Rock solid. Steady as a rock. Rock hard.
Have you noticed it? Whenever we want to describe something permanent, immovable, or resilient we invariably drag rocks into it. And this is not true of the English vocabulary alone. It is, in fact, an inherent part of every language that human beings speak, across the planet.It is not difficult to figure out why rocks feature so conspicuously in our dialogues. Solid stones were the basic building blocks of all human civilisations. Towns, cites, roadbeds, bridges, houses — flagship of a thriving urbane society — were all carved out of rocks.
Even the primitive humans lived in caves with stonewalls that kept the predators at bay. Rocks are a natural resource that makes up the Earth’s layers and the crust. They are found everywhere, and are a part of all human activities. They produce energy (coal is a rock too!); yield useful minerals; and serve as raw material for concrete. Others serve for toolmaking, from the stone knives of our pre-human ancestors to the chalks used by artists today. The canvas of stones is vast and eternal. Let’s explore some parts of it...
The three types of rocks:
However, there are no set rules to separate the rocks types. By altering the proportions or properties of their minerals, they change into one another. So, they are merely different points of the continuous series of a rock cycle.
Rocks are naturally occurring combinations of minerals. They can be hard or soft, as small as a grain or as large as a building. Stones are small-sized rocks or their fragments. Rocks are classified by mineral and chemical composition, by the texture of the constituent particles and by the processes by which they were formed.
These indicators separate them into igneous, sedimentary and metamorphic. The natural transformation of one rock type into the other is known as rock cycle. Igneous rock can change nto sedimentary rock or into metamorphic rock. Sedimentary rock can change into metamorphic rock or into igneous rock. Metamorphic rock can change into igneous or sedimentary rock. The cycle never stops. Say, an igneous rock is broken into pieces by wind and water.
The same forces carry these rock pieces to another place where they make a layer. The depositions cement together to make a sedimentary rock. In this way, an igneous rock becomes a sedimentary rock. And if heat and pressure is applied to this rock, it may change into a metamorphic one! So, what role do rocks play in our lives?
Rocks are everywhere. Quite literally.
Rock… a hard, harsh, useless substance… found in mountains… Or the popular music genre! Rocks conjure up images of all these. But, they are much, much more!
All of us have heard about comets, asteroids and meteoroids… right? Do you know that these are the three main types of rocks found in space?
The ones that are larger are called minor planets or planetoids. These are also known as Near Earth Objects (NEOs). All these rocks reveal a lot about our solar system, including its origin!
Comets are bodies of ice, rock, gas and dust. A small one is about the size of a house! They probably originated in a cold area beyond Neptune and Pluto called the Oort Cloud, which surrounds the solar system.
Another area where comets are found is called the Kuiper Belt, which lies just past Neptune’s orbit. Comets follow a regular orbit around the Sun. They journey on a trail that may take 200 years to complete! And these are just short-period comets!!!
As old as rocks
Rocks are part of history, and also, a witness of it. Human history is preserved in them. Rock layers (or strata) are laid down or deposited in succession, and each represents a ‘slice’ of time. This is the underlying principle of a model used by geologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of Earth.
It is known as the geological time scale. Fossils are the preserved remains or traces of animals, plants, and other organisms from the remote past. They are found in fossiliferous (fossil-containing) rock formations and sedimentary layers (strata). William Smith, a leader in British geology, realised that rock layers can be identified by the fossils they contain.
In 1815, he produced a geologic map of England in which he demonstrated that fossils are found in rocks in a very definite order. This helped to correlate geographically distinct areas. And shaped the geological time scale of Earth. So, that’s how we know HOW old is our planet (about 4.570 billion years)!
Asteroids are odd-shaped heavenly bodies that are made of rock. Some of them are also made of metals such as nickel and iron. Their size can vary – from merely a couple of metres to several hundred kilometers across. The largest asteroid, Ceres, is 960 kilometres wide! Because of their size, asteroids are sometimes called minor planets or planetoids. Some asteroids even have moons that orbit them.
Most asteroids orbit the Sun in a region between Mars and Jupiter – the Asteroid Belt. Sometimes, they even venture into Earth's orbit.
The “solid” part of Earth, covering the Crust and the Upper Mantle, is known as lithosphere. It is about 100 km thick. And it is made of rocks. All geological phenomena happen because of this rocky layer. How?
Well, the lithosphere is broken up into tectonic plates, like slices. There are seven major and many minor plates on Earth. These plates move in relation to one another. And their movements lead to earthquakes, volcanic activity, mountain-building, and oceanic trench formation. This happens in three ways…
They either move horizontally by gliding overasthenosphere, the layer below lithosphere, creating earthquakes and transform faults. Or they collide with each other at the plate boundaries, which produce earthquakes, volcanoes, mountain building and oceanic trenches. Or they may also move away from each other because of sea-floor spreading. So in a way, rocks are the main reason behind these geological phenomena!
Rocks are not only a part of our planet, but also of our history. Remember reading about the Stone Age in History books? Yes, the prehistoric time period during which human beings widely used stone for tool-making.
The Stone Age covers the Paleolithic, the Mesolithic, and the Neolithic periods. It ends with the development of agriculture, the domestication of certain animals and the smelting of copper ore to produce metal.
The tools were made from a variety of stones. For example, flint and chert were shaped (or chipped) for use as cutting tools and weapons, while basalt and sandstone were used for ground stone tools, such as quern-stones.
Also, sediments (like clay) were used to make pottery. The shaping, chipping or flaking of stones for making tools is known as Flintknapping. And it is the world’s oldest documented profession. So, stone or rock is the beginning of technology, and its use in tool-making is the oldest art preserved in the archaeological record.
A Rock we Eat
Sounds bizarre? May be not…
We eat edible rock salt, and use it for cooking. It is used to bake meats and vegetables like potatoes. But, its best use is in making ice cream! The salt lowers the freezing point of the ice, which causes it to melt.
Melted ice water is much better at absorbing the heat from the ice cream mixture than ice cubes and this makes the ice cream freeze faster. Apart from its edible version, rock salt is also used in other applications as Halite. It is mainly used to manage ice.
In cold countries, it helps to clear roads of ice during winter, because of its ice-melting property.
The beauty of rocks is also revealed through art. Before writing was developed, symbols were used for communication. One of the most dominant forms was Petroglyphs.
A Petroglyph is an abstract or symbolic image recorded on stone by means of carving, pecking or incising on natural rock surfaces. They appeared in the New Stone Age or Neolithic period. Another major form was that of rock paintings.
These were ‘painted’ on rocks and were more naturalistic depictions than petroglyphs. In Paleolithic times, human figures were rarely painted, instead animals were depicted.
Signs like dots were sometimes drawn. Rare human representations include handprints, and half-human and halfanimal figures. The meaning of most of these paintings remains unknown.
All of us know the importance of mining for the advancement of human civilisation. So, realise how important rocks are?
Rocks have always been and continue to be used to construct buildings and infrastructure. They are generally used as dimension stone or crushed stone.
Dimension stone is a natural stone or rock that has been selected and fabricated (trimmed, cut, drilled, ground, and so on) to specific size or shape.
A variety of igneous, metamorphic, and sedimentary rocks are used as dimension stone. The favourites are granite, limestone, marble, travertine, quartz-based stone (sandstone, quartzite) and slate. In addition, rocks and stones that are not considered to be dimension stone are also available, such as tiles made of jade, agate, and jasper.
A major plus of using dimension stones is “eco advantage”. Green building (environment-friendly construction) with natural materials has gained limelight these days. Dimension stone production is less energy intensive than that of concrete, aluminum and steel. It as an entirely natural product, and is recyclable and re-usable.
The Map that changed the world
"If geology were a religion, this map would be its bible," But the world's first geologic map – geological map (of the British Isles) – by the renowned geologist William Smith in the 19th century isn't only for geologists.
It directly addresses the relationship of people to the natural world. It influenced the industrial revolution, geology, biology and evolution. It forced people to think about our place in the universe.
How have geologists determined that:
● Earth is about 4.6 billion years old?
● The oldest known fossils are from rocks deposited about 3.5 billion
● The first abundant shelly fossils occur in rocks that are about 570 million years old?
● The last ice age ended about 10,000 years ago?
How to Read Rocks
Rocks are solid, natural aggregates of mineral. Glass also found in many volcanic types. Minerals combine different ways to make rocks. They are the words Earth's history book: in each rock, they tell a different story. So get outdoors and start rocking!
What you need
First you need to examine rocks and learn to identify igneous, metamorphic and sedimentary rocks. Look around, you will surprised at the variety and kinds.
People who study Earth's history also use a type of calendar, called the geologic time scale. It looks very different from the familiar calendar. In some ways, it is more like a book, and the rocks are its pages. Some of the pages are torn or missing, and the pages are not numbered, but geology gives us the tools to help us read this book.
What on earth is time? Find a fossil in a rock, and you would know. Living creatures, once widespread, became extinct. They are preserved in rocks. Only a small percentage of fossils meet these criteria. Paleontologists look for fossils in sedimentary rocks to figure out the rocks’ age based on the worldwide geological time scale defined by fossils. In the 20th century, geologists made a timely discovery: rocks contain atomic clocks.
They enable geologists to calculate when a rock formed — its absolute age — by measuring its radioactive elements. Try and locate real fossils (right) or examine a variety of fossils in a museum or learn about them on the net and in books. Explore the concepts of stratification and its relation to fossils.
Minerals are more than beautiful display pieces. They are the very building blocks of the universe. Minerals make up the Earth, the Moon, and the meteorites that voyage to Earth from other parts of the Solar System. They hold the tangible evidence scientists need to learn about our world. Modern civilisation relies heavily on mineral resources.
You use minerals more than you may imagine. Find out what minerals exist in your regions. See that minerals have different colors and hardnesses. Record your findings in your field guide. Dig the soil to look at the particles and find out what lives there. Ask your parents and teachers about expert geologists in your town or city. Interview them. Get inspired to tell the stroy of our earth.
Crushed stone or angular rock is a form of construction aggregate. Construction aggregates are coarse particulate material used in construction. They serve as reinforcements, and add to the strength of the basic materials. They are also used as foundation under roads and railroads. Crushed stone is the key component used in construction, agriculture, and other industries. It is usually produced by breaking a mined rock into the desired size using crushers. Thus, it is distinct from gravel, which is produced by natural processes of weathering and erosion. It substitutes the use of other aggregates like sand, gravel and slag (by-product of smelting ore to purify metals).
Some rock structures have gained so much of fame that they have even become a “symbol” of the country they are built in. Can’t recall any names? Here’s one – Taj Mahal. Yes, Taj Mahal is built with rocks, specifically dimension stones – marble. Some Egyptian pyramids are also made of stones or rocks. Even the Great Wall of China is a series of stone and earthen fortifications.
Apart from these monuments, rock gardens are also a world-favourite. A rock garden, also known as a rockery or an alpine garden, is a type of garden that features extensive use of stones, along with plants native to rocky or alpine environments. But, the Japanese rock garden is a special kind with hardly any plants. And in India, the Rock Garden in Chandigarh is a sculpture garden. Spread over an area of forty acres, it is completely built of industrial and home waste and thrown-away items!
Rocks are treasure troves. Literally. Some are valued for their beauty or aesthetic sense. These are called gemstones. Gems (also called precious or semi-precious stones) are pieces of attractive mineral, which are used to make jewellery and other adornments after cutting and polishing. However, certain rocks, such as lapis-lazuli are not minerals, but are often considered as gemstones. Rarity is another characteristic that lends value to a gemstone.
So, aren’t rocks simply incredible? But do you know that even the slightest change in the environment can spell doom for them?
Remember the rock cycle? Yes, the changing of one rock type into the other. This is a natural process that depends mainly on the forces of wind and water. They help to erode and weather rocks.
Weathering is the process of chemical or physical breakdown of rock minerals. Erosion, on the other hand, is the carrying away (displacement) of rocks by forces like wind and water. But, the two processes may be concurrent. Erosion is greater in areas with highly weathered rock.
The rate of erosion is affected by various factors. One of them is human activity. Poor land use practices like deforestation, overgrazing, and unmanaged construction activity destroy the ground cover from vegetation. This exposes the rocks to the forces of erosion. Further, changes in the climate, such as the average temperature, and the amount and intensity of rain, worsen the situation.
Erosion wears down mountains. This develops massive piles of sediments in the nearby lands and water bodies. Excessive deposits cause a lot of problems like disrupting the flow of water and ecosystem damage.
The removal of large amounts of rocks from a particular region, and its deposition elsewhere, can alter the load on the lower crust and mantle. This can cause tectonic uplift in the eroded region. In other words, the land would rise to compensate the loss of weight of rocks.
As for weathering, one of the major factors that accelerate its pace is acid rain – any form of precipitation that is unusually acidic. The acid deposition may be wet (rain, snow, sleet, fog or dew) and dry (acidifying particles and gases) acidic components.
Apart from adversely affecting our health, forests, freshwaters and soils, killing insect and aquatic life forms, acid rains damage structures, especially those made of rocks. And mountainous regions are the most-affected, simply because they get more rainfall.
This poisonous precipitation is mainly caused by human emissions of primary air pollutants, mianly sulphur and nitrogen compounds. These react in the atmosphere to produce acids like sulphuric and nitric acid. The main sources of these pollutants are industrial powergenerating plants and vehicles.
So you see, rocks shape our lives and we shape theirs. Most often, through activities that affect rocks adversely. It may be pollution, climate change or deforestation, all erode and weather away these treasure troves.