Index
ATMOSPHERE... 1
Origin of the atmosphere ... 1
Main layers ... 1
Importance of atmosphere ... 3
Two very important global environmental problems... 4
Climate change ... 4
The Ozone Hole... 4
Atmospheric pollutants ... 5
Global Greenhouse effect emissions ... 5
Local atmospheric pollutants ... 6
HYDROSPHERE ... 7
Water scarcity ... 7
Water Pollution ... 7
The water cycle ... 7
Importance of water for life ... 8
GEOSPHERE ... 9
The Earth: a layered body ... 9
Why the interior of the earth is divided into layers? ... 9
Materials on the Earth’s crust ... 10
Minerals ... 10
Rocks ... 10
Examples of observable features in rocks ... 11
Common uses of rocks and minerals ... 11
Atmosphere
The atmosphere of Earth is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night.
By volume, dry air contains 78% nitrogen, 21% oxygen, 0.9% argon, 0.04% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapour.
Origin of the atmosphere
Earth is believed to have formed about 4,6 billion years ago. In the first 500 million years a dense atmosphere emerged from the vapor and gases that were expelled during degassing of the planet's interior. The hydrosphere was formed 4 billion years ago from the condensation of water vapor, resulting in oceans of water. The most important feature of the ancient environment was the absence of free oxygen.
At one point, about 2,5 billion years ago, early aquatic organisms called blue-green algae began using energy from the Sun to split molecules of H2O and CO2 and recombine them into organic compounds and molecular oxygen (O2). This solar energy conversion process is known as photosynthesis. Oxygen started to accumulate in the atmosphere.
High in the atmosphere, some oxygen (O2) molecules absorbed energy from the Sun's ultraviolet (UV) rays and split to form single oxygen atoms. These atoms combine with remaining oxygen (O2) to form ozone (O3) molecules, which are very effective at absorbing UV rays. The thin layer of ozone that surrounds Earth acts as a shield, protecting the planet from irradiation by UV light.
The amount of ozone required to shield Earth from biologically lethal UV radiation is believed to have been in existence 600 million years ago. Prior to this period, life was restricted to the ocean. The presence of ozone enabled organisms to develop and live on the land. Ozone played a significant role in the evolution of life on Earth, and allows life as we presently know it to exist.
Regarding the origin of N2, it originates from regions of the Earth where plates are converging, in volcanoes and is produced by (denitrifying) bacteria that live in the bottom of the oceans1. Nitrogen is fairly non-reactive with most materials that make up the solid part of Earth, and it is very stable in the presence of solar radiation in the atmosphere.
Life on Earth (Ocean + Land) and precipitation have taken CO2 out of the atmosphere. Earth is a distinctly unique planet because it undergoes hydrologic, geologic, and biological processes that take CO2 out of the atmosphere.
Main layers
Air content and atmospheric pressure vary at different layers, that can be distinguished based on characteristics such as temperature and composition. Air suitable for use in photosynthesis by terrestrial plants and breathing of terrestrial animals is found only in Earth's troposphere, the closest layer to the Earth’s surface. The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space.
In general, air pressure and density decrease with altitude in the atmosphere. However, temperature has a more complicated profile with altitude, and may remain relatively constant or even increase with altitude in some regions. The temperature behavior provides a useful metric to distinguish atmospheric layers. In this way, Earth's atmosphere can be divided into five primary layers.
The exosphere is the upper limit of the atmosphere. It extends from the exobase, which is located at the top of the thermosphere at an altitude of about 700 km above sea level, to about 10,000 km where it merges into the solar wind. The atoms and molecules are so far apart that they can travel hundreds of kilometers without colliding with one another. Thus, the exosphere no longer behaves like a gas, and the particles constantly escape into space. The exosphere contains most of the satellites orbiting Earth.
The thermosphere is the second-highest layer of Earth's atmosphere. It extends from the mesopause (which separates it from the mesosphere) at an altitude of about 80 km up to the thermopause (aka exobase) at an altitude range of 500–1000 km. The height of the thermopause varies considerably due to changes in solar activity. The lower part of the thermosphere, from 80 to 550 kilometres above Earth's
surface, contains the ionosphere2 (a region that is ionised by solar radiation). The temperature of the thermosphere gradually increases with height3. This layer is completely cloudless and free of water vapor. However non-hydrometeorological phenomena such as the aurora borealis and aurora australis are occasionally seen in the thermosphere. The International Space Station orbits in this layer, between 320 and 380 km.
The mesosphere is the third highest layer of Earth's atmosphere, occupying the region above the stratosphere and below the thermosphere. It extends from the stratopause at an altitude of about 50 km to the mesopause at 80–85 km above sea level. Temperatures drop with increasing altitude to the mesopause that marks the top of this middle layer of the atmosphere. It is the coldest place on Earth and has an average temperature around -85 °C4. The mesosphere is also the layer where most meteors burn up upon atmospheric entrance.
2The ionosphere forms the inner edge of the magnetosphere. It has practical importance because it influences, for example, radio propagation on Earth
3 Unlike the stratosphere beneath it, wherein a temperature inversion is due to the absorption of radiation by ozone, the inversion in the thermosphere occurs due to the extremely low density of its molecules. The temperature of this layer can rise as high as 1500 °C, though the gas molecules are so far apart that its temperature in the usual sense is not very meaningful. Although the thermosphere has a high proportion of molecules with high energy, it would not feel hot to a human in direct contact, because its density is too low to conduct a significant amount of energy to or from the skin.
The stratosphere is the second-lowest layer of Earth's atmosphere. It lies above the troposphere and is separated from it by the tropopause. This layer extends from the top of the troposphere at roughly 12 km above Earth's surface to the stratopause at an altitude of about 50 to 55 km. The atmospheric pressure at the top of the stratosphere is roughly 1/1000 the pressure at sea level. It contains the ozone layer, which is the part of Earth's atmosphere that contains relatively high concentrations of that gas. The stratosphere defines a layer in which temperatures rise with increasing altitude. This rise in temperature is caused by the absorption of ultraviolet radiation (UV) radiation from the Sun by the ozone layer, which restricts turbulence and mixing. Although the temperature may be -60 °C at the tropopause, the top of the stratosphere is much warmer, and may be near 0 °C. The stratospheric temperature profile creates very stable atmospheric conditions, so the stratosphere lacks the weather-producing air turbulence that is so prevalent in the troposphere. Consequently, the stratosphere is almost completely free of clouds and other forms of weather. This is the highest layer that can be accessed by jet-powered aircraft.
The troposphere is the lowest layer of Earth's atmosphere. It extends from Earth's surface to an average height of about 12 km, although this altitude actually varies from about 9 km at the poles to 17 km at the equator, with some variation due to weather. The troposphere is bounded above by the tropopause, a boundary marked in most places by a temperature inversion. The temperature usually declines with increasing altitude in the troposphere because the troposphere is mostly heated through energy transfer from the surface. Thus, the lowest part of the troposphere (i.e. Earth's surface) is typically the warmest section of the troposphere. The troposphere contains roughly 80% of the mass of Earth's atmosphere. Nearly all atmospheric water vapor or moisture is found in the troposphere, so it is the layer where Earth's weather takes place. It has basically all the weather-associated cloud genus types generated by active wind circulation. Most conventional aviation activity takes place in the troposphere, and it is the only layer that can be accessed by non jet-powered aircraft.
Importance of atmosphere
The earth is the only known planet, on which life exists. The present condition and properties of earth’s atmosphere are one of the main reasons for earth to support life. The atmosphere is special because:
It contains life-sustaining oxygen in large quantities. In fact, it took millions of years to reach the present condition. Along with its development, life came into existence and evolved.
When solar radiation passes through the atmosphere harmful ultraviolet radiation is “absorbed” by the ozone layer in the stratosphere. Ozone layer prevents about 95% of harmful ultra-violet radiation from reaching the earth’s surface.
Heated earth emits the energy in the form of infrared radiation during nightime and this radiation is absorbed by carbon dioxide, water and few other gases. This process results in “greenhouse effect” by which the atmosphere is kept warm during night, otherwise it will become so cool and intolerable for living organisms.
Nitrogen is converted into useful forms for life by certain micro organisms. Nitrogen is very important in the formation of amino acids, which are building blocks of proteins, and also in the formation of nucleotides, which are part of the genetic materials such as DNA.
Most living organism, including humans, need oxygen for respiration. Respiration is the process through which the chemical energy (food) is converted into usable form of energy by the living cells.
Carbon dioxide is emitted by all living organisms as an end product of respiration. This carbon dioxide, in turn is used by producer organisms (green plants and certain microorganisms) for the synthesis of food. This process is called, photosynthesis. It plays significant role in keeping the atmosphere at temperatures that permit life. The concentration of carbon dioxide, nowadays, is increasing due to human activities. Today, man burns large quantities of fossil fuels for various purposes. As a result, huge amounts of carbon dioxide are emitted into the atmosphere. Its ever increasing concentration has already resulted in climate change
Water vapor, though present in small quantities, plays a crucial role. It is responsible for cloud formation in the atmosphere and precipitation. Its concentration varies over time at a given place and at different places. It is an important component of the atmosphere in determining the weather of a place at a given time. Water vapor also absorbs outgoing radiation from earth and it has a crucial role in green house effect. Thus, both CO2 and H2O along with ozone (in troposphere), methane and N2O are called,
greenhouse gases. In addition, water present in clouds, can reflect and absorb the part of the incoming
Two very important global environmental problems
Climate changeOur Earth is warming. Earth's average temperature has risen by 0,8°C over the past century, and is projected to rise another 1,2 to 6.3°C over the next hundred years. Small changes in the average temperature of the planet can translate to large and potentially dangerous changes in climate and weather.
Many places have seen changes in rainfall, resulting in more floods, droughts, or intense rain, as well as more frequent and severe heat waves. The planet's oceans and glaciers have also experienced some big changes - oceans are warming and becoming more acidic, ice caps are melting, and sea levels are rising. As these and other changes become more pronounced in the coming decades, they will likely present challenges to our society and our environment.
Over the past century, human activities have released large amounts of carbon dioxide and other greenhouse gases into the atmosphere. The majority of greenhouse gases come from burning fossil fuels to produce energy, although deforestation, industrial processes, and some agricultural practices also emit gases into the atmosphere. Greenhouse gases act like a blanket around Earth, trapping energy in the atmosphere and causing it to warm. This phenomenon is called the greenhouse effect and is natural and necessary to support life on Earth. However, the buildup of greenhouse gases can change Earth's climate and result in dangerous effects to human health and welfare and to ecosystems.
Our lives are connected to the climate. Human societies have adapted to the relatively stable climate we have enjoyed since the last ice age which ended several thousand years ago. A warming climate will bring changes that can affect our water supplies, agriculture, power and transportation systems, the natural environment, and even our own health and safety. Although it's difficult to predict the exact impacts of climate change, what's clear is that the climate we are accustomed to it is no longer a reliable guide for what to expect in the future.
The Ozone Hole
First things first - what is ozone? Ozone is made of three oxygen atoms (O3). Ozone is constantly being formed in the earth's atmosphere by the action of the sun's ultraviolet radiation5 on oxygen molecules. Ultraviolet light splits the molecules apart by breaking the bonds between the atoms. A highly reactive free oxygen atom then collides with another oxygen molecule to form an ozone molecule. Because ozone is unstable, ultraviolet light quickly breaks it up, and the process begins again.
About 90% of the ozone in the earth's atmosphere lies in the region called the stratosphere between 16 and 48 kilometers above the earth's surface. Ozone forms a kind of layer in the stratosphere, where it is more concentrated than anywhere else. Ozone and oxygen molecules in the stratosphere absorb ultraviolet light from the Sun, providing a shield that prevents this radiation from passing to the earth's surface. While both oxygen and ozone together absorb 95 to 99.9% of the Sun's ultraviolet radiation, only ozone effectively absorbs the most energetic ultraviolet light, known as UV-C and UV-B, which causes biological damage. The protective role of the ozone layer in the upper atmosphere is so vital that scientists believe life on land probably would not have evolved - and could not exist today - without it.6
In the 1970s, people all over the world started realizing that the
5To understand how ozone is generated and the functions it serves in the earth's atmosphere, it is important to know
something about the electromagnetic spectrum — the energy emitted from the sun. Progressing from short wavelengths to long wavelengths, scientists have identified gamma rays, x-rays, ultraviolet radiation, visible light (between 400 and 700
nanometers), infrared radiation (heat), microwaves, and radio waves. Short wavelengths have more energy per photon than long wavelengths.
6In the troposphere, ozone is not wanted. Ozone is even more scarce in the troposphere than the stratosphere. But even in such small doses, this molecule can do a lot of damage in our respiratory tract. And just to confuse things even further, ozone in the troposphere is one of the greenhouse gases. So, in the troposphere, accelerated ozone levels deal us a double trouble -
ozone layer was getting thinner and that this was a bad thing. Many governments and businesses agreed that some chemicals, called chlorofluorocarbons (CFCs) are a reason we have a thinning ozone layer. CFCs are mostly in refrigerants and plastic products. They are used because they're inexpensive, they don't catch fire easily, and they don't usually poison living things. But the CFCs start eating away at the ozone layer once they get blown into the stratosphere.
The first international treaty to protect the ozone layer was signed in 1987. The Montreal Protocol on Substances That Deplete the Ozone Layer has been amended several times since then in response to new scientific information, and it has been ratified by 190 countries. Under it industrialized countries phased out production of several classes of ozone-depleting substances by 1996, and developing countries were to follow suit by 2010. The ozone layer is slowly recovering as governments work to control such pollution.
Atmospheric pollutants
Many forms of atmospheric pollution affect human health and the environment at levels from local to global. Global Greenhouse effect emissions
At the global scale, the key greenhouse gases emitted by human activities are:
Carbon dioxide (CO2) - Fossil fuel use is the primary source of CO2. CO2 can also be emitted from direct human-induced impacts on forestry and other land use, such as through deforestation, land clearing for agriculture, and degradation of soils. Likewise, land can also remove CO2 from the atmosphere through reforestation, improvement of soils, and other activities.
Methane (CH4) - Agricultural activities, waste management, energy use all contribute to CH4 emissions.
Nitrous oxide (N2O) - Agricultural activities, such as fertilizer use, are the primary source of N2O emissions.
Fluorinated gases (F-gases) - Industrial processes, refrigeration, and the use of a variety of consumer products contribute to emissions of F-gases, which include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).
Global greenhouse gas emissions can also be broken down by the economic activities that lead to their production.
Electricity and Heat Production (25% of 2010 global greenhouse gas emissions) - The burning of coal, natural gas, and oil for electricity and heat is the largest single source of global greenhouse gas emissions.
Agriculture, Forestry, and Other Land Use (24% of 2010 global greenhouse gas emissions) - Greenhouse gas emissions from this sector come mostly from agriculture (cultivation of crops and livestock) and deforestation
Transportation (14% of 2010 global greenhouse gas emissions) - Greenhouse gas emissions from this sector primarily involve fossil fuels burned for road, rail, air, and marine transportation. Almost all (95%) of the world's transportation energy comes from petroleum-based fuels, largely gasoline and diesel.
Local atmospheric pollutants
Major pollutants produced by human activity include:
SO2 - Coal and petroleum often contain sulfur compounds, and their combustion generates sulfur dioxide, which is a severe irritant of the eyes, mucous membranes and skin. When SO2 mixes with rainwater forms H2SO4, and thus acid rain.
Nitrogen oxides (NOx) - Nitrogen oxides, particularly nitrogen dioxide, are expelled from high temperature combustion mainly due to diesel cars. It irritates the respiratory tract
Carbon monoxide (CO) - CO is a colorless, odorless, toxic yet non-irritating gas. It is a product by incomplete combustion of diesel or gasoline. Vehicular exhaust is a major source of carbon monoxide.
Particulates, alternatively referred to as particulate matter (PM), atmospheric particulate matter, or fine particles, are tiny particles of solid or liquid suspended in a gas. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes generate significant amounts of aerosols. Increased levels of fine particles in the air are linked to health hazards such as heart disease, altered lung function and lung cancer.
Hydrosphere
Because water covers three-quarters of the earth’s surface, it might appear that there is plenty to go around and that we will never run out of this valuable resource. In reality, however, we have a limited amount of usable fresh water. Over 97 percent of the earth’s water is found in the oceans as salt water. Two percent of the earth’s water is stored as fresh water in glaciers, ice caps, and snowy mountain ranges. That leaves only one percent of the earth’s water available to us for our daily water supply needs. Our fresh water supplies are stored either in the soil (aquifers) or bedrock fractures beneath the ground (ground water) or in lakes, rivers, and streams on the earth’s surface (surface water).
We use fresh water for a variety of purposes. Worldwide, agriculture accounts for 70% of all water consumption, compared to 20% for industry and 10% for domestic use. In industrialized nations, however, industries consume more than half of the water available for human use.
Water scarcity
Water scarcity already affects every continent. Around 1.2 billion people, or almost one-fifth of the world's population, live in areas of physical scarcity, and 500 million people are approaching this situation. Another 1.6 billion people, or almost one quarter of the world's population, face economic water shortage (where countries lack the necessary infrastructure to take water from rivers and aquifers).
Water scarcity is among the main problems to be faced by many societies and the World in the 21st century. There is enough freshwater on the planet for the seven billion people that live on Earth today but it is distributed unevenly and too much of it is wasted, polluted and unsustainably managed. By 2050, the world's population will have grown from 7 to 9 billion. This enormous upsurge means the need for water will increase by over 50 percent, if we continue our consumption at the current rate.
Water is at the core of healthy ecosystems and for human survival itself. Water is also at the heart of adaptation to climate change, serving as the crucial link between the climate system, human society and the environment. Spain uses its natural water resources intensively, mostly in agriculture, thanks to a highly developed dam infrastructure. The limits for extraction of natural resources have largely been reached and climate change is expected to continue lowering natural water endowments markedly in future especially in dry areas of the country.
The costs of exploiting alternative supply sources on a large scale, notably desalination and recycling remain well above water prices paid by consumers at present in Spain. Scope for water savings is substantial, especially in agriculture, where much irrigation water generates little value-added. Further steps need to be taken to halt excessive groundwater exploitation.
At the household level, simple measures like turning the tap off when water is not being used or using a dual flush toilet can help to save water.
Water Pollution
Water pollution contributes to lowering the amount of water available for human consumption. To eliminate part of the pollution coming from households, factories and commercial buildings, water goes through water treatment plants, so that water can be disposed into rivers and the sea. If pollution is not eliminated:
Contamination from pesticides causes reproductive damage within wildlife in ecosystems.
Sewage, fertilizer, and agricultural run-off contain organic materials that when discharged into waters, increase the growth of algae, which causes the depletion of oxygen. The low oxygen levels are not able to support most indigenous organisms in the area and therefore disrupt the natural ecological balance in rivers and lakes.
Industrial chemicals and agricultural pesticides that end up in aquatic environments can accumulate in fish that are later eaten by humans. Fish are easily poisoned with metals that are also later consumed by humans. Mercury is particularly poisonous to small children and women
The water cycle
or ice, some of the water may evaporate back into the air to form clouds, while other parts of the water may penetrate the soil and become groundwater. The groundwater can either return to the atmosphere and form clouds via transpiration, or it can flow into oceans, rivers, streams and other bodies of water. The cycle then begins again, with water evaporating from earth’s bodies of water.
This is how the earth's water recycles itself. When water evaporates, it leaves all the pollutants behind, preventing a build-up of them that would render water not safe to drink. If there was no water cycle - water would evaporate but then none would form clouds, none would fall as precipitation, none would fill up the lake/streams, eventually it would all evaporate and we would run out of water. The water cycle brings water to plants, animals, including us, it moves nutrients and sediment in the different aquatic ecosystems and it is linked to climate as it involves atmosphere, oceans and land
Importance of water for life
Everybody knows that liquid water is necessary for life, at least as we know it. But just why exactly? The biochemical reactions that sustain life need a fluid in order to operate. In a liquid, molecules can dissolve and chemical reactions occur. And because a liquid is always in flux, it effectively transport vital substances like nutrients from one place to another, whether it's around a cell, an organism, an ecosystem, or a planet. And why is water the best liquid to do the job?
For one thing, it dissolves just about anything.
Water plays another key role in the biochemistry of life: bending enzymes. Enzymes are proteins that catalyze chemical reactions, making them occur much faster than they otherwise would. To do their work, enzymes must take on a specific three-dimensional shape and it is water molecules that facilitate this.
Next to mercury and liquid ammonia, water is our only naturally occurring inorganic liquid, the only one not arising from organic growth. It is also the only chemical compound that occurs naturally on Earth's surface in all three physical states: solid, liquid, and gas. Good thing, otherwise the hydrological cycle that most living things rely on to carry water from the oceans to the land and back again would not exist. Water also has an extremely large liquid range (from 0ºC to 100ºC)
Water also has one of the highest specific heats of any substance known, meaning it takes a lot of energy to raise the temperature of water even a few degrees. That provides a very stable environment for the cell’s reactions to take place.
Geosphere
Geosphere refers to the solid parts of the Earth; it is used along with atmosphere, hydrosphere, and biosphere to describe the systems of the Earth.
The Earth: a layered body
The interior of the Earth is a layered body. To a first approximation, it consists of concentric shells: the core, the mantle, and the crust.
The core consists mostly of iron, alloyed with a small percentage of certain other chemical elements. The outer part of the core is liquid, and the inner part is solid.
The mantle constitutes the greater part of the mass of the Earth, has its lower boundary, with the core, at a depth of about 2900 km. (The radius of the Earth is about 6400 km.) The mantle consists almost entirely of solid rock (there is a widespread and thoroughly mistaken belief that the upper mantle is everywhere molten.) Saying that the mantle is solid rock, true as that statement is, is somewhat misleading, though, because the solid rock of the mantle can flow plastically. You see the same kind of behavior in glacier ice, for example. The uppermost part of the mantle, however, is sufficiently cool that it behaves not as a very stiff liquid but as a rigid solid. This situation, whereby the uppermost rigid part of the mantle (which, together with the overlying crust, is called the lithosphere) rides on the plastically flowing part of the mantle beneath, is the basis for what is called plate tectonics
The crust: The uppermost skin of the Earth, above the mantle, is called the crust. There are two basic kinds of crust, very different from one another in properties and origin: oceanic crust and continental crust. Oceanic crust is relatively thin, seldom more than seven to eight kilometers. Continental crust, on the other hand, is relatively thick, mostly thirty to fifty kilometers. The lithosphere, the outermost part of the Earth, comprising the crust and the uppermost, rigid part of the mantle, is in the form of a number of segments, called lithospheric plates (or just plates), which are in contact with one another along what are called plate boundaries. The movements of these plates, and the consequences of those movements, especially in terms of what happens at plate boundaries, are collectively termed plate tectonics.
Why the interior of the earth is divided into layers?
The earth is separated into layers because of gravity and density. Gravity is the attractive force that anything made of matter has toward anything else made of matter. Density is mass per unit volume. You can think of it as how heavy something feels in your hand compared to how heavy something else is that is the same size. Something that is less dense is lighter than something else of the same size that is more dense.
a lot of pressure from the rocks above. The lowest layer of the earth is the core, which is a very dense layer made of iron and nickel.
Materials on the Earth’s crust
The most abundant element in the universe is hydrogen (H), which makes up about 3/4 of all matter. Helium (He) makes up most of the remaining 24%. Oxygen (O) is the third most abundant element in the universe. All of the other elements are relatively rare. However, the chemical composition of the Earth is quite a bit different from that of the universe. The most abundant element in mass in the Earth's crust is oxygen (O), making up 46.6% of the Earth's mass. Silicon (Si) is the second most abundant element (27.7%), followed by aluminum (Al) (8.1%), iron (Fe) (5.0%), calcium(Ca) (3.6%), sodium(Na) (2.8%), potassium(K) (2.6%). and magnesium(Mg) (2.1%). These eight elements account for approximately 98.5% of the total mass of the Earth's crust.
Minerals
The definition of a mineral is: a naturally occurring crystalline solid. By “crystalline” is meant that the atoms of the mineral are arranged in a regular three dimensional array, called its crystal structure.
Most of the common minerals are of a class called silicate minerals. Silicate minerals have as their basic building blocks a silica tetrahedron, that consists of one atom of silicon, relatively small, surrounded by four atoms of oxygen, relatively large, to give the shape of a tetrahedron. The five atoms are bonded very strongly together. The reason why silicate minerals are so common is that, in terms of abundances of the 76 chemical elements in the crust, oxygen is the number one and silicon is second.
Rocks
Rocks are naturally occurring aggregates of minerals. However, that definition is not very revealing of the nature and variety of rocks. There are three kinds:
Igneous rocks are those that form by cooling and solidification of magma. Magma is the term for melted rock in the Earth’s interior. At certain times and in certain places in the Earth’s shallow interior, down to a hundred or so kilometers, the rocks of the upper mantle or lower continental crust melt, to form magma. The melting is only partial, commonly up to fifteen to twenty percent of the rock, but the magma collects and then moves upward owing to its buoyancy (it’s slightly less dense than the surrounding rock). It either becomes parked in subsurface spaces, called magma chambers, there to cool slowly, creating rocks like granite, which have large minerals that can be seen with the naked eye; or it rises all the way to surface to be ejected from volcanoes, where magma is cooled quickly. Quick cooling magmas have small minerals, which are barely distinguished with the naked eye.
Sedimentary rocks are those that form from sediments that are deposited at the Earth’s surface and turned into solid rock, by a variety of processes as they are buried more and more deeply in the earth’s crust. Sedimentary rocks vary widely in composition and origin. There are two major types of sediments and sedimentary rocks: clastic and chemical. Clastic sediments and rocks are those that consist of clastic material ((pieces of other rocks or fragments of skeletons) which have become cemented together (eg, conglomerate). Chemical rocks are those formed by chemical mechanisms including precipitation and evaporation (eg, limestone).
Metamorphism refers to changes in mineral composition7 or rock geometry that occur in solid rocks with increasing temperature and pressure. These changes produce a rock called metamorphic rock. Most metamorphic rocks show some degree of what is called foliation: development of planar features in the rock, like layering or a tendency for the rock to split along parallel planes. It is important to remember that changes producing metamorphic rocks take place while the rock is solid. Any part of the rock that is melted eventually cools to form an igneous rock.
Examples of observable features in rocks
Rock Type
Characteristics Observable Where Formed Example1. Igneous
Volcanic Crystals so small you can't see them with the unaided eye.
These rocks were once liquid magma that erupted from volcanoes. They cooled very quickly, which is why the crystals are usually very small.
Basalt – usually white,
fine-grained volcanic rock;
sometimes has gas bubbles.
Plutonic Interlocking Crystals
These rocks were once liquid magma, but they did not erupt from volcanoes. Instead, they cooled slowly underground. The crystals had time to grow large. We see them because erosion has stripped off and removed all of the rock above it.
Granite – pinkish, whitish igneous rock with interlocking crystals.
2. Sedimentary
Clastic Made up of smaller rocks cemented together. Sometimes has fossils.
These rocks formed when loose
sediment (rocks, sand) were
deposited by water, compacted, and cemented together.
Conglomerate – composed of pieces pebble-size or larger Sandstone - composed of sand-size pieces
Chemical Usually a light gray, sometimes with crystals, sometimes with shells, sometimes just massive.
These rocks are also deposited in water. They form as a chemical reaction in the water that leaves a chemical deposit, usually on an ocean bottom.
Limestone – a whitish or grayish rock
3. Metamorphic
Usually has interlocking crystals
and layers (called foliation)
These rocks formed when igneous, sedimentary, or other metamorphic rocks are heated and/or squished, forming a new rock type.
Quartzite – from sandstone
Slate – from shale.
Schist – from sedimentary rocks that had lots of clay.
Gneiss – from granite.
Common uses of rocks and minerals
When people want something, we rarely think about the source of materials that are necessary to make that product. All we see is the end product. Everything you want or buy that is tangible has to be made of something, and that something is materials from our natural resources. Most of it is made from minerals, metals and petrochemicals. Some of the most widely used minerals and rocks are:
Lead coming from the mineral galena: Primarily used in the construction of car batteries
Zinc coming from several minerals: primarily used as a rust inhibitor for steel in the construction of cars, buildings, bridges, ships and trains.
Aluminium coming from the mineral bauxite: it is the most abundant metal element in Earth's crust. Used to make cans, aircraft and automobile construction.
Iron coming from different minerals: it is used to make steel
Clay minerals: it is used to make bricks.
Salt coming from halite: used in food preservation, to enhance the taste of foods and to melt the ice on streets and highways during the winter.
Stone, sand, gravel and cement: they are used in streets, highways and sidewalks; in the foundation for your house and school.
Aggregate (it is what pieces of rocks that have been blasted is called) The gravel you see in driveways & at the side of the road are aggregate. Sometimes you won't see aggregate because it has been mixed with cement to make concrete - the grey "stuff" that sidewalks, buildings and curbs are made of. Aggregate can also be mixed with tar and other ingredients to make asphalt to pave roads.
Coal and crude oil: coal is primarily used in the generation of electricity. Crude oil can be used as the raw material of different types of fuel, fertilisers/pesticides, plastics, synthetic fibers, synthetic rubber, dyes, paint, etc.
Gypsum: one of its primary uses is in the manufacture of "sheetrock" or wallboard.
Granite, Marble and Shale: they are used to decorate the outsides of buildings as well as tiles for floors and counters.
Sustainable use of rocks and minerals
The great economic growth experienced throughout the 20th century by many countries is mainly supported by the increasing extraction of natural resources, favored by technological innovation. The current exponential growth cannot longer be supported as minerals and rocks become depleted.
Peak minerals marks the point in time when the largest production of a mineral will occur in an area, with production declining in subsequent years. The graph on the left shows that, while most mineral resources will not be exhausted in
the 21st century.
