Category: Geography Notes PPT

The detailed study of different types of landforms and their attributes is known as topography. The term is also present in biology and it falls under the chapter of microscopy. However, the topography biology definition has similarities with the geographic one as it means the study of the physical properties of an object. 

Here, we will discuss geographical topography. The ways of handling the topographic maps are discussed here. Moreover, you can define topography easily as you know the process of using it to solve different problems related to it. As a school student of any education board, you would have to study topography along with geography in the secondary and higher-secondary standards.    

What is Topography Meaning in Geography?

Topography in geography deals with the study of the surface of the earth or other celestial bodies. The main tool necessary for the study of topography is a toposheet. Toposheets are mainly available in parts divided concerning the area. 

Every minute detail of the land is present on the toposheet. While observing a topographic map you can observe the natural features along with the roads, drainage, buildings, and water bodies. It also shows the altitude of the place. However, these are the topography examples that are denoted in multiple toposheets. 

To theoretically denote a particular location you need to write the coordinates of the place. All toposheets contain the coordinates. You can find the gridlines forming the squares. These are topographic latitudes and longitudes. 

Procedures of Topographic Survey

There are two ways by which you can carry out topographic surveys on a toposheet. They are direct and indirect surveys. These are the techniques to gather information about a particular place. All the information is later used to create an area-wise toposheet for documentation. The details of the survey techniques are as follows:

Indirect Survey

Indirect survey in topography means gaining data with the help of satellite images, images taken from the flight, or radar images. Scientists studying topography prefer indirect surveys for their cost-effectiveness. Nowadays, indirect surveys take place with the help of remote sensing and it saves a lot of time and physical effort for the scientists. Usage of sonar to take note of the ocean floor conditions also falls under the indirect survey. 

Direct Survey 

The direct survey in topography is trickier than the indirect survey and it is time-consuming.  The instruments needed for the direct survey are theodolites, clinometers, and levels. It is done to survey landscapes. Concerning the studies, both direct and indirect topographic surveys are covered at the college levels. However, a few advanced educational boards make the students study the basics at the higher-secondary levels. 

Importance of Topography

Topography is important for many reasons and you should try to understand it while studying it. At school levels, basic topography can help you to score outstanding marks. The study of topography is important as it helps people of different fields to understand the condition of the land and take actions in a written way. 

Topography and Agriculture

Right topography can help agricultural experts to take the right track in conserving the soil. A continuous study of an area of land topographically can help scientists to understand the condition of the soil. Moreover, they can understand if soil conservation is needed or not.

If the scientists can gather authentic information about a piece of land with the help of topography, the right conservation techniques can be applied to ensure proper conservation of soil. Conditions like soil erosion can be minimized to a large extent. 

Topography and Weather

The weather office relies on the topographic outcomes mostly when it comes to giving the forecast. Topography helps the weather officials to understand the altitude and land condition and say about the wound gusts, storms, etc. 

Topography and Engineering

Civil engineers mostly need toposheets to examine the land surface of a specific construction site.

At times they also note down the 4 or 56 figure coordinates of a site. 

Topography in Army Use

The army of the country uses the topographic map to study a place. It helps them to locate all minute details of a place within an area.

Solved Examples

Q1.  What is the Information Present on the Margins of the Toposheet also called?

Answer: The other name for the marginal information of a topographic map is known as the primary information. It is called so as an individual can get access to all necessary information about the map at the margin. 

Q2. What should be the Direction at Your Left if you are Facing the rising Sun?

Answer: If you are facing the rising sun, you are facing east and the direction at your next should be north. You can always find north demarcation on a map or a toposheet. 

The abyssal zone is defined as the portion of the ocean which is deeper than about 2,000 m (that is 6,600 feet). This zone is shallower than about 6,000 m (which is 20,000 feet). The zone is defined mainly by the extremely uniform environmental conditions, which are being reflected as distinct life forms which belong to it. The upper boundary that lies between the abyssal zone and the overlying bathyal zone is the depth where the water temperature drops to 4° C (39° F). While this depth varies between 1,000 to 3,000 m. The waters that are deeper than 6,000 m are being treated separately by ecologists.

Abyssal Zone

The abyssal zone which is also called the abyssopelagic zone is the layer of the pelagic zone of the ocean. “Abyss” is a term derived from a Greek word, which means bottomless. At depths of 3,000 to 6,000 meters (which is approximately 9,800 to 19,700 ft), this zone remains in acute darkness. This zone covers around 83% of the total area of the ocean and covers 6l0% of the Earth’s surface. 

The abyssal realm is the largest environment in the Earth’s life, covering 300,000,000 square km (that is 115,000,000 square miles). Almost 60 percent of the global surface is covered by the zone and about 83 percent of the area of the oceans and seas.

At the air-sea interface, the waters of the Abyssal zone originate. The air-sea interface is in the polar regions, specifically in the Antarctic zone. For the cold climate of the Antarctic, sea-ice and residual cold brine get produced. Further for the high density in this region, the brine sinks and it slowly flows along the bottom towards the Equatorial region. Abyssal salinities range between 34.6 and 35.0 parts per thousand, while the temperature ranges mostly between 0° and 4° C (that is approximately 32° and 39° F). The Pressure system increases by about one atmosphere (which is approximately 14.7 pounds per square inch at sea level) with each 10-meter increment in the level of depth. Thereby, the abyssal pressures range between 200 and 600 atmospheres. The pressure in this zone presents fewer problems for the abyssal animals, however, because the pressures within their bodies are the same as those which are outside them.

Abyssal Zone Temperature

Majorly, the abyssal zone has a temperature ranging from 2 to 3 °C (which is 36 to 37 °F). As in the abyssal zone, there is no light, there are no plants growing in this zone, thus no oxygen is being produced. Oxygen minutely only comes from the ice that had melted long ago from the polar regions. The water on the seafloor of this zone is actually devoid of any oxygen content. This lack of oxygen results in a death trap for the organisms who are unable to quickly return to the oxygen-enriched water above. While, this region contains a much higher concentration of nutrient salts, like nitrogen, silica, and phosphorus, this happens for the large amount of dead organic material which seeps down from the above ocean zones and then decomposes in this zone. The water pressure present can reach up to 76 megapascals.

Abyssal Zone Location

This Abyssal Zone is one of the many benthic zones which is being highlighted in order to describe the deep oceans. This zone is found at the depth of around 2,000 to 6,000 meters (which is 6,560 to 19,680 feet) and it stays in perpetual darkness.

How Far Down is the Abyssal Zone?

The Abyssopelagic Zone or the abyssal zone extends from 13,100 feet (which is 4,000 meters) to 19,700 feet (that is 6,000 meters). The zone is characterized as the pitch-black bottom layer of the ocean. The name ‘abyss’ particularly comes from a Greek word that means “no bottom” or “bottomless” as previously it was wondered that the sea was bottomless.

Fun Facts about Abyssal Zone

• The concentrations of nutrient salts present in this zone are very much higher than in other zones. The nutrient salts – nitrogen, phosphorus, and silica present in this zone acts as a reservoir for the salts from the decomposed biological materials which settle downward from upper zones. Also, the lack of sunlight in this zone prevents photosynthesis thereby these nutrients are not being used as such. 

• The abyssal realm has a very calm zone which is being far removed from the storms which agitate in the ocean at the air-sea interface. The low energies are being reflected in the character of the abyssal sediments. 

• Abyssal sediment in the waters is shallower than 4,000 m in equatorial to temperate regions includes primarily the calcareous shells of zooplankton and of phytoplankton like coccolithophores. Below the 4,000 m, calcium carbonate tends to dissolve the principal sediment which are constituents which are brown clays and the siliceous remains of the radiolarian zooplankton like the phytoplankton as the diatoms.

• Abyssal fauna, is very sparse and there are relatively few species, among which includes representatives of all major marine invertebrate phyla and several other kinds of fish, all these are adapted to an environment that is being marked by no diurnal or by no seasonal changes, for high pressures, darkness, and calmer water, and softer sediment featured bottoms. These animals tend to be grey or black in colour, delicately they are being structured, and they have un-streamlined body structure. Some of these forms have long legs. Animals attached to the bottom have stalks which enables them to rise above the water layer which is nearest the bottom, where the oxygen is scarce. The abyssal crustaceans and the fish may be blind. With the increasing depth, the carnivores and the scavengers become less abundant than the animals who are fed on mud and by suspended matter. The abyssal animals are believed to reproduce at a slower rate.

You must have heard the news of spreading smog in Northern India in the dry winter season whereas also similar news in China when the formation of smog or air pollution can be seen that leads to a reduction in the visibility, affects the transportation system and various diseases as well. This happens because of the special phenomenon that we came to know about in the 1990s and has become a serious issue these days. In this article, we will be talking about this phenomenon which occurs every year and creates various problems including loss of the GDP of the countries on one side and various deaths on the other side. This topic will be helpful for you whenever you are studying the clouds as well as air pollution in Geography or Environmental studies.

Introduction

A cloud is an aerosol that is made of water drops and ice crystals floating in the sky. There are many kinds of clouds that can be formed in the atmosphere as per the geographical conditions. Clouds are an important part of the earth’s atmosphere which leads to various forms of precipitation especially rainfall. If we talk about a special kind of clouds i.e.. Atmospheric Brown Clouds ( ABCs ), are those clouds that lead to air pollution and consist of aerosols that lead to the absorption as well as scattering the sunlight coming from the Sun. These brown clouds lead to imposing serious impacts not only on the climate but also on human life as well. The first time, this phenomenon was detected in the late 1990s during Indian Ocean Experiment. Let’s study comprehensively the phenomena of Asian Brown Clouds below.

About Asian Brown Cloud

It is a form of atmospheric haze that contains particles of black carbon, soot, fly ash, as well as numerous toxic chemicals. These are caused by emissions from the burning of fossil fuels and biomass which is spread across the region. It is a regional size layer of toxic air pollution known as the “Asian Brown Cloud.” It appears every year between the months of December and March, the time when there is little to no rain to wash pollutants out of the air. It causes health issues all over the region. All the Asian brown clouds consist of emissions from burning fossil fuels such as coal or petroleum or natural gas products and biomass ( wood, crop stubble). 

This so-called “Asian Brown Cloud” is also known as the ” Indian Ocean Brown Cloud.”  which is an extensive layer of toxic air pollution. It materializes annually over parts of the northern Indian Ocean, the Indian subcontinent, Bangladesh and China. This term was first used in reports submitted by the UN Indian Ocean Experiment (INDOEX) in 1999. There was research established to measure the atmospheric movements of air pollution from southeast Asia into the Indian Ocean. During this experiment, air pollutants are measured by satellites and surface monitoring stations. They saw a vast carbonaceous aerosol haze over most of South Asia and the northern Indian ocean. While local brown clouds polluted the atmosphere of the urban areas for half a century but the scientists did have any clue about it. And they also do not have any idea about their large scale effects on the temperature of the atmosphere or the issues which are caused by it.

Causes

There are some causes that lead to the occurrence of this atmospheric haze which is mentioned below:

• All atmospheric brown clouds are made because of the emissions of burning fossil fuels such as coal or petroleum, natural gas and biomass.

• Due to ABC(Atmospheric Brown Clouds) Sulphur dioxide emissions have increased 600-700 per cent in India and 1000 per cent in China. This happened at the time of 1950.

• At the same time, soot emissions jumped 300 per cent in India while in China, black carbon emissions rose 500 per cent.

• Black carbon which is released by incomplete burning of vehicle diesel or fuel is the major constituent of the Asian Brown Cloud and an important contributor to climate change.

• Nitrogen oxide and Sulphur dioxide emissions from burning coal and other fossil fuels are other important constituents of Asian brown clouds.

• Air pollution is caused in India by numerous environmentally damaging activities. In Delhi, it is caused by a mixture of coal combustion from coal-fired power plants.

Composition of Atmospheric Brown Clouds

The Asian brown clouds consist of two types of climate pollutants – tiny particles and gases.  The particles are known as “particular matter”. In this, several inorganic particles, carbonaceous species, soot, fly ash and mineral dust are included. Among them, black carbon is one of the most significant and damaging components.

Gases that make clouds include SO_x(Sulphur oxides), NO_x((nitrogen oxides), VOCs (Volatile organic compounds), CO(Carbon monoxide) and CH4 (Methane). These all are the components of ground-level ozone(O3) and other secondary pollutants. The brown colour of clouds are occurring because of the absorption and scattering of sunlight by soil dust particles, black carbon, fly ash and nitrogen oxides.

Impacts

Asian Brown Clouds cause a greater impact not only on the climate and weather activities of the region but also on Humans as well. Let’s have a look at the impacts of these clouds by dividing them into two major categories:

Impacts on Climate

• Asian Brown Clouds usually consist of black carbon as well as organic carbon which absorbs incoming sunlight and the heat rising from the surface of the Earth and this activity leads to the warmness of the atmosphere and double the heat in the troposphere. This also leads to imposing impacts on the rainfall and water cycle.

• If we talk about aerosols, the carbon aerosols prevent the sunlight coming from the sun from getting through the surface of the Earth whereas other aerosols lead to send back the sunlight into space. Combinedly, they lead to a phenomenon called dimming. Reduction in the sunlight leads to the cooling effect of the surface of the Earth. 

• It also affects cloud formation which leads to rainfall. Polluted air is said to have more water-soluble particles than unpolluted air and more particles lead to more droplets which leads to an increase in the albedo or reflectiveness of the clouds. They will reflect more sunlight into the space that will cause more cooling effect here on the Earth but if this cooling effect does not happen then the Indian Ocean will become very hot. Thus, in this case, it represents both positive and negative impacts.

• The formation of these Asian brown clouds also leads to less rainfall in the region. When the surface temperature reduces because less sunlight reaches the surface and this lower temperature leads to less evaporation which in turn leads to less formation of clouds that will lead to less precipitation. This less rainfall causes great impacts on agriculture and irrigation activities.

• These clouds lead to impart the regions in various other forms such as in eastern China, a southward shift of summer monsoon occurs and changes in rainfall as well. These clouds also lead to a reduction in summer monsoon clouds in India as well. 

• On the other hand, it leads to an increase in rainfall in some parts of Australia such as Kimberly and other top-end regions. The emergence of pollutants in India also gets shifted towards the Hindukush mountains which increases the greenhouse effect there.

• These clouds also cause haze, fog or smog in the Indo Gangetic region in the dry season which leads to air pollution and reduces visibility as well. It also causes impacts on crops and tourists. 

• Because of these clouds, a various number of cyclones have also been seen in the Arabian sea where the occurrence of this cyclonic activity is very less. Not only this, but these clouds also lead to the melting of ice in the Arctic. According to NASA’s GISS, ⅓ of black carbon here comes from South Asia which leads to the melting of ice.

Impact on Humans

• These clouds can lead to having a great impact on climate and rainfall thus can impact agricultural activities. These impacts can be complex and depend upon the type of crops. For example, according to the studies in 1985-1998, due to air pollution because of these clouds, rice production in India declined by 6.2 million metric tons. According to another study, crop yields can be declined by 20 – 40% in polluted areas.

• Health effects are also recognised by the United Nations because of these Asian Brown Clouds. PM 2.5 can lead to many diseases such as heart disease, respiratory problems, etc. Ozone can lead to asthma attacks and also reduce lung function. Besides these, cancer-causing agents are also present in these clouds. Around 4,00,000 deaths due to indoor air pollution in India and China whereas 5,00,000 deaths per year due to outdoor air pollution have been seen because of Asian brown clouds. 

• Besides these, Asian brown clouds can cause economic losses. For example, it causes economic losses of about 2.2% of GDP in India whereas 3.6% of GDP in China. It not only affects the agricultural sector of the economy but also other sectors as well.

Impact of Indian Monsoon on Asian Brown Cloud

Asian brown clouds usually occur from December to March and, after that, these clouds with the arrival of the monsoon washes away. When the monsoon comes, it leads to the presence of rainy months which fulfils the water demand and is helpful for production as well. In these months, it helps in cleansing the air pollution from the atmosphere including the Asian brown clouds. But, because of this activity, some of the pollutants moved to the upper troposphere by the warm air which then spread in the whole world. Actually, all the pollutants are transported above the monsoon clouds into anticyclones from where they are being distributed in the whole world. Besides these, around 10% of Sulphur dioxide emissions also reach up to the stratosphere which leads to an impact on the ozone layer. Therefore, the Indian Monsoon not only helps in removing the air pollution but on the other hand also helps in spreading the air pollution in other parts of the world.

Additional Information

• The presence of these clouds is not local but regional. For example, the presence of such toxic brown clouds ie. Smog can be seen over Mexico City, Los Angeles for decades. If we talk about ABCs, they not only cover the cities but the whole region. Sometimes the whole continent or ocean might be covered. For example, it can be seen in India, China, Bangladesh, and the Bay of Bengal.

• The brown clouds do not only occur in Asia but other parts of the world as well such as in North America, South America, Africa and Europe. The main hotspots where ABCs are found are East Asia and South Asia including Eastern China, India, Bangladesh, Pakistan and Southeast Asia which includes Cambodia, Thailand, Vietnam, and Indonesia whereas, in Africa, they can be found in Angola, Zimbabwe and Zambia and also in the Amazon basin in South America.

Conclusion

To conclude, Asian Brown Clouds are a form of smog or haze that is caused by the combination of emissions from power plants, burning of fossil fuels, natural gas products and biomass. It caused health problems all over the region. It is also known as the ” Indian Ocean Brown Cloud” which is an extensive layer of toxic air pollution. These kinds of brown clouds not only occur in the Asian regions but also in other parts of the world which affects the climatic and geographical locations over there and also cause various economic and health problems as well. Required steps or measures need to be taken at regional and international levels to control the emissions and air pollution which leads to the occurrence of these brown clouds.

Bituminous coal is actually the most copious rank of coal found in the United States, and it accounted for approximately 48% of U.S total coal production in 2019. In the United States, it is aged between 100 million and 300 million years old. Bituminous coal is used for producing electricity and is a significant fuel and raw material for generating coking coal. It is also used as a raw agent in the iron and steel industry.

Percentage of Carbon in Bituminous Coal

The Bituminous coal comprises 45%–86% of carbon. Coal rock is actually composed of almost pure carbon. The coal in different deposits consists of different configurations, thus, coal is divided in different categories. After Anthracite, Bituminous coal is the second highest quality of coal and the most copious type. Generally, it is derived from fairly old coal deposits (about 300 million years) and exposes a carbon content which varies from 76-86%. The energy density of this coal is comparatively high (27 MJ/kg), thus, disperse a substantial amount of energy when burned.

Heating Value of Bituminous Coal

Bituminous coal renders about 10,500 to 15,000 BTU per pound when mined.

Prosperities of Bituminous Coal

• Bituminous coal has moisture content up to 17%.

• Approximately 0.5 to 2% of the weight of bituminous coal is nitrogen.

• Its fixed carbon content ranges up to 85%, with ash content up to 12% in weight.

• The calorific value of bituminous coal A is 8 – 10% about 6,300 – 7,000 kcal/kg while that of medium volatile bituminous has 7,000 – 8,000 kcal/kg.

• Bituminous coal can be further divided by the level of volatile matter it consists of, like high-volatile A, B, and C, medium-volatile, and low-volatile.

• Volatile matter takes into account any material that is free from the coal at high temperatures.

• In the context of coal, the volatile matter may include sulfur and hydrocarbons.

What is Sub Bituminous Coal?

Subbituminous coal essentially comprises 35%–45% carbon, and comparatively has a lower heating value than bituminous coal. Most sub bituminous coal in the U.S are at least 100 million years old. Around 44% of the total coal production of the United States in 2019 was subbituminous while the remainder was yielded in Alaska, Colorado and New Mexico.

Bituminous Coal Uses

High carbon content and low moisture of this specific coal type makes it ideal in the production use of steel and cement, as well as in coke production and electricity generation and coke production.

Types and Uses of Bituminous Coal Uses

Bituminous Coal is divided into 2 type’s i.e.

1. Thermal Coal

2. Metallurgical Coal

Thermal Coal: also referred to as steaming coal, it is deployed to power plants which produce steam for electricity and industrial uses. Trains that operate on steam engines often are fueled with “bituminous coal,”.

Metallurgical Coal: also sometimes called coking coal, is used in the making of coke. This type of coke is a source of carbon necessary for making steel and iron.

Environmental Concerns Associated With Bituminous Coal

• Bituminous coal ignites fire easily and can thus yield immoderate smoke and soot – if burned improperly.

• The high sulfur of bituminous contributes to acid rain.

• Consisting of the mineral pyrite, which caters as a host for impurities such as arsenic and mercury, it releases pollution in the air.

• When burned, bituminous coal releases hazardous emissions like hydrogen fluoride (HF), hydrogen chloride (HCl), and polycyclic aromatic hydrocarbons (PAHs).

• Partial combustion results in higher levels of PAHs that are carcinogenic.

Bituminous Coal Facts

• Bituminous coal ranks 2nd in carbon and heat content in comparison to other types of coal

• Earlier in the 20th century, bituminous coal mining was a tremendously dangerous task, taking away the lives of an average of 1,700 coal miners’ annually. About 2,500 workers per year were left permanently disabled as an outcome of coal mining mishap.

• Little particles of bituminous coal waste left over after preparation of commercial-grade coal is known as “coal fines.”

• Coal Fines are very light weighted, dusty, and difficult to manage, and traditionally were stored with water in alluvium impoundments to prevent them from blowing away.

• Breakthrough technologies have been developed to recoup coal fines. One technique employs a centrifuge to isolate the coal particles from the alluvium water. Other techniques bind the fines into briquettes which contain low moisture content, making them apt for fuel use.

• Bituminous coal has been generated in at least 19 states in 2019, but five states reckoned around 75% of total bituminous production: West Virginia accounted for 27.5%, Pennsylvania (14.0%), Illinois (13.5%), Kentucky (10.6%), and Indiana (9.3%).

Do you want to know about the various perspectives of chlorite minerals? I guess your answer is a big yes. So in this section, we will talk about chlorite meaning which is basically a sheet group consisting of several silicates. Can’t believe it? Don’t worry. Let’s talk about it some more.

         

        

Introduction to Chlorite Mineral

The name chlorite is basically a part of a Greek word which is chloros. The meaning of this Greek word is none other than green which is a complete reference to the color of the chlorite minerals.

Are you confused with Chlorine? Don’t be confused. Because the chlorite mineral can’t contain any chlorine. It is just the name of a Greek root.

Chlorite Properties

In this section, we will generally discuss the basic physical properties of chlorites.

A chlorite is a group of phyllosilicate sheets of minerals such as Magnesium, Iron, Nickel, Calcium as well as Manganese. It can generally be found during the metamorphism phases. Apart from that, Zinc and Lithium also have a special role.

The maximum number of chlorite minerals are coming is a greenish color. It is because of its foliated emergence as well as it has perfect cleavages of perfect 001. Chlorites ate very oily in nature to feel soapy.

The chlorite minerals have a refractive index of almost 1.57 to 1.67. It has a lamellar fracture pattern.

Most chlorites are green but it has a foliate presence. So that everyone who touches chlorite can feel soapy. On the contrary, the several chemical compositions make chlorite with an individual hardness of 2 to 2.5 according to the Mohs scale. It has a different specific gravity of 2.6 to 3.3 which is completely different from any other minerals.

Aren’t Chlorite Properties Interesting?

One can easily recognize a group of chlorite. However, the identification of a specific name can be difficult in some way. In that case, a detailed optical and chemical report, as well as an X-ray analysis, is mandatory for positive dissemination.

The saddest part is that the individual chlorites are less known to people.

Collection of Minerals

Here we will talk about the collection method of minerals.

The best way is to collect specimens. The next step is to do a clear study with the collective specimens or samples. You have to observe the sample as well as their properties.

Formation of Chlorite

The chlorites typically form in the rocky environment. Here heat alters with the minerals along with pressure. There is an extreme change in the chemical activities of the minerals. Sounds interesting right? Apart from that, chlorites form in sedimentary rocks also but those sedimentary rocks should be clay-rich. Even those chlorite minerals bury in those deep sedimentary rock basins. Therefore these minerals are generally subjected to regional metamorphism. Can’t believe it? Let’s talk about more.

Regional metamorphism of chlorite minerals can take place only in the convergent boundaries of plates. These chlorites are associated with Muscovite, Cordierite, Andalusite as well as Biotite. Garnet along with Staurolite has specific roles to play.

On the contrary, it is found that the metamorphic rocks are very rich in chlorite which includes chlorite schist and phyllite as well. 

Not only in rocks, another suitable environment for the formation of chlorite minerals none other than in the oceanic crust. When these crusts are descending to the subduction zones, the chlorite minerals can form. However, chlorite alters with several other minerals such as micas, amphiboles along pyroxenes.

Can you believe that chlorite can form in various conditions?

The chlorite minerals also form during the metasomatic environment as well as the hydrothermal processing. These minerals occur in the fracture zones, in the igneous rocks, and the solution cavities as well.

Who knew that individual chlorite can have so many formations?

The movement of the Earth’s continents relative to one other, causing them to seem to drift together over the sea bed, is characterised as the Theory of Continental Drift. Although Alfred Wegener was able to establish a plausible hypothesis with data and precisely articulate the idea, it should be remembered that Wegener was not alone in his thinking. Between 1889 and 1909, for example, Roberto Mantovani theorised that all continents had previously been linked in a “supercontinent,” and even created an expanding earth idea.

Continental Drift Theory of Wegener

In 1910, Alfred Wegener became interested in the notion of continental drift after noticing how Earth’s continents resembled jigsaw puzzle pieces. He observed how the coast of South America perfectly aligned with the coast of Northwest Africa. Wegener’s true love for the subject came to light in 1911, when he came across multiple scientific records documenting fossils of similar plants and animals discovered on different sides of the Atlantic. 

In the 1920s, Alfred Wegener proposed the continental drift theory. According to Continental Drift Theory, there was once a single large continent known as Pangaea, which was surrounded by a single large ocean known as Panthalassa. Pangaea was separated into two large landmasses by a sea named Tethys: Laurentia (Laurasia) to the north and Gondwanaland to the south of Tethys. Drift began some 200 million years ago (Mesozoic Era, Triassic Period, Late Triassic Epoch), with continents breaking up and drifting apart.

The drift, according to Wegener, was in two directions: equatorwards owing to the interplay of gravity, pole-fleeing force (produced by the earth’s rotation) and buoyancy (ship floats in water due to buoyant force given by water), and westwards due to tidal currents induced by the earth’s motion (earth rotates from west to east, so tidal currents act from east to west, according to Wegener). Tidal force (the gravitational attraction of the moon and, to a lesser extent, the sun) was also hypothesised by Wegener to have a significant effect. 

The polar-fleeing force is related to the earth’s rotation. The Earth is not a perfect spherical; it has an equatorial bulge. This bulge is caused by the earth’s rotation (greater centrifugal force at the equator). As we go from the poles to the equator, the centrifugal force rises. According to Wegener, the rise in centrifugal force has resulted in pole fleeing. Tidal force is caused by the moon’s and sun’s attraction, which causes tides to form in marine seas. These pressures, according to Wegener, would become effective if applied over several million years, and the drift is ongoing.

Evidences and Drawbacks of Continental Drift Theory

Aside from the way the continents fit together, Wegener and his allies gathered a substantial amount of data to support the continental drift idea. For example, similar rocks of the same sort and age can be found on both sides of the Atlantic. Wegener stated that the rocks formed side by side and that the earth has since separated. On opposite sides of the Atlantic Ocean, mountain ranges with comparable rock types, structures, and ages can be found.

Mountain ranges in eastern Greenland, Ireland, the United Kingdom, and Norway, for example, are similar to those in the eastern United States and Canada’s Appalachians. Wegener came to the conclusion that they began as a single mountain range that was divided when the continents drifted apart. Ancient fossils of the same extinct plant and animal species have been discovered in rocks of the same age but on continents that are currently widely distant. Wegener argued that the species had coexisted, but that the lands had separated after they died and were petrified.

He hypothesised that the creatures could not have travelled across the oceans. The fossils of the seed fern Glossopteris, for example, were too heavy to be transported thus far by wind. The swimming reptile Mesosaurus could only swim in freshwater. Cynognathus and Lystrosaurus were terrestrial reptiles that couldn’t swim. Grooves and rock deposits left by past glaciers may still be observed today on several continents around the equator. This would imply that the glaciers developed in the midst of the ocean and/or covered the majority of the Earth. Glaciers now develop exclusively on land and near the poles.

Wegener hypothesised that glaciers were focused over the southern land mass around the South Pole, and that the continents shifted to their current locations later. Although coral reefs and coal-forming wetlands are located in tropical and subtropical habitats, ancient coal seams and coral reefs are discovered in regions that are far too cold now. Wegener hypothesised that these organisms existed in warm temperature zones and that the fossils and coal had later moved to other sites on the continents.

Despite Wegener’s compelling data, most geologists at the time dismissed his theory of continental drift. Scientists contended that there was no explanation for how solid continents could smash through solid oceanic crust. Wegener’s theory was practically forgotten until technology developments provided further proof that the continents migrated and provided scientists with the means to devise a mechanism for Wegener’s floating continents.

Drawbacks of the Theory

• Wegener did not explain why the drift started only in the Mesozoic era and not earlier. 

• Oceans are not taken into account in the hypothesis. 

• Proofs rely significantly on generalizable assumptions.

• Buoyancy, tidal currents, and gravity forces are insufficient to move continents. 

• Modern theories (Plate Tectonics) acknowledge the existence of Pangaea and comparable land masses but explain the reasons for drift in a fundamentally different way.

Despite being factually incorrect on several counts, Wegener’s hypothesis represents a key milestone in the study of tectonics, laying a solid framework for future hypotheses such as seafloor spreading and plate tectonics.