My Science School

When lichen and moss growing on a rock create an environment that causes rocks to break down both physically and chemically.

Biological weathering also means organic weathering. It is the disintegration of rocks as a result of the action by living organisms. Plant and animals have a significant effect on the rocks as they penetrate or burrow into the soil respectively. Biological weathering can work hand in hand with physical weathering by weakening rock or exposing it to the forces of physical or chemical weathering.

For instance, some plants and trees grow within the fractures in the rock formation. As they penetrate into the soil, and their roots get bigger, they exert pressure on rocks and make the cracks wider and deeper that weaken and eventually disintegrate the rocks. Microscopic organisms can also produce organic chemicals that can contribute to the rock’s mineral weathering.

Biological weathering is a very common type of weathering that we see around us. There are many small animals that bore hole in the rock and live inside it. Over the time, they burrow and widen cracks and end up breaking rocks apart. Then there are bacteria, algae and lichens produce chemicals that help break down the rock on which they survive, so they can get the nutrients they need. They produce weak acids which convert some of the minerals to clay. We, humans, are also responsible for biological weathering. As we construct more homes, industries, dams, power plants, roads, we rip the rocks apart.

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When water collects in the cracks of a rock, it can freeze when temperatures drop. The ice expands and the pressure can split the rock. In cold, mountain regions, one can even hear gunshot-like cracks as rocks are split apart by frost.

A mechanical process, freeze-thaw weathering causes the ?joints?(cracks) in rocks to expand, which wedges parts of rocks apart. Because water expands by about 10% when it freezes, this creates outward pressure in rock joints, making the cracks larger.

Joints occur naturally in rocks as a result of their formation. Fractures that are not offset, joints do allow for the entry of water into rocks.

In climates where temperatures dip below freezing in the winter, moisture in the joints of rocks solidifies as ice. Over time, after several cycles of freezing and thawing, joints get large enough that bit of rock start to fall off in smaller pieces. This breakdown of rock happens faster at higher altitudes, where many freeze-thaw cycles can occur during the year.

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When water collects in the cracks of a rock, it can freeze when temperatures drop. The ice expands and the pressure can split the rock. In cold, mountain regions, one can even hear gunshot-like cracks as rocks are split apart by frost.

A mechanical process, freeze-thaw weathering causes the joints? (cracks) in rocks to expand, which wedges parts of rocks apart. Because water expands by about 10% when it freezes, this creates outward pressure in rock joints, making the cracks larger.

Joints occur naturally in rocks as a result of their formation. Fractures that are not offset, joints do allow for the entry of water into rocks.

In climates where temperatures dip below freezing in the winter, moisture in the joints of rocks solidifies as ice. Over time, after several cycles of freezing and thawing, joints get large enough that bit of rock start to fall off in smaller pieces. This breakdown of rock happens faster at higher altitudes, where many freeze-thaw cycles can occur during the year.

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Physical weathering is also known as mechanical weathering. It is a process, initiated by humans, plants or animals, which breaks down rocks and minerals on the surface of Earth. It changes just the shape or size of the rocks and minerals. Chemical weathering, on the other hand, happens when the chemical composition of the rock and soil changes, forming new chemical combinations and a different internal structure.

Physical weathering is also called as mechanical weathering. This is the process where rocks breakdown without altering their chemical composition. Physical weathering can occur due to temperature, pressure or snow. There are two main types of physical weathering. They are freeze thaw and exfoliation.

Freeze-thaw is the process where water goes into the cracks of the rock, then freezes and expands. This expansion causes rock to break apart. Changing temperature also causes rocks to expand and contract. When this happens over a period of time, rock parts starts to break down. Due to the pressure, cracks can be developed parallel to the land surface which leads to exfoliation.

Physical weathering is prominent in the places where there is little soil and few plants. For example, in desserts surface rocks are subjected to regular expansion and contraction due to temperature changes. Also, in mountain tops, snow keeps melting and freezing which causes physical weathering there.

Chemical weathering is the decomposition of rocks due to chemical reactions. This changes the composition of the rock. This often takes place when rain water reacts with minerals and rocks. Rain water is slightly acidic (due to dissolution of atmospheric carbon dioxide, carbonic acid is produced), and when the acidity increases chemical weathering also increases. With the global pollution, acid rains occur now, and this increases chemical weathering more than the natural rate.

Other than water, temperature is also important for chemical weathering. When the temperature is high, the weathering process is also high. This releases minerals and ions in rocks into surface waters. There are three main types as to how the chemical weathering occurs. They are solution, hydrolysis and oxidation. Solution is the removal of rock in solution due to acidic rain water. This is sometimes called carbonation process, since the rain water acidity is due to carbon dioxide. Hydrolysis is the breakdown of rock to produce clay and soluble salts by acidic water. Oxidation is the breakdown of rock due to oxygen and water.

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Decaying leaves and plant matter give out carbon dioxide, which is also present in the air around us. Carbon dioxide dissolves in water to create carbonic acid through a process called carbonation. This acid can, over time, dissolve rocks, especially limestone. Limestone is a soft rock that consists mainly of calcium carbonate, which reacts with rainwater, dissolving away to create huge caves and cave complexes.

Carbonation is the chemical reaction between carbon dioxide present in the air, and the hydration compounds of the cement in concrete structures. The rate of carbonation depends on the physical characteristics such as the design, on-site preparation, production and protection, as well as external factors, such as the location and degree of exposure to contaminants and other environmental factors. Carbonation may lead to the corrosion of the reinforcement steel and deterioration of concrete structures.

The carbonation process starts immediately when concrete is exposed to air. Carbon dioxide (CO2) penetrates the concrete through the pores where it reacts with the calcium hydroxide and the moisture in the pores to form calcium carbonate. The carbon dioxide combines with the pore water to form a dilute carbolic acid which acts to reduce the concrete’s alkalinity.

Carbonation reduces the concrete’s natural alkalinity from pH13 to about pH8. Whereas a high pH provides a passivation layer around the steel, at pH below 9.5, the passivation layer breaks down and exposes the reinforcement steel to the corrosive effects of water and air.

When steel rusts, it expands in volume and exerts force on the surrounding concrete, causing the concrete to crack and spall at a rate that increases exponentially if the corrosion is not prevented.

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Yes, trees can break up large rocks. Seeds may be deposited in the cracks and gaps of rock clusters and they germinate there. As the plant grows, the roots crack the rock further and may even break it into many pieces.

Plants can cause mechanical and chemical weathering. When plants cause mechanical weathering, their roots grow into rocks and crack them.It can also happen in streets or sidewalks. When plants cause chemical weathering, there roots release acid or other chemicals, onto rocks, which then forms cracks, and breaks apart.

Plants can cause physical weathering as their roots grow. Seeds of plants or trees can grow inside rock cracks where soil has collected. The roots then put pressure on the cracks, making them wider and eventually splitting the rock. Even small plants can cause this kind of weathering over time.

Biological Weathering - This type of weathering is caused by plants and animals. The plants and animals have acids inside them and when they release their acid it converts into chemicals that further results in weathering and breaking down of rocks and minerals and other types of landforms.

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The Indian red scorpion does not go after people, but it certainly needs to be feared. It is considered the most lethal scorpion in the world, and it will sting to defend itself. This can be dangerous, especially to little children.

These scorpions appear to prefer humid tropical and subtropical habitats, and are found in India, Pakistan, and Nepal etc. 2 to 3-1/2 inches long, they can be coloured from bright reddish orange to dull brown. They have small pincers, a thick tail and of course a large stinger.

The Indian red scorpion is a night hunter, which subdues prey using its chelae (claws) and stinger. It usually preys on small invertebrates like cockroaches, but sometimes will go for small vertebrates, too, like lizards and rodents.

Even though fearsome, the toxin of the Indian red scorpion has many uses in medicine.

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The funnel-web spiders get their name from their webs which are shaped like a funnel. The funnel’s mouth opens wide, and the spider sits patiently in the narrow part. When an insect prey touches the web, the spider rushes out to capture it. At least 40 species have been identified among these spiders, several of them carrying highly toxic venom. Especially dangerous is the male of Atrax robustus, or the Sydney funnel-web spider, which has caused many deaths. It has become part of Sydney’s folklore. An antivenom for its toxin was introduced in 1981.

Funnel-web spiders mainly live in eastern Australia, in the moist forest regions and highlands. They can be from 1 cm to 5 cm in body length, with the females more heavily built than the males. The front part of their body is covered with a carapace which is sparsely haired and glossy, and the colour of the body can vary from black to brown.

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The coastal taipan has very powerful venom, though not quite as strong as that of its cousin, the inland taipan. Anyway, these coastal snakes are more dangerous to humans than their more toxic relatives, because they live in areas where more people live. The coastal taipan’s venom is considered as the third most toxic among all the land snakes. Effective anti-venom for this was developed in the mid-1950s, and before that a bite from the taipan meant sure death.

The coastal taipans are found along northern Western Australia and the Northern Territory, along the Queensland coast. They live in a range of green habitats from forests to open grasslands, thriving particularly well in sugarcane fields where there are lots of rodents to feed on. These snakes hunt mostly during the day, using their sharp eyesight, but when it gets too hot, they will hunt at night too.

The coastal taipan is Australia’s longest venomous snake, some of them measuring up to 3 metres.

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‘Boomslang’ literally means ‘tree snake’, in Afrikaans and Dutch. As the name suggests, the boomslang snakes prefer to live in areas with trees wooded grasslands, arid savannas, lowland forests, etc. They are found in sub-Saharan Africa, mainly in Botswana, Swaziland, Namibia, Mozambique and Zimbabwe. They live on the trees and are active during the day. Extremely agile, they are very adept at climbing trees and gliding through the branches while hunting. The boomslang is a very dangerous, venomous snake. When the weather gets too cold, they take long, deep sleeps inside enclosed bird-nests.

The boomslangs can be of different colours, though most have a bright green colour.

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Meet someone who’s peaceful and shy – but take care, he’s considered among the most venomous snakes in the world!

The inland taipan is common to the semi-arid regions of central east Australia. Its venom is considered to be the most toxic among all snakes. In spite of the deadly weapon they carry, these snakes are usually shy and like to be left alone. But they defend themselves fiercely, when provoked or harmed. First the snake raises the front of its body in an S-shaped curve, to make a warning display. If the adversary ignores this warning, it will strike instantly and accurately.

These shy inland snakes have a relative in the coastal regions, the coastal taipans, which are aggressive.

The blue-ringed octopus may look cute and harmless at the first glance. But take care; it is an extremely poisonous animal!

These small octopuses are common in coral reefs and tide pools of the Pacific and Indian Oceans. They usually stay hidden in crevices, shells or marine debris, their tan-coloured body blending in with the surroundings. But the ‘true colour’ of this shy little thing comes out when threatened by somebody. Bright blue rings appear all over its body as a warning signal, which have given it the name.

If a human is bitten by the blue-ringed octopus it can cause respiratory distress and paralysis and other symptoms too, like nausea, blindness and heart failure.

The venom is not just to fight the enemies, it helps in feeding too. These octopuses usually hunt small crabs and shrimp, but will also eat molluscs and small fish. The octopus delivers the paralyzing venom into the prey. The venom is produced by its saliva, which also contains digestive enzymes. So the flesh of the prey is partially digested before the octopus sucks it out. The blue-ringed octopus is not hurt by its own venom.

The box jellyfish feeds on prey like fish and shrimp, but it does not want their escape struggles to damage its delicate tentacles. So the jellyfish uses its powerful venom to stun or kill the prey instantly. The venom of the box jellyfish is among the most deadly in the world, attacking the heart, nervous system and skin cells. Humans struck with this venom sometimes go into shock and drown before reaching shore. The survivors have to endure intense pain for weeks, and carry scars where the tentacles touched. These jellyfish do not fire venom at anything that the tentacles touch. The stinging cells only react to some chemicals on the skin, so there’s no wastage of their weapon!

Also known as sea wasps and marine stingers, these deadly jelly-fish mostly live in the coastal waters near Northern Australia and in the Indo-Pacific. The box jellyfish are so named because of their cube-like shape. This group include various species of various sizes; the largest measuring about a foot across, and with tentacles about ten feet long. Some divers use tight-fitting clothes that cover the whole body to escape their venom.

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The Mediterranean Sea holds a wonder that beats all – something that never dies! It is a jellyfish whose scientific name is Turritopsis dohrnii.

Jellyfish start their lives as larvae, which attach themselves to a suitable place like a rock. Then they are transformed into polyps that have a small body with tentacles. These polyps then clone themselves to form others and create a colony, or a medusa, which is the jellyfish.

When this jellyfish dies, or is physically damaged, the decaying cells form new polyps, and later return to their jellyfish state. This way they could live forever under the right conditions! However, they don’t actually achieve immortality because these tiny wonders are eaten by fish or other animals, or die by other means.

Although the jellyfish has ‘fish’ in its name, it is not fish. It is not made of jelly either. Unlike a fish, it is an animal without a backbone found in oceans and seas around the world. The name jellyfish derives from the jelly-like bodies of these animals. Jellyfish are found in oceans and seas all over the world, in the deepest as well as in shallow water.

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Meet someone whose body tells his own life’s story that runs into centuries! The ocean quahog, a bivalve mollusc that can live more than 500 years, is the longest-lived solitary animal.

The shell of an ocean quahog is a treasure-house of information for scientists. Its shell grows periodically throughout life and the growth patterns visible on the shell function as a calendar. They help not only to tell the age of the animal, but also to know more about the marine environment in the past. For example, scientists would be able to tell from the shell of a quahog, how warm the seas were two centuries ago! The quahogs are the only surviving species of a family of similar claims that had lived during the Dinosaur era!

The ocean quahog (Arctica is landica) lives in the North Atlantic Ocean, buried in sandy sea beds. It feeds on the organic matter it gets by filtering water using its siphon. Interestingly, their feeding activity seems to depend on how much light is available! Thus, in the northern-most regions where they are found, they mostly feed during eight months of the year. During the remaining months, they feed for only a few days.

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