When the Moon, Earth and Sun are in line ____ are formed. ____ are formed when the Moon and Sun are at ____ to one another in relation to the Earth. There are four types of air masses: maritime tropical (mT), ____ (cT), maritime polar (mP) and ____ (cP). When two air masses meet, the boundary between them is called a ____. There are four types of fronts: cold front, warm front, stationary front and ____ front. A cyclone is a region of low pressure accompanied by wind and rain, e.g. a storm or hurricane. A cyclone is classified as a ____ when the wind speeds exceed 120 km/h. The ____ of a hurricane is a region of calm.

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