Geological processes, such as plate tectonics, erosion, chemical weathering, and sedimentation, shape the Earth’s surface and are studied by geologists to understand the planet’s history, locate resources, and predict disasters. Plate tectonics drives the movement of continents and explains the formation of mountain ranges and volcanic activity. Erosion, caused by water, ice, and wind, transforms landscapes and forms features such as river valleys and gorges. Chemical weathering and sedimentation also contribute to the formation of rocks and fossils, which help reconstruct the history of life on Earth.
The term “geological processes” describes the natural forces that shape the physical structure of a planet. Plate tectonics, erosion, chemical erosion and sedimentation are all examples of forces that significantly affect the earth’s surface and explain its main characteristics. These processes are closely studied by geologists and earth scientists to improve their understanding of the planet’s history; to help locate useful resources, such as metal ores; and to aid in the prediction of potentially disastrous events, such as earthquakes, tsunamis and volcanic eruptions.
Plate tectonics
Looking at the Earth from space gives an impression of total, immovable serenity. The history of the planet, however, is dominated by the splitting and joining of landmasses to form new continents that continually change their positions. These geological processes are driven by plate tectonics and occur on timescales too long for humans to appreciate directly. The earth’s crust is made up of solid “plates” of rock floating on denser, but semi-liquid, material underneath. Convection currents in this material, known as the mantle, cause these plates, which form the continents, to move over time.
Sometimes, continental plates collide with each other, forming mountain ranges like the Himalayas. Plates can also split, as is happening today in the African Rift Valley. If the planet could be seen as it was about 250 million years ago, it would be very different from its current appearance. It is thought that, at that time, all the continents were united into one huge “supercontinent” that researchers call Pangea. About 200-225 million years ago, driven by tectonic processes, this landmass began to break up into smaller pieces, eventually forming the modern continents.
Tectonic processes can also bring continents together. Some geologists think that the Earth has gone through several cycles in which huge landmasses split to form smaller continents which later merged back together again. There may have been a number of previous supercontinents.
The earth’s crust consists of two layers: continental crust and, beneath it, oceanic crust, which is composed of denser rocks. Oceanic crust is exposed beneath the oceans. Beneath the Atlantic Ocean, new material is rising from the mantle to form a mid-ocean ridge as America and Europe move further apart. In other areas, including the west coast of South America, oceanic crust is sinking beneath continental crust in what’s called a subduction zone. The friction produced by this process has led to volcanism in this area, forming the Andes mountain range.
Plate tectonics explains why earthquakes and volcanic activity tend to occur around the edges of continents. These are areas of greatest geological activity, where subduction or the movement of continental plates against each other can result in violent events. Unfortunately, large numbers of people live in geologically active areas near plate boundaries, but humans are beginning to develop the means to predict disasters. By closely monitoring things like small rock movements, fractures and bulges in the ground, scientists can sometimes issue advance warnings of earthquakes and volcanic eruptions.
An understanding of the geological processes involved in plate tectonics can also help locate valuable mineral resources. The material of the continental and oceanic crusts and mantle varies in its mineral composition. Geologists can plot plate boundaries and map the probable locations of different types of crust and mantle rock. Combining this with knowledge of the melting points of minerals and the sequences in which they crystallize, it might be possible, for example, to guess the probable location of a copper ore deposit within a large mass of solidified magma.
Erosion
When rock is worn away by water, ice, or even wind, it is called erosion. It is one of the most important geological processes and, over time, can transform landscapes. Sand and grit particles carried by water or wind have an abrasive effect and can sculpt rock into new shapes on a large scale. Some of the most dramatic land features are produced by ice in the form of glaciers. Grits and rock fragments embedded in the ice scrape against the rock, altering the landscape on a massive scale.
The uplift of land caused by the collision of two continental plates combines with the forces of erosion to form mountain ranges such as the Himalayas or the Alps. Water forms river valleys, helping to shape the mountain range, but as land rises high enough for permanent snow, glaciers form. These slow-moving rivers of ice carve steep, flat-bottomed valleys, narrow ridges, and sharp, pyramidal peaks, producing the mountain ranges most people know today. The Matterhorn in the Swiss-Italian Alps is a classic example of a pyramidal peak.
Running water also has a major impact on landscapes. It forms river valleys and gorges, depending on the nature of the terrain. One of the most spectacular examples of water erosion is the Grand Canyon, a mile-deep gorge (about 6,000 feet or 1.83 km) that scars the Arizona landscape. It was formed over a period of approximately 17 million years.
Wind erosion can also contribute to landscape formation, although usually on a smaller scale. Features caused by this form of erosion are usually found in very dry areas. Wind can remove loose material from the ground, forming depressions that can be quite large, such as the Qattara depression in Egypt. Windblown grit and grit can produce small-scale landscape features, such as yardangs, long smooth ridges aligned with the normal direction of the wind.
Chemical weather
The rock can react with the substances present in the water or in the air, producing chemical atmospheric agents. When rocks that form deep underground are exposed at the surface, they can slowly change color and crumble due to, for example, iron compounds reacting with oxygen in the air. The resulting, weaker material may begin to form soils or may be eroded and deposited elsewhere.
Another common example is the dissolution of limescale by acidic water. Water can be acidified by organic compounds or by absorbing volcanic gases. Limestone consists largely of calcium carbonate, which reacts easily with acids. Caves and sinkholes are common results of chemical weathering of limestone. Inside the caves, stalagmites and stalactites form over time through the dripping and evaporation of water containing dissolved rock material.
The sedimentation
Material suspended or dissolved in water forms rock by a process known as sedimentation or deposition. This can occur through the accumulation and compaction of small particles as they settle out of the water or by evaporation causing crystallization of dissolved chemicals. Rocks formed in this way are called sedimentary rocks. Examples include sandstone, which forms from grains of sand; limestone, which consists of the shells of small organisms; and salt and chalk deposits, which form from the evaporation of water containing these minerals. Sometimes, sedimentary rocks can build up into layers several kilometers thick.
Sedimentary rocks can contain fossils, which are much more likely to be preserved in this type of rock than those that have been subjected to high temperatures. Geologists and paleontologists have been able to reconstruct a history of life on the planet by analyzing sedimentary rocks and fossils. Fossilized marine organisms found on mountain tops far from the sea were an early indication that rock movement, both horizontal and vertical, had taken place on a large scale at some time in the past. It was the similarities in fossils of a certain age on different continents that ultimately led to the theory of plate tectonics.
The hypothesis that a meteorite impact may have caused the extinction of the dinosaurs has emerged from the discovery of a layer rich in the rare metal iridium in sediments dating from around the time of the extinction. This layer is found in widely separated parts of the world where rock of the right age is exposed, suggesting that it likely came from an external source that caused an event that had an extremely large impact.
Protect your devices with Threat Protection by NordVPN
