Wind and water can erode rocks, such as sea cliffs, with which they come in contact.
Geology is the scientific study of the Earth's evolution from its creation 4.6 billion years ago to the present day. It comprises all physical and chemical processes that contribute to the creation, composition and structure of rocks. This involves the study of earthquakes, volcanoes, sedimentation and erosion. It includes the investigation of changes in flora, fauna and climate over the 4.6 billion year geological record. Applications of modern geology include exploration for hydrocarbons and minerals, stone aggregates and building materials. Environmental protection, urban development and waste disposal require knowledge of geologic processes and principles.
Temperature
High temperatures cause rocks to heat up and expand. The heat penetrates only a surface layer of the rock that flakes away in the process. Sharp changes of temperature create thermal stress within the rock and make it expand and contract. This stress splits rocks along joints or lines of weakness and eventually, disintegrates the rock mass.
Precipitation
Rain falling towards Earth dissolves carbon dioxide in the atmosphere and produces a mildly acidic solution. When this falls on limestone rocks, it creates grooves and ridges as the rain dissolves the rock material. Rainfall dissolves feldspar, a silica compound that is present in all rocks and is the most common mineral in the Earth's crust, and transforms it into clay.
River Flow
Water accumulates in rivers as a result of precipitation and snow melt. Rivers flow downhill and carve out steep-sided valleys. They carry sediments downstream and deposit them in plains and deltas. A river flood plain is a flattened valley floor where the river meanders in a snake-like fashion, eroding rock and sediment on its convex side, and depositing sediment on its concave side.
Glaciation
A glacier moving down a mountain side.
Glaciers are rivers of ice are the powerful version of precipitation. They are able to cut and carve through rock to form sharp ridges of rock and broad U-shaped valleys. A glacier forms in the freezing temperatures at the top of high mountain ranges. As it moves down the mountain, it carries a mixture of broken rocks and soil until it reaches a lower elevation and higher temperatures where it melts. Ice ages are periods of global cooling when sheets of ice cover whole continents and move from the Earth's North and South Poles towards the Equator. The Earth was entirely covered in ice during the Permian -- Triassic mass extinction period that occurred between 290 million and 252 million years ago. The ice cover caused the extinction of 95 percent of the Earth's species.
Wind
Wind blows sand and sculpts exposed rocks. It reworks particles of rock into smaller pieces, carries them as sand and dust, and deposits them in another location. In desert regions, wind transport creates moving sand dunes. After wind erosion, rocks are more vulnerable to penetration by water and ice.
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