Nature’s Treasures: Class 6 Science · Chapter 11

Treasures all around us

What did you use this morning before school? Maybe you gulped a glass of water, ate a hot roti and sharpened a pencil. Then you climbed onto a bus or an auto. None of these began in a shop. Every one of them started out in nature.

Scientists call such useful things from nature natural resources. They are nature's treasures. Unlike gold coins locked in a chest, many of them are free and lie all around us. Every fish, every fern and every child on Earth is kept alive by them. And we do not just use nature from the outside. We belong to it, just like every ant and every banyan tree.

In this chapter we go on a treasure hunt. We start with three treasures we cannot do without for even a day: air, water and sunshine. Then we walk into forests, dig into soil and rocks, and find out where petrol comes from. Last, we sort the treasures into two groups and learn how to keep them safe.

11.1 Air

Hold your palm in front of your mouth and breathe out. You can feel air, even though you cannot see it. You breathe in and out all day and all night, even in deep sleep. Why can you never take a break?

What is air made of?

Air is not one single gas. It is a mixture of several gases, all jumbled together. Imagine you could catch a scoop of air and count 100 of its tiny particles. Fig. 11.2 shows what you would find.

Most of the air is nitrogen. Next comes oxygen, the gas we need for breathing. The last tiny share holds argon, carbon dioxide ($\mathrm{C}\mathrm{O}{\phantom{X}}_2$) and a few other gases. Tiny as it is, that carbon dioxide matters: green plants take it in to make their food.

Air on the move

Air is invisible, yet it leaves clues everywhere. A kite strains at its string on Makar Sankranti. A dupatta streams out of an auto-rickshaw window. On a hot summer afternoon, a dust devil whirls across a dry field. Each clue tells you that air is on the move.

Winds come in all strengths. On a hot evening in Chennai or Mumbai, a cool breeze drifts in from the sea. In a cyclone, the wind roars so hard that it can uproot trees and rip off tin roofs. Gentle or wild, moving air pushes on whatever is in its way. That push is energy we can use.

Now picture a firki as tall as a 30-storey building. That is a modern wind turbine, like the one in Fig. 11.3. Each blade can be longer than a cricket pitch. The wind turns the blades, and they spin a machine in the box at the top that makes electricity. Where strong winds blow for most of the year, rows of turbines stand together on hills and coasts. Such a place is a wind farm. Smaller, older windmills did simpler jobs, like lifting water from wells or grinding grain.

11.2 Water

Water is the busiest treasure in your home. Before breakfast it has probably already brushed your teeth, boiled the tea and washed a pile of steel tumblers. Outside your home it works even harder.

• In the fields: paddy fields flooded for rice, thirsty sugarcane, and drinking water for cows and buffaloes. Farms use most of the freshwater that India takes from its rivers and wells.
• In factories: making paper, cloth, medicines, bricks and steel.
• On rivers and lakes: boats carrying goods and people, fishing, and the snake-boat races of Kerala.
• Back at home: tea, dal and rice, a bucket bath, clean dishes and a mopped floor.

Where is Earth's water?

From space, our planet looks blue. Seas and oceans spread over most of it, about 7 parts of every 10 of its surface. So why do so many towns run short of water every summer? The answer is salt.

Imagine pouring all the water on Earth into one 1-litre bottle, as in Fig. 11.4. Almost the whole bottle is sea water. Gulp it and you would feel sick and even thirstier. Pour it on a wheat field and the plants would wilt. People, crops and most land animals need freshwater, which has very little salt in it.

Now look at the tiny cup of fresh water in the figure. Most of it is locked away. The biggest part is frozen, in the ice sheets near the poles and in Himalayan glaciers. The next biggest part lies underground, soaked into sand and rock. Wells and hand pumps reach only the top of this store. Rivers, lakes and ponds, the water lying open where we can easily reach it, hold just a drop or two of the litre. Every person, plant and land animal must share it.

Stop the leaks

Freshwater is scarce, yet we often let it run away. A tap left open while you brush pours out several litres every minute. A dripping tap can fill a bucket in a day. Time to play detective at home.

Keep it clean

Saving water is only half the job. We must also keep it clean. A river collects whatever we let into it. Sewage from towns, chemicals from some factories, fertiliser washed off fields and heaps of plastic all end up downstream.

Adding harmful things to water, air or soil is called pollution. A single glass of dirty river water can carry germs that cause stomach upsets and fever. Fish gasp and die in it too. Cleaning a dirty river takes years and costs a great deal, so it is far wiser to keep it clean from the start.

Water is not shared out fairly, either. In some homes a tap runs all day. In a dry village a few hours away, a girl may spend an hour before school carrying pots of water home. In summer, city lanes fill with rows of plastic pots waiting for the water tanker. Every litre one of us wastes or dirties is a litre someone else must go without.

Catch the rain

Every monsoon, huge amounts of rain fall on rooftops, roads and playgrounds. Most of it rushes into drains and away. What if we could gather it in, the way a farmer gathers in a crop? That is the idea behind rainwater harvesting: catching rain where it falls and saving it for later.

Water from the tank can be used for washing, flushing and gardening, and after proper cleaning even for drinking. Water that soaks down through a recharge pit adds to the store of water under the ground. Wells and hand pumps nearby then keep giving water further into the summer. Since 2003, Tamil Nadu has required buildings to catch the rain that falls on them. Does your school catch its rain?

Long before taps and tankers, people in India's driest regions built their own answer to thirst: the stepwell. Picture a huge stone funnel sunk deep into the ground, with flights of steps running down its sides to a pool at the bottom. In Rajasthan it is called a baori or bawadi; in Gujarat, a vav. Monsoon rain pours in from above, and more water oozes in sideways through gaps in the stone walls, from the soaked earth all around.

The steps are the clever part. As the water level falls in the dry months, people simply walk further down. Chand Baori at Abhaneri in Rajasthan has about 3,500 narrow steps, and Rani ki Vav at Patan in Gujarat is carved with hundreds of stone figures. Many towns are now cleaning and reviving their old stepwells and tanks.

11.3 Energy from the Sun

On the beaches of Kerala and the Konkan coast, fishers spread their catch on mats to dry in the sun. In Punjab, families dry vadiyan on the rooftop in winter. A few days of strong sunshine and the food is dry enough to store for months. How does the Sun manage this? Its heat makes the water in the food evaporate, just as it dries puddles and wet clothes.

Drying is just one job the Sun does for us. The Sun sends us two gifts, heat and light. Fig. 11.9 follows one Indian rooftop from morning to night.

Machines that run on solar energy catch either its heat or its light. A solar cooker, a box with a shiny lid and a glass cover, traps heat and cooks dal slowly. A solar water heater warms water in dark pipes, ready for a morning bath. A solar panel catches light and turns it straight into electricity. In many villages, solar pumps now lift water into the fields. The airport at Kochi in Kerala even runs on power from its own solar panels.

The Sun feeds us all

Sunshine warms the lizard's cold body, so its muscles can work fast. But warmth is not food. The energy the lizard uses to run and hunt comes from the insects it eats. Those insects fed on leaves, and the leaves made their food using sunlight. So the Sun is behind the lizard's energy after all, through a chain of eaters rather than through basking.

That is why we say almost all the energy for life on Earth comes from the Sun. Plants catch its light and store the energy in food. Every animal, including you, gets energy by eating plants or by eating animals that ate plants. The Sun also warms the land and seas, drives the winds and lifts water into the clouds.

11.4 Forests

Step into a forest and the air feels cooler and damp. Tall trees spread a green roof overhead. Beneath them grow shrubs, climbers, ferns and small herbs. Birds call, insects hum and a squirrel scolds you from a branch.

India has many kinds of forests. Mangroves grow in the salty mud of the Sundarbans. Pine and deodar forests cover Himalayan slopes, and dry, thorny forests dot Rajasthan. Evergreen rainforests stay green all year in the Western Ghats and the North-East. Each one gives us gifts.

A forest works like a busy village where everyone has a job. Deer graze on grass, and tigers hunt deer. Hornbills gobble figs and drop the seeds far away, where new trees sprout. Fungi slowly turn fallen logs back into soil. And if one kind of food runs short, animals can often find another.

Over the last hundred years, huge areas of forest have been cleared for farms, mines, dams, roads and towns, or simply for their timber. Cutting is quick; regrowing is slow. A teak tree felled in an hour may be 50 years old. If we take trees faster than new ones grow, the forest shrinks year after year.

Forests also guard the soil, as Fig. 11.11 shows. Tree roots grip the soil like thousands of fingers. Fallen leaves cover the ground like a blanket, so heavy rain soaks in slowly instead of rushing away. Where the trees are cleared, rain can strip away the top layer of soil in just a few seasons.

Forests feed their own soil too. Dead leaves, twigs and fruits pile up on the forest floor. Earthworms, fungi and tiny living things break them down into a dark, crumbly layer called humus. Humus is full of the nutrients that young plants need. In this way a forest is its own compost pit, and nothing goes to waste.

11.5 Soil, Rocks and Minerals

Before sowing, farmers plough their fields and gardeners dig their beds. Why go to all that trouble? Hard, packed soil has few gaps between its grains. Loosened soil is full of tiny spaces that hold air and water, and young roots can easily push through them.

So soil is a mix of many things. It holds tiny bits of rock such as sand and clay, and humus from rotted plants and animals. Air, water and a crowd of living things fill the gaps. Why is one soil red and another nearly black? It depends on the mix. Red soil gets its colour from iron, while black soil is dark and sticky with clay.

How is soil made?

Soil starts out as rock. Heat, cold, water and living things break the rock down, so slowly that you would never notice it in a lifetime. Fig. 11.13 shows the main steps.

How slow is slow? Nature may need a few hundred years, or even longer, to build a layer of soil just 2–3 cm thick. Soils also differ from place to place. Potters and brick-makers dig sticky clay, because it can be shaped when wet and baked hard. Farmers prize other soils. The black soil of the Deccan holds water well, so cotton grows in it. Rivers have spread soft, fertile soil across the Ganga plains, where wheat and rice grow.

Rocks

Look around your town and you will find rocks everywhere, often in disguise. The gravel under a railway track is rock. So are the slab beside a kitchen sink, the shiny floor of a hotel lobby and the stone for grinding chutney. The carved pillars of an old temple are rock too.

Rocks have served people for a very long time. More than a million years ago, early humans near present-day Chennai shaped hard stones into hand axes. Much later, people chipped small, sharp arrowheads for hunting. Stone tools like these have been dug up at many places in India.

A quarry can slice away a whole hill in a few years. No new hill will rise in its place for millions of years. Rocks are a treasure to use carefully. Reusing old bricks and stones in new buildings is one good way to save them.

Minerals

Break a rock and look at it closely through a lens. You may see tiny grains of different colours: some glassy, some pink, some black and shiny. Each kind of grain is a mineral. Rocks are made of minerals.

Many metals come from minerals dug out of the ground. Iron comes from minerals mined in Odisha, Jharkhand and Chhattisgarh, and aluminium from a mineral called bauxite. Copper, silver and gold have their own minerals. The steel of a railway line and the silver in a pair of anklets both began inside rocks. Even a kitchen shelf is full of minerals, as Fig. 11.14 shows.

Minerals form over very long times, and there is only a fixed amount in the ground. When old phones, wires and pots are recycled, their metals can be used again instead of digging up more rock. That is one good reason never to throw old gadgets in the dustbin.

11.6 Fossil Fuels

Stand near your school gate at 8 in the morning and watch. School buses rumble in, scooters buzz past, a green-and-yellow auto putters to a stop and a tractor chugs by with a trolley. Every one of them runs on some kind of fuel. Do they all use the same one?

Petrol and diesel are cousins. Both are made from petroleum, a thick, dark oil pumped up from far below the ground or the sea bed. So are kerosene and the LPG in kitchen cylinders. Petroleum belongs to a family with an odd name, the fossil fuels. Coal and natural gas are in the family too. Fig. 11.15 shows where the name comes from.

Think of a fossil: the remains or print of a living thing from long ago, kept safe in rock. Fossil fuels are made of such remains. Buried swamp plants turned into coal. Tiny sea creatures and plants turned into petroleum and natural gas. Each change took millions of years.

Fossil fuels come with two catches. Catch one is the stock. Nature makes new coal and oil far too slowly to matter to us. Every litre of petrol burnt today is gone for good. The coal clock below shows just how lopsided this is. Catch two is the smoke. Burning fossil fuels fills the air with soot and harmful gases, and the extra carbon dioxide traps heat and warms the Earth. That is why people are turning to the Sun, the wind and flowing water for energy.

11.7 Natural Resources: Renewable and Non-renewable

Look back over our treasure hunt, from the air in your lungs to the petrol in a scooter. People did not make any of these treasures. They were already here, and we found ways to use them. All such useful gifts of nature share one name: natural resources.

People turn natural resources into new things. Sand becomes window glass, iron ore becomes a railway track, and cotton becomes a school uniform. Useful things that people make in this way are human-made resources. A bridge, a pressure cooker and a mobile phone are all human-made, though each began with materials from nature.

Can nature refill it?

Nature keeps refilling some natural resources. Rain refills ponds and wells every monsoon. Green plants add oxygen to the air every day. A forest, if we take only a few trees at a time, grows new ones from seeds. Resources that nature renews within a reasonable time, roughly within a human lifetime, are renewable resources.

Many communities have long known how to use renewable resources wisely. Some traditional honey gatherers in the Nilgiri hills cut away only part of a honeycomb. They leave the rest, so the bees stay and make more honey. Along India's coasts, fishing boats stay ashore for about two months every year, while many fish breed. That way there are fish to catch the next year too.

Other resources cannot be refilled in any reasonable time. Think back to the coal clock: a fuel that takes millions of years to make can be burnt in a flash. Minerals and rocks also take thousands to millions of years to form. Even soil forms so slowly that a lost layer will not come back in our lifetime. These are non-renewable resources. Fig. 11.16 lines up both groups by how long nature takes.

Watch out: renewable does not mean endless. A forest stays renewable only if we cut trees no faster than new ones grow. A lake stays renewable only if we take out no more water than the rain puts back, and keep it clean. Try it for yourself below.

11.8 Resources We Use

On some winter mornings in Delhi, the sky turns grey and the air stings your eyes. You can barely see the end of the street. Where does this haze come from?

Smoke from vehicles, factories and power stations adds to it. So does smoke from burning rubbish and leftover crop stalks in the fields. Dirty air makes people cough, and over time it can harm the lungs, especially of children and older people.

Cleaner ways to travel are spreading. An electric bus or e-rickshaw has no exhaust pipe, so it puts no smoke into the street. The power station that charges it may still burn coal, though. CNG buses and autos pollute less than diesel ones. One metro train can carry more than a thousand people at once. And the cleanest trips of all are on foot or by bicycle.

We use natural resources every minute of every day, often without noticing. The next activity helps you spot them.

Every treasure in this chapter has a limit, even the renewable ones. So the rule is simple: take what you need, not all you can. Mend and reuse things before you throw them away, and keep air, water and soil clean. The children who will live in your town a hundred years from now are counting on you.

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