Category Earth Science

Rocks go through many changes over time. These are caused by different processes, such as heating, cooling, and weathering. The sequence of changes is called the rock cycle.

Igneous rock:

Igneous rocks form by the cooling of magma (molten rock material beneath the surface) or lava (molten rock material extruded onto the surface). Magma which originates at depths as great as 200 kilometers below the surface consists primarily of elements found in silicate minerals along with gases, notably water vapor. Because the molten material is less dense than the surrounding solidified rock, it works its way toward the surface where it flows out onto the surface as lava.

Cooling:

What would you do to turn a melted chocolate bar back into a solid? You’d cool it by putting it into the refrigerator until it hardens.

Similarly, liquid magma also turns into a solid — a rock — when it is cooled. Any rock that forms from the cooling of magma is an igneous rock. Magma that cools quickly forms one kind of igneous rock, and magma that cools slowly forms another kind. 

When magma rises from deep within the earth and explodes out of a volcano, it is called lava, and it cools quickly on the surface. Rock formed in this way is called extrusive igneous rock. It is extruded, or pushed, out of the earth’s interior and cools outside of or very near the earth’s surface. 

What if the magma doesn’t erupt out of a volcano, but instead gets pushed slowly upward toward the earth’s surface over hundreds, thousands, or even millions of years? This magma will also cool, but at a much slower rate than lava erupting from a volcano. The kind of rock formed in this way is called intrusive igneous rock. It intrudes, or pushes, into the earth’s interior and cools beneath the surface. 

Melting:

What happens to a chocolate bar when it gets very hot? It melts.

The same thing happens to a rock when it is heated enough. Of course, it takes a lot of heat to melt a rock. The high temperatures required are generally found only deep within the earth. The rock is pulled down by movements in the earth’s crust and gets hotter and hotter as it goes deeper. It takes temperatures between 600 and 1,300 degrees Celsius (1,100 and 2,400 degrees Fahrenheit) to melt a rock, turning it into a substance called magma (molten rock). 

Metamorphic rock:

Metamorphic rocks are formed by the alteration of pre-existing rocks from exposure to heat and pressure while remaining in a solid form. Metamorphism occurs by breaking bonds between atoms in a mineral so that the atoms rearrange themselves into new, more stable, mineral forms. Rocks are transformed and remain in a solid state because not all the bonds in the rock’s minerals are broken – if they were the rock would melt.  Metamorphism occurs in solid rock because only some of the bonds between atoms are broken in an unstable mineral. As a result, the freed atoms and ions can migrate to another location within the mineral, or bond with atoms in a different mineral. The end result is to produce minerals that are more stable under the environmental conditions in which they exist. 

Metamorphism involves the transformation of a pre-existing rock to form new minerals and textures. The original mineral content of a rock can change in several ways. Unstable minerals like clay will breakdown and their elements will recombine to form new minerals. More stable minerals like quartz, will stay quartz but change shape and size to form a new configuration. At high temperatures, atoms and ions may move into a new orientation and bond into more stable forms. Hence, the type of minerals and its texture may change but the chemical composition of the rock itself can stay the same.

Uplift:

Understanding the idea of Uplift is the key to making sense of the rock cycle, as it allows us to see rocks that were once deeply buried beneath the surface.

If rocks did not get uplifted to form hills and mountains, then the processes of weathering and erosion would long ago have reduced much of the world’s land-masses to low-lying, flat plains. Weathering and erosion, transport and deposition would all effectively stop.

Scientists believe that, if all these active processes of the rock cycle ceased to operate, then our planet would cease to be able to support any life.

Mount Everest is made of limestone that must have originally formed on an ancient sea floor because it contains fossils of marine creatures.

Heat and Pressure:

The atoms in rocks rearrange to form bigger and heavier minerals. The combination of heat and pressure may cause the minerals in the rock to split into layers. Metamorphic rocks begin changing at temperatures of 100 degrees Celsius to 800 degrees Celsius. If you squeeze and heat a rock for a few million years, it can turn into a new kind of rock. 
The pressure comes from many layers of rock piling on top of each other, and the heat comes from magma.  It’s like putting blankets on yourself – the more you layers you put on, or the more blankets you put on, the more pressure you receive because of all the weight of the layers on top of you.

Sedimentary rock:

Sedimentary rocks are those formed from the compaction and cementation of fragments of pre-existing rocks called clasts, or plant and animals remains. The exogenic processes of weathering and erosion create the raw materials for sedimentary rocks. Earth material is loosened and moved from higher to lower elevations where it is deposited as transportation agents like water, wind or gravity lose their energy to move sediment. Streams and rivers transport sediment to lakes or oceans, or deposits it on nearby floodplains where it accumulates. On land, clastic sediments consist mainly of large boulders, cobbles, gravel, sand, and silt. On the continental shelves at the margin of continents, marine sediment is largely sand, silt, and clay. At the outer shelves and on the ocean floor, clays and chemically precipitated calcium carbonate and the remains of tiny marine animals accumulate.

Weathering and erosion:

Rocks are hard and strong, but they do not stay that way forever. Forces like wind and water break down rocks through the processes of weathering and erosion.

Weathering is the process that breaks down rocks. Many things cause weathering, including climate changes. Erosion breaks rocks down further and then moves them. Forces like wind and water move the rock pieces. They mix with matter like sand to become sediment. Weathering and erosion help shape Earth’s surface. They are part of a process called the rock cycle.

Transportation and deposition:

Eroded rock particles are carried away by wind or by rain, streams, rivers, and oceans. As rivers get deeper or flow into the ocean, their current slows down, and the rock particles (mixed with soil) sink and become a layer of sediment. Often the sediment builds up faster than it can be washed away, creating little islands and forcing the river to break up into many channels in a delta.

Sedimentation and cementation:

Cementation, in geology, hardening and welding of clastic sediments (those formed from preexisting rock fragments) by the precipitation of mineral matter in the pore spaces. It is the last stage in the formation of a sedimentary rock. The cement forms an integral and important part of the rock, and its precipitation affects the porosity and permeability of the rock. Many minerals may become cements; the most common is silica (generally quartz), but calcite and other carbonates also undergo the process, as well as iron oxides, barite, anhydrite, zeolites, and clay minerals.

 

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Soil is made up of broken rocks, minerals, decaying plants and animals, tiny creatures, gases, and water. If a section is cut through soil, you will see many layers. The depth of the layers vary in different soils.

Humus:

Humus, nonliving, finely divided organic matter in soil, derived from microbial decomposition of plant and animal substances. Humus, which ranges in colour from brown to black, consists of about 60 percent carbon, 6 percent nitrogen, and smaller amounts of phosphorus and sulfur. As humus decomposes, its components are changed into forms usable by plants.

Topsoil:

It is also called the humus layer, which is rich in organic material. This layer consists of decomposed material and organic matter. This is the reason; the topsoil has a dark brown color. The hummus makes the topsoil soft, porous to hold enough air and water. In this layer, the seeds germinate and roots of the plants grow. Many living organisms like earthworms, millipedes, and centipedes, bacteria, and fungi are found in this layer of soil.

Leaching layer:

Leaching, loss of soluble substances and colloids from the top layer of soil by percolating precipitation. The materials lost are carried downward (eluviated) and are generally redeposited (illuviated) in a lower layer. This transport results in a porous and open top layer and a dense, compact lower layer. The rate of leaching increases with the amount of rainfall, high temperatures, and the removal of protective vegetation. In areas of extensive leaching, many plant nutrients are lost, leaving quartz and hydroxides of iron, manganese, and aluminum. This remainder forms a distinctive type of soil, called laterite, or latosol, and may result in deposits of bauxite. In such areas rapid bacterial action results in the absence of humus in the soil, because fallen plant material is completely oxidized and the products are leached away. Accumulations of residual minerals and of those redeposited in lower layers may coalesce to form continuous, tough, impermeable layers called duricrusts.

Weathered rock:

Weathering is the name given to the process by which rocks are broken down to form soils. Rocks and geological sediments are the main parent materials of soils (the materials from which soils have formed). There is a very wide variety of rocks in the world, some acidic, some alkaline, some coarse-textured like sands, and some fine-textured and clayey. It is from the rocks and sediments that soils inherit their particular texture. When you see rocks in the landscape it is easy to appreciate how long the process of breaking down rocks to form soil takes. In fact, it can take over 500 years to form just one centimetre of soil from some of the harder rocks. Fortunately, in some respects at least, huge amounts of rocks were broken down during the Ice Age over 10,000 years ago and converted into clay, sands or gravels, from which state it was easier to form soils.

Subsoil:

It is comparatively harder and compact than topsoil. It is lighter in color than the topsoil because there is less humus in this layer. This layer is less organic but is rich in minerals brought down from the topsoil. It contains metal salts, especially iron oxide in a large proportion. 

 

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Soil is the layer of loose material between the surface and the solid rock below the ground.  Chances are that you haven’t thought a lot about the soil under your feet, but you may be surprised at the complexity of soil. Soil varies in its composition and the structure of its particles, and these factors are closely examined by farmers, who need appropriate soil for planting crops, as well as engineers who may need to understand how soil is going to hold up under different demands. Soil is also vitally important to the sustainability of an ecosystem because it serves as the natural medium for the growth of vegetation. Nothing can grow on Earth without it, but the soil varies in different places.

Grasses:

The soil is rich in nutrients, so many grasses can grow healthy and quickly.  They are an important source of food for man; they play an important ecological role in nature; and they are good protectors of the soil against soil erosion. The greatest value of grass is perhaps the role that grass plays in stabilizing and protecting the soil and for this reason the grass family is probably the most important plant family on earth.

Long roots:

Trees and grasses have long roots that go deep down to collect as much water as possible from the soil. Roots grow through the whole life of the plant. They grow longer from the tip, adding cells to the end of each root. The root adds cells to their tips, and they grow fatter as they add cells around their tube-like bodies.

At the tip of each root, there is a small group of tough, dead, hard cells called the root cap. The root cap is the strongest part of the root tip, and its job is to push its way through the dirt to look for moisture and nutrients and protect the plant.

Dung beetle:

These creatures feed on and break up, or decompose, animal poo, adding nutrients to the soil. Dung beetles aerate and mix the soil by burrowing, and increase the organic matter content of the soil by burying dung. These changes improve the water holding capacity and nutrient availability of the soil, with associated benefits to plants. By burying dung, they also provide an important food source for decomposers, and reduce resources for the larvae of economic insect pests such as bushflies

Leafcutter ants:

Ants dig tunnels into the soil, letting in air and moving around decaying plants and animals, which add nutrients to the soil. Leaf-cutting ants modify soil fertility through two mechanisms. First, the building, enlargement, and maintenance of nests ants affect soil structure, porosity and density. Second, leafcutters collect and concentrate vegetal material inside their nests to maintain their fungus culture, the food for most of the colony. As a result of this process, ants generate a huge quantity of organic waste that is deposited in nest cavities or dumps on the soil surface.

Buttress roots:

Trees have shallow roots underground to quickly take in the water and nutrients in the topsoil. Most rainforest soil is very poor with all the nutrients available largely remaining at surface level. Because of this rainforest trees have very shallow roots. 

Some very tall trees have developed ways of obtaining much needed additional support by forming buttressed roots, which grow out from the base of the trunk sometimes as high as 15 ft above the ground. These extended roots also increase the area over which nutrients can be absorbed from the soil.

Forest floor:

Many leaves from the thick tree canopy fall to the dark forest floor and decay. The major compartments for the storage of organic matter and nutrients within systems are the living vegetation, forest floor, and soil. The forest floor serves as a bridge between the above ground living vegetation and the soil, and it is a crucial component in nutrient transfer through the biogeochemical cycle. Much of the energy and carbon fixed by forests is periodically added to the forest floor through litterfall, and a substantial portion of the nutrient requirements of forest ecosystems is supplied by decomposition of organic matter in the forest floor and soil surface. 

Autumn leaves:

As the weather gets cooler and the days get shorter in the fall, trees start to prepare for winter. Trees use sunlight to make a special layer or seal between each leaf and the branch it is connected to. Then the leaves fall easily to the ground, leaving the branches of the tree protected from the cold that will come in the winter and also helping the tree store up food!

Since leaves have water inside their cells, they can’t survive freezing temperatures, because the water would freeze and the leaves would die. When leaves fall to the ground, they eventually break down and provide nutrients for the soil, helping prepare for more plants to grow in the spring and also create a layer that helps the ground absorb water.

Earthworm:

Earthworm burrows alter the physical structure of the soil. They open up small spaces, known as pores, within the soil. When earthworms are introduced to soils devoid of them, their burrowing can lead to increases in water infiltration rates of up to 10 times the original amount. This brings water and soluble nutrients down to plant roots. Burrowing also improves soil aeration (important for both plants and other organisms living in the soil) and enhances plant root penetration.

Tree roots:

Tree roots absorb nutrients and water from the soil. Large roots anchor the tree into the ground to prevent it from blowing over in the wind. Most roots live just 6-12 inches below ground and extend far beyond the width of the tree’s canopy. Cutting tree roots can cause stress to a tree and can leave it vulnerable to disease or insect attack. Roots need oxygen. By allowing soil to dry for several days between watering, oxygen can make its way to the roots. Avoid piling new soil or compacting the ground underneath the tree. This can suffocate the roots that absorb oxygen close to the surface. 

 Cactus:

Cacti have shallow roots and thick stems, so they can collect and store water. Cacti can have many small, thin roots near the top of the soil. These roots take in water quickly after a rain. The same cactus may have one long, thick root called a taproot. The taproot grows deep in the soil. It can reach water when the soil on top is dry.

Deep roots:

Desert trees have very long roots to reach down and collect water from deep underground. There are several benefits to a deep root system rather than a large surface root system. A deep root system helps the plants stay grounded in the soil through harsh winds and other adverse conditions. And the plant is not dependent on rainfall to get water for survival.

Kangaroo rat:

When burrowing, animals break down large rocks, mix up the soil, and let air into it. Kangaroo rats play an important in the ecological communities in which they live. Specifically, they influence plant growth by feeding on and dispersing seeds and digging burrows in the soil. This contributes to the overall health of their ecosystem. They are also prey for numerous predators, including barn owls, burrowing owls, snakes, and coyotes. In order to help keep ecosystems healthy, we have worked with our partners to translocate kangaroo rats out of areas that are slated for development and into appropriate habitat on protected reserves.

Grassland:

The soil is usually deep and full of nutrients. This is because rotting grass roots help to hold the soil together and add nutrients for new plants. Plants compete for water. Grasslands occur in environments conducive to the growth of this plant cover but not to that of taller plants, particularly trees and shrubs. The factors preventing establishment of such taller, woody vegetation are varied.

Tropical rainforest:

The soil is very wet and many plants grow, so there is lots of humus to add nutrients to the soil. However, these nutrients are washed away by the constant rain, leaving shallow, acidic soil. Most tropical rainforest soils relatively poor in nutrients. Millions of years of weathering and torrential rains have washed most of the nutrients out of the soil. More recent volcanic soils, however, can be very fertile. Tropical rain forest soils contain less organic matter than temperate forests and most of the available nutrients are found in the living plant and animal material. Nutrients in the soil are often in forms that are not accessible by plants.

Constant warmth and moisture promote rapid decay of organic matter. When a tree dies in the rainforest, living organisms quickly absorb the nutrients before they have a chance to be washed away. When tropical forests are cut and burned, heavy rains can quickly wash the released nutrients away, leaving the soil even more impoverished. 

Temperate deciduous forest:

The soil is moist and full of nutrients from decaying plants and animals, especially in autumn. The deep roots of plants break up the bedrock, which adds minerals. Water often drains through steadily.
The soil of deciduous forests is classified as an alfisol or a brown forest soil.  It is very nutrient rich. This is caused by the large leaf fall during the fall seasons.  When the snow melts in the spring the leaves on the ground decompose and supply the nutrients that the plants need to grow.  This type of soil was considered the most fertile type of soil until the modern inventions allowed other types of soil to be modified.

Desert:

The soil is very dry and few plants grow, so there is little humus. It is made up of boulders, pebbles, and sand, and is blown around by the wind. Any water drains through the sand easily. Deserts soils are generally of brown, light brown or reddish color. Due to arid conditions, leaching of soil is almost absent in the desert soils and thus evaporation is quite rapid.

Therefore, these soils are in general saline. Further in some low level areas, the salt content in the desert soil is really high. In fact, it is so high that common salt is obtained by evaporating the saline water collect from such areas.

However, salt content in some desert soils is not that high and thus in such cases they support vegetation in the sufficient availability of water. Moreover, in some areas land is rocky and is surrounded by gravel.

 

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Spectacular Angel Falls is the world’s tallest waterfall. With a drop of 979 m (3,212 ft), it is more than twice the height of New York’s Empire State Building. American pilot Jimmy Angel first spotted the waterfall from the air in 1933.

Lying within the Canaima National Park, Angel Falls is part of the plateau that underlies the lands located in Venezuela to the south of the Orinoco River. The plateau’s age is estimated at two billion years. Important geological transformations can be seen at the park, from its beginnings in the Precambrian period dating back to the time of the formation of the super continent Pangaea.

This continent began to separate due to the formation of a fracture in the planet’s crust resulting in the formation of the Atlantic Ocean, and the creation of different portions of lands called shields. The geographic region in Venezuela, known as the Guyanese Shield, existed from the start as a great plain at an elevation roughly as high as today’s visible tepuis, about 6500 to 9800 feet. After the formation of the great plain, during a long period of time—approximately 400 to 200 million years ago—a series of climate-related phenomena caused important changes in the geography of the Guyanese Shield.

The transformation of the landscape was due to drastic variations of arid climate to humid and vice versa; of strong, constant and lingering precipitations; droughts, freezing, discharges with high and low temperatures; storms, hurricanes, and the tectonic movements of the earth. The erosion was caused by atmospheric agents removing the material deposited in the great plain during millions of years. In places where the rock was less resistant, the erosion was greater resulting in this great transformation, the Tepuis, and the fantastic scenery at the Falls.

 

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Covering 1,000 km (600 miles), Atacama Desert, Chile South American desert is one of the driest places on Earth. Some parts have not seen rainfall since records began at least 400 years ago! The northern part of the Atacama Desert contained valuable minerals. Bolivia and Chile attempted to claim the area in the 1800s, causing the War of the Pacific from 1879 to 1884. Chile claimed victory and won control of the region. The extreme ecosystem of the Atacama makes survival difficult for animals. However, red scorpions, grey foxes, desert wasps and butterflies are among the species able to cope with the dry environment. You can also find penguins, sea lions and pelicans nearer the Pacific side.

The Atacama Desert was at the centre of the world’s attention in 2010. Famous for the ‘Copiapo mining accident’, whereby 33 miners survived a record 69 days buried in a 120-year-old copper-gold mine. Thankfully, all 33 miners were safely rescued on 13th October 2010. Often compared to the planet Mars, the Atacama’s landscape and soils are unique. Its appearance is unlike other deserts and several movies and television programmes have been filmed in the area. One of the most famous of which is A Space Odyssey. The Atacama Desert is one of the top three destinations for visitors to Chile. The other top attractions include Easter Island and Chile’s Lake District.

 

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Krubera Cave, Georgia is the world’s deepest cave lies in Asia, Stretching down 2,197 m (7,208 ft), it is nearly as deep as seven of Paris’s Eiffel Towers. Russians call the cave Voronya, meaning “crow’s cave”, after the many crows nesting at the entrance.

Krubera Cave is a deep, mostly vertical cave system. Passages in the cave system can be narrow and difficult to pass or wide and very large. In order to explore the caves completely cave divers need to be prepared to put on scuba gear because tunnels in the caves can sometimes become flooded. Flooded tunnels are referred to as sumps. Some of the passageways in Krubera Cave had to be widened to make it possible for cave divers and explorers to venture further.

 

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The world’s longest river is the Nile, at 6,825 km (4,238 miles) in length. It flows through 11 African countries, from Burundi to Egypt, where it meets the Mediterranean Sea. The Nile takes its name from the Greek for “river valley”.

The availability of water from the Nile throughout the year, combined with the area’s high temperatures, makes possible intensive cultivation along its banks. Even in some of the regions in which the average rainfall is sufficient for cultivation, marked annual variations in precipitation often make cultivation without irrigation risky.

The Nile River is also a vital waterway for transport, especially at times when motor transport is not feasible—e.g., during the flood season. Improvements in air, rail, and highway facilities beginning in the 20th century, however, greatly reduced dependency on the waterway.

 

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The peak of Mount Everest lies 8,848 m (29,029 ft) above sea level, making it the world’s highest mountain. It is ten times taller than the world’s tallest building- the Burj Khalifa skyscraper in Dubai.

Mount Everest attracts many climbers, some of them highly experienced mountaineers. There are two main climbing routes, one approaching the summit from the southeast in Nepal (known as the “standard route”) and the other from the north in Tibet. While not posing substantial technical climbing challenges on the standard route, Everest presents dangers such as altitude sickness, weather, and wind, as well as significant hazards from avalanches and the Khumbu Icefall. As of 2017, nearly 300 people have died on Everest, many of whose bodies remain on the mountain.

 

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If a stalagmite and stalactite become long enough and meet, they will form a rocky column. Columns are also created when a stalactite grows down to touch the cave floor.

As compound cave formations, they include among their ranks the tallest free-standing speleothems in the world. (Certain flowstone falls–sheets of calcite lining vertical shafts–are undoubtedly taller, but rarely measured). The towering specimens of the upper left photo, from Ogle Cave in Carlsbad Cavern National Park, New Mexico, USA, are indeed impressive. These, however, are only about half as high as the 61-meter tall column in Tham Sao Hin, a cave in Thailand.

 

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These thin, hollow tubes also form from dissolved particles in water, dripping slowly through the roof of a cave. They may grow into stalactites if the water keeps dripping for a very long time.

These tubes form when calcium carbonate or calcium sulfate dissolved in the water comes out of solution and is deposited. In soda straws, as each drop hovers at the tip, it deposits a ring of mineral at its edge. It then falls and a new drop takes its place. Each successive drop of water deposits a little more mineral before falling, and eventually a tube is built up. Stalagmites or flowstone may form where the water drops hit the cave floor.

Soda straws are some of the most fragile of speleothems. Like helictites, they can be easily crushed or broken by the slightest touch. Because of this, soda straws are rarely seen within arms’ reach in show caves or others with unrestricted access. Kartchner Caverns in southern Arizona has well-preserved soda straws because of its recent discovery in 1974 and highly regulated traffic.

 

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