Unit 9 · Earth, Weather and Space

Step outside. Is the air hot or cold? Wet or dry? Still or windy? All of that is weather. Weather is the condition of the air at one place and one time. It can change in an hour. A sunny morning can become a stormy afternoon.

Scientists do not trust the word ’hot.’ Hot to one person is warm to another. So they measure. A thermometer measures temperature, how warm the air is. In the United States we use degrees Fahrenheit. Water freezes at 32 °F and boils at 212 °F at sea level.

A measurement is a number anyone can check. If you write 68 °F in a notebook every day at noon, you have data. After a month, you can see a pattern. That is the first job of a weather scientist: measure, write it down, and look for the pattern.

Rain, snow, sleet and hail are all precipitation. That long word just means water falling out of the sky. Rain is liquid drops. Snow is ice crystals. Hail is balls of ice built up inside a tall storm cloud. Sleet is rain that froze on the way down.

To measure rain, you need a rain gauge. It is a straight-sided tube with marks on it. Rain falls in, and you read the depth. If the tube shows 1 inch, then 1 inch of rain fell on every part of the yard. A bucket would not work well because its sides slope.

Snow is trickier. Ten inches of fluffy snow may melt down to only 1 inch of water. So weather stations measure snow two ways. They measure how deep it is with a ruler. Then they melt it and measure the water. Chicago gets roughly 38 inches of precipitation in a normal year.

Air is real stuff, even though you cannot see it. When air moves, we call it wind. Wind starts because the sun heats some places more than others. Warm air rises. Cooler air slides in to take its place. That slide is the wind you feel on your face.

A wind vane shows direction. Its arrow points into the wind. A north wind blows from the north toward the south. Wind is always named for where it comes from. An anemometer measures speed. Its little cups spin faster when the wind blows harder.

Wind direction is a clue. In Illinois, a south wind in spring often brings warm, wet air from the Gulf of Mexico. A north wind in winter brings cold air from Canada. Watch which way the flag on your school points. It is telling you something about tomorrow.

One day of weather is just one day. But a year of numbers tells a story. Look at Chicago’s average high temperature month by month. It climbs from winter to summer and falls again. That rise and fall is the pattern of the seasons.

An average is a way to squeeze many numbers into one. Add up thirty daily highs for January. Divide by thirty. That is January’s average high. The average hides the wild days. It shows the usual day instead.

Patterns let you predict. If January in Chicago averages about 32 °F, you can expect ice next January too. You cannot say which day will snow. But you can say winter coats will be needed. That is the difference between a single day and a pattern.

Here is a saying that helps. Weather is your mood. Climate is your personality. Weather is what the air does today. Climate is what the air usually does, measured over thirty years or more. A cold day in July does not change Chicago’s climate.

Scientists describe a climate with long-term averages. What is the usual January? The usual July? How much rain falls in a normal year? Illinois has cold winters, hot summers and rain in every season. A desert climate has very little rain at all.

Climate matters because living things and people plan around it. Farmers in Illinois plant corn in spring because the pattern says frost is over. Roofs here are built to hold snow. If a place’s climate slowly shifts, those plans have to shift too. Scientists track this with careful records.

Why is it snowing in Chicago while it is hot in Miami? Part of the answer is sunlight. Places near the equator get strong, direct sun all year. Places near the poles get weak, slanted sun. In between, like Illinois, the sun’s strength changes with the seasons.

Oceans and big lakes matter too. Water heats up and cools down slowly. A city by the sea has milder winters and cooler summers than a city far inland. Chicago’s lakefront is cooler on a hot day than a suburb 30 miles west. That is Lake Michigan at work.

Mountains block wet air. Rain falls on one side. The other side stays dry, a rain shadow. Seattle gets rain most of the year. Phoenix, in the desert, gets very little. Look at the numbers and you will see how different climates can be.

A tornado is a spinning tube of air that reaches from a thunderstorm down to the ground. Most last only minutes. But the wind inside can be faster than any car. Illinois sits where warm, wet air from the Gulf meets cold, dry air from the north. That clash builds the storms.

Illinois gets roughly 50 tornadoes in a typical year, most in spring and early summer. The worst in history was the Tri-State Tornado of March 18, 1925. It ran across Missouri, Illinois and Indiana. It killed about 695 people, the most of any single tornado in the United States.

Scientists rate tornadoes by their damage, using the Enhanced Fujita scale, from EF0 to EF5. A watch means the ingredients for a tornado are present. Stay alert. A warning means one has been spotted or seen on radar. Go to your safe place right away.

A flood happens when water covers land that is usually dry. Rivers spill over after days of rain. Streets fill when storm drains cannot keep up. Moving floodwater is the danger. Just 6 inches of fast water can knock an adult down. About 12 inches can float a car.

That is why the National Weather Service has a rule for drivers. If a road is covered, turn around. You cannot see how deep the water is. You cannot see if the road is still there underneath. Most flood deaths in the United States happen in vehicles.

A blizzard is not just heavy snow. It is snow with strong wind, at least 35 mph, that cuts what you can see to a quarter mile or less for three hours. Chicago’s great blizzard of January 1967 dropped about 23 inches. Cars and buses were buried on the roads.

Nobody can stop a tornado. But people can design for one. Storm shelters are small rooms with thick walls and heavy doors. Schools in tornado country practice drills so everyone knows the way to the inside hallway. Sirens and phone alerts give minutes of warning time.

Floods are fought with design too. Levees are long walls of earth along rivers. Chicago built huge tunnels deep underground, called the Deep Tunnel, to hold storm water until treatment plants can catch up. Homes in flood zones are sometimes lifted up on tall posts.

Every design has a cost and a trade-off. A levee protects one town but may push more water to the next. A shelter costs money. Engineers ask: what is the danger, how likely is it, and what is the best fix we can afford? That is engineering with weather in mind.

In 1743, Benjamin Franklin in Philadelphia wanted to see an eclipse. A storm blocked it. Later he learned the storm had hit Boston hours after it hit him, even though the wind had blown from the northeast. He figured out that storms travel as a whole, from one place to the next.

In 1803, an English chemist named Luke Howard gave clouds their names. Cumulus means heap: the puffy white ones. Stratus means layer: the flat gray sheet. Cirrus means curl: the thin high wisps. Those names are still used by every weather scientist today.

Clouds are clues. Tall, dark cumulus towers mean a thunderstorm is building. Thin cirrus often arrives a day before a rain system. A ring around the moon comes from ice crystals high up, and rain often follows. Watching the sky is real science when you write down what happens next.

Today’s forecasters have eyes everywhere. Weather radar sends out radio waves. Rain, snow and hail bounce them back. The radar draws a map of where precipitation is and which way it is moving. Doppler radar can even see wind spinning inside a storm, the start of a tornado.

Satellites circle Earth high above the clouds. They send pictures of storms across whole oceans. Twice a day, weather stations across the country release balloons that carry tiny instruments miles into the sky. They report temperature, wind and moisture all the way up.

All of that data flows into computers that solve the equations of moving air. The result is a forecast, a prediction of tomorrow’s weather. Forecasts a day ahead are usually right. A week ahead, they are less sure. Forecasters say ’a 40 percent chance of rain’ because the air does not always do what the model says.

Look at a road cut where a highway slices through a hill. You will often see stripes. Each stripe is a layer of rock. Layers form when mud, sand or tiny shells settle at the bottom of water and slowly harden. New layers pile on top of old ones.

That gives us a rule. In an undisturbed stack, the bottom layer is the oldest. The top layer is the youngest. It is like a pile of newspapers on a porch. The paper on the bottom was delivered first. Geologists, scientists who study rock, read a cliff from the bottom up.

Layers also tell what a place used to be. Sandstone made of tiny grains means an old beach or desert. Limestone full of shell pieces means a shallow warm sea. Much of Illinois sits on limestone. Long ago, this land was under a sea.

A fossil is the remains or mark of a living thing kept in rock. It might be a bone, a shell, a leaf print or a footprint. Fossils form when a dead plant or animal is buried fast in mud. It has to be buried before it rots. Over a very long time, the mud becomes rock. The shape stays.

Near Braidwood, southwest of Chicago, is Mazon Creek. About 300 million years ago it was a steamy swamp by the sea. Ferns as tall as trees grew there. Their buried remains became the coal Illinois still mines. Inside hard lumps of rock, collectors find leaves, insects and strange sea creatures.

The strangest is the Tully monster, found by a collector named Francis Tully in the 1950s. It had a long snout, eyes on stalks and a soft body. Nothing like it lives today. It is the Illinois state fossil. Fossils like this are evidence that life, and the land, has changed enormously.

In 1869, John Wesley Powell led nine men in wooden boats down the Colorado River. Nobody had mapped its canyons. Powell had lost an arm in the Civil War. He rode in a chair strapped to a boat and wrote notes about the rock walls rising around him.

The Grand Canyon in Arizona is about 277 miles long and more than a mile deep. Its walls are a stack of layers, oldest at the bottom. Powell saw that the river had cut down through all of them. Sand carried by fast water works like sandpaper on rock.

The lesson is time. A river cannot carve a mile of rock in a year, or a thousand years. It takes millions. The canyon is evidence that slow, steady change, given enough time, can do enormous work. Geologists call this ’deep time.’

Rock seems forever. It is not. Weathering is anything that breaks rock into smaller bits without moving it away. The biggest tool in Illinois is ice. Water seeps into a crack. At night it freezes. Ice takes up more room than water, so it pushes the crack wider.

Do it a hundred times and the rock splits. That is why Chicago streets grow potholes every spring. Water gets under the pavement, freezes, thaws and freezes again. Tree roots do the same thing more slowly. A root grows into a crack and pushes as it thickens.

Water also weathers rock by dissolving it. Rain is very slightly acidic. Limestone slowly melts away in it. Over ages this hollows out caves. Even sunlight helps. Rock heats and expands by day, cools and shrinks by night. Little by little, the surface crumbles.

Weathering breaks rock. Erosion moves the pieces somewhere else. Water is the champion mover. A creek after a storm runs brown because it is full of soil. Rivers carry sand and mud toward the sea. The faster the water, the bigger the pieces it can carry.

Wind erodes too, mostly in dry places. It lifts sand and dust and drops it far away. Dust from farm fields once blew all the way from Kansas to the East Coast in the 1930s. Gravity pulls loose rock downhill in landslides. Ice, as you read, drags whole boulders.

Plants slow erosion. Roots hold soil in place. Leaves soften the blow of rain. When a hillside is cleared, the next storm can wash it bare. Farmers in Illinois plant cover crops and leave old stalks on the field to keep the soil from blowing or washing away.

Everything that erodes has to land somewhere. Deposition is the dropping of rock bits and soil when water, wind or ice slows down. Fast water carries pebbles. Slow water can only carry the finest mud. So as a river slows, it drops the heavy stuff first.

Where a river meets the sea, it slows almost to a stop. It drops its load in a fan of mud called a delta. The Mississippi River has built a huge delta in Louisiana out of soil from Illinois, Iowa and a dozen other states. New land grows there year by year.

You can see deposition on a small scale. After a flood, a thin layer of mud coats the grass. Sandbars appear on the inside of a river bend, where the water is slowest. Wind drops sand into dunes at the Indiana Dunes, just around the lake from Chicago.

A landslide can move a hillside in a minute. A volcano can bury a town in a day. On May 18, 1980, Mount St. Helens in Washington exploded. The top 1,300 feet of the mountain was gone in minutes. Those are rapid changes. They are dramatic but rare.

Most change is slow. Niagara Falls has been wearing back its cliff for thousands of years, now at about a foot a year. The Grand Canyon took millions. In the 1780s, a Scottish farmer and doctor named James Hutton looked at rock layers and saw slow change everywhere.

Hutton argued that the same processes we see today made the land. Rain, rivers, ice and waves did the work, over unimaginable time. He wrote that he could find no sign of a beginning. He could find no sign of an end. The present is the key to the past. That idea is the heart of geology.

A glacier is ice so thick that it moves. Snow piles up faster than it melts, year after year. The weight squeezes the bottom into ice. Then the whole mass creeps downhill or spreads out, a few feet a year. It looks frozen still. Over decades, it flows.

Glaciers are bulldozers. The bottom of the ice is studded with rocks. As the ice slides, those rocks scratch and grind the ground beneath. They leave long scratches on bedrock that point the way the ice moved. The ice plucks boulders loose and carries them frozen inside.

During the last ice age, sheets of ice covered Canada and spread south. Ice reached almost 90 percent of Illinois at one time or another. It went farther south here than anywhere else in North America, close to Carbondale. The ice finally melted out of Illinois roughly 14,000 years ago.

When a glacier melts, it drops everything it carried. That jumbled mix of clay, sand, gravel and boulders is called till. Till covers most of Illinois, in places more than 100 feet deep. It buried the old hills and valleys. That is the flat land you see.

Sometimes the ice edge stood still for a while. Then till piled up in a long ridge called a moraine. Northeast Illinois has many of them. They are low hills curving around the south end of Lake Michigan. The lake itself sits in a basin the ice scooped out. Meltwater filled it.

The ice gave Illinois something else: some of the best farm soil on Earth. Wind picked up fine dust from the melting glacier’s outwash and spread it across the state. Ground-up rock is full of minerals plants need. Prairie grass grew, died and rotted into it for thousands of years.

Put every earthquake of the last fifty years on a world map. They do not spread out evenly. They cluster in long, narrow belts. A giant belt circles the Pacific Ocean, through Japan, Alaska, California and Chile. Volcanoes line up in the same belt. It is called the Ring of Fire.

The pattern is evidence. Earth’s outer shell is broken into huge slabs called plates. They creep about as fast as your fingernails grow. Where they push, pull or grind against each other, rock breaks and shakes. Melted rock rises. That is why the belts exist.

Illinois is far from any plate edge, but not safe from shaking. In the winter of 1811 and 1812, huge earthquakes near New Madrid, Missouri, cracked the ground in southern Illinois. Reports say the Mississippi River briefly ran backward. Small quakes still rattle that area.

The first tool is a map. If earthquakes cluster in belts, builders know where to be careful. In California, buildings are made to sway instead of snap. Steel frames bend. Heavy water tanks are strapped down. In Japan, some towers sit on rubber pads that soak up shaking.

Rivers have patterns too. A floodplain is the flat land beside a river that floods every so often. Maps show which land floods often. Some towns keep floodplains as parks and farms, not houses. Others build levees or raise homes on posts.

Every choice is a trade-off. Stronger buildings cost more. Leaving a floodplain empty means less land for homes. Engineers and towns weigh the danger, how often it comes, and what they can afford. Knowing the pattern is what makes the choice possible.

The sun is a star. That may sound odd, because it does not look like the tiny sparks in the night sky. But it is the same kind of thing. It is a giant ball of hot gas that makes its own light. The night stars are suns too, unimaginably far away.

The sun is close, as stars go. It is about 93 million miles from Earth. Light is the fastest thing there is, and it still takes about 8 minutes to make the trip. When you feel sunlight on your face, it left the sun 8 minutes ago.

The sun is also enormous. About 109 Earths could line up across its middle. It looks small because it is far away, the way a jet looks like a speck when it is miles up. Never look straight at the sun. Its light is strong enough to hurt your eyes for good.

Look up on a clear night. Some stars are bright. Some you can barely see. Two things decide that. One is how much light the star really gives off. The other is distance. A bright star far away can look dimmer than a weak star nearby.

Star distances are so big that miles stop being useful. Astronomers use the light-year, the distance light travels in one year. That is about 6 trillion miles. The nearest star after the sun, Proxima Centauri, is about 4 light-years away. Its light left it four years ago.

Sirius, the brightest star in the night sky, is about 8.6 light-years away. Some stars you can see are hundreds of light-years off. Their light left them before your grandparents were born. Looking at stars is looking back in time.

Stars do not move around compared to each other. The same groups appear in the same shapes year after year. People long ago connected them into pictures and gave them names. Those groups are constellations. The Big Dipper, with its seven bright stars, is one part of a larger one.

The Big Dipper is a good starting point in Illinois. It can be seen on any clear night of the year. Follow the two stars at the end of its bowl and you reach Polaris, the North Star. Polaris sits almost straight above Earth’s North Pole, so it always marks north.

Sailors and travelers steered by Polaris for centuries. Before compasses, before maps, the stars were the map. Once you learn a few constellations, the night sky stops being random dots. It becomes a place with landmarks, and you can find your way in it.

Earth is a ball spinning in space. It turns all the way around once every 24 hours. That spin is called rotation. Earth rotates around an imaginary line through the North and South Poles, its axis. You cannot feel the spin because everything around you spins with you.

Half of Earth always faces the sun. That half has day. The other half faces away, into dark space. That half has night. As Earth turns, your town swings from the dark side into the lit side. That is sunrise. Later it swings back into the dark. That is sunset.

It is tempting to say the sun goes around Earth. It looks that way. But if the sun moved and Earth sat still, the stars would have to circle us every day too, and so would the moon, all at the same speed. One spinning Earth explains everything at once. That is why scientists trust it.

Earth spins toward the east. So the sun seems to come up in the east. It climbs higher through the morning. In Illinois, it is never straight overhead. At noon it is highest, and it stands in the southern half of the sky. Then it sinks and sets in the west.

That path is why south-facing windows get the most sun. It is why a sidewalk on the north side of a building stays icy longest. It is why the noon shadow of a stick points north. The sun is to the south, so the shadow falls the other way.

The path changes a little with the seasons. In summer the sun rises in the northeast and climbs very high. In winter it rises in the southeast and stays low. But east to west, low to high to low, is the same every single day. It is one of the most reliable patterns on Earth.

A shadow is the dark spot where something blocks the light. Your shadow stretches away from the sun. When the sun is low, near the horizon, shadows are long. When the sun is high, shadows are short. That is the whole rule, and it makes a shadow a clock.

In the morning the sun is low in the east. Shadows are long and point west. By noon the sun is high in the south. Shadows are short and point north. In the afternoon the sun sinks toward the west. Shadows grow long again, pointing east.

People used this for thousands of years. A sundial is just a stick and a set of marks. Record the shadow every hour for one day. Then the marks tell time on any sunny day. You can also check the pattern. It repeats, day after day, with tiny changes through the year.

Earth travels around the sun once a year. That trip is its orbit. Earth’s axis is tilted, about 23.5 degrees, and the tilt always points the same way in space. For part of the year the northern half leans toward the sun. For the other part it leans away.

When Illinois leans toward the sun, the sun climbs high and days are long. Sunlight hits the ground more directly and heats it more. That is summer. Chicago gets about 15 hours of daylight in late June. When Illinois leans away, the sun stays low and days are short, about 9 hours in late December. That is winter.

Many people think summer happens because Earth is closer to the sun. It is not true. Earth is actually a little closer to the sun in January. The tilt is what matters. That is also why Australia has summer while Illinois has winter. The southern half is leaning toward the sun then.

Orion, the hunter with three stars in a row for a belt, rules the winter sky in Illinois. By July, it is gone. In its place, near the southern horizon, the curled tail of Scorpius appears. Then Orion comes back in December. The stars did not move. Earth did.

Night is the side of Earth facing away from the sun. As Earth goes around its orbit, that dark side points at a different part of space each season. In winter it points toward Orion. In summer it points the other way, toward Scorpius. Orion is still there in summer, but it is up during the day, lost in sunlight.

Some stars never leave. The Big Dipper and Polaris sit near the direction of Earth’s axis. So they are visible all year from Illinois. Watching which constellations come and go is another pattern. This one takes a whole year to repeat.

The moon does not make its own light. It reflects sunlight. Half of the moon is always lit by the sun, just as half of Earth is. What changes is how much of that lit half we can see. The shapes we see are the phases of the moon.

The moon orbits Earth about once a month. When it is between Earth and the sun, its lit side faces away from us. We see nothing: a new moon. A week later we see half of it: first quarter. Two weeks in, the whole lit side faces us: full moon. Then it shrinks back.

The whole cycle takes about 29.5 days. In 1610, Galileo pointed one of the first telescopes at the moon. He saw mountains and craters, not a smooth glowing disk. He measured the mountains from their shadows. The moon was a world, with ground you could stand on.

Drop a ball. It falls. Drop it in Chicago, in Australia, or at the South Pole. It falls toward the ground every time. Gravity is the pull that draws everything toward the center of Earth. On a round planet, ’down’ means toward the middle, wherever you stand.

That is why people in Australia do not fall off. Their ’down’ points toward Earth’s center too, just like yours. Gravity also holds the air close to Earth and keeps the moon circling us. It is the same pull, everywhere, all the time.

In July 1969, Apollo 11 astronauts landed on the moon. The moon’s gravity is about one sixth as strong as Earth’s, so they bounced in slow hops. But they did not float away. The moon pulled them toward its center, just as Earth pulls you. Gravity works on every world.

Stand on a beach. Under your feet is sand and, below that, rock. That is the geosphere, all of Earth’s rock and soil, from mountains to the hot center. In front of you is water. That is the hydrosphere: oceans, lakes, rivers, ice, and water underground.

Over your head is air. That is the atmosphere, the blanket of gases wrapped around Earth. And the gulls, the seaweed, the crabs, and you are the biosphere: every living thing on the planet. Four systems, and you are standing in all of them at once.

Scientists split Earth into these four parts to study them. But the parts are never really separate. Rain from the atmosphere falls on the geosphere and joins the hydrosphere. A plant drinks it. The trick to understanding Earth is watching how the four spheres act on each other.

Watch the wind on Lake Michigan. Moving air (atmosphere) pushes the water (hydrosphere) into waves. The waves pound the shore and grind rock into sand (geosphere). Beach grass (biosphere) takes root in that sand and holds it against the next storm. Four spheres, one beach.

Living things are surprising movers. Tree roots crack rock. Earthworms turn soil. Tiny ocean creatures build shells that pile into limestone. Plants take carbon dioxide out of the air and put oxygen back. Over billions of years, life has changed the whole atmosphere.

The naturalist John Muir put it simply, more than a century ago. Try to pick out anything by itself, he wrote, and you find it hitched to everything else. That is the big idea of Earth science. Change one sphere and you change the others.

Air is not one thing. It is a mix of gases. About 78 percent is nitrogen, which does very little in your body. About 21 percent is oxygen, the part you need with every breath. Less than 1 percent is everything else, including carbon dioxide, the gas plants use to grow.

The atmosphere seems endless, but it is thin. Most of the air sits in the bottom 10 miles. Jets fly near the top of that. Compared with the whole Earth, the atmosphere is like the skin on an apple. It is that thin, and it is all we have.

That thin layer does a lot. It holds in warmth at night so Earth does not freeze. It blocks the sun’s most harmful rays. It carries water from the ocean to the land as rain. And it moves. Wind is the atmosphere on the go, mixing warm and cold air across the planet.

From space, Earth is blue. Oceans cover about 70 percent of its surface. If you added up all the water on the planet, about 97 percent of it would be salt water in the seas. You cannot drink it. Crops cannot grow with it. It would take a huge amount of energy to remove the salt.

The other 3 percent is fresh water. That sounds small, and it is. Most of it is locked away too. About two thirds of the fresh water is frozen in ice sheets and glaciers in Antarctica and Greenland. Most of the rest is underground, in the tiny spaces between grains of rock and soil.

Lakes and rivers are the water you can see. They hold only a sliver of Earth’s fresh water. Yet that sliver is what most people and animals drink. A graph of Earth’s water is a lesson. It shows how precious the drinkable part is.

Dig a hole in wet ground and it slowly fills with water. That water was already there, in the tiny gaps between soil grains and in cracks in rock. It is groundwater. Rain and melting snow soak down into the ground and fill those spaces from the bottom up.

The top of the water-filled zone is the water table. A well is just a pipe drilled below it. Many Illinois towns far from Lake Michigan drink groundwater. Farmers pump it for crops. Springs are places where the water table meets the surface and water flows out on its own.

Groundwater moves very slowly, sometimes only a few feet a year. That means it refills slowly too. Pump out more than the rain puts back and the water table drops. Wells go dry. Spill chemicals on the ground and they can reach the groundwater and stay for decades.

Chicago sits beside one of the largest supplies of fresh water on Earth. There are five Great Lakes. Together they hold about one fifth of the world’s surface fresh water. Lake Michigan is the only one that lies entirely inside the United States.

Chicago’s drinking water comes from the lake. Pipes reach out to intake cribs about 2 miles from shore. Water is pumped to treatment plants, cleaned, and sent through thousands of miles of pipe to homes in the city and many suburbs. Turn on a tap and you are drinking the lake.

The lake gives, but it also needs protection. Waste, road salt and fertilizer washed from streets and farms all end up there. Rules now limit what can go in, and the water is far cleaner than it was in 1900. Keeping it that way is a job that never ends.

The story that opened this chapter is a lesson in systems. Chicago’s waste went into the river (hydrosphere). The river went into the lake. The lake was the drinking water. Sick people (biosphere) were the result. The problem ran through every sphere.

The fix was to dig. The Sanitary and Ship Canal, opened in January 1900, was deep enough that water flowed out of the lake and into the canal. The river’s direction reversed. Waste now traveled southwest, toward the Illinois River and the Mississippi.

Chicago’s drinking water got safer. But towns along the Illinois River got the waste. Later, Chicago built treatment plants to clean the water before it left the city. Today the city also has the Deep Tunnel, more than 100 miles of huge tunnels that hold storm water until plants can clean it.

Everything you own came from Earth. Your desk was a tree. Your phone holds metals dug from rock. The lights run on electricity, much of it made by burning coal or gas pulled from underground. These are natural resources: things from Earth that people use.

Illinois is rich in resources. Its deep black soil grows more corn and soybeans than almost any state. Coal lies under much of the southern half. Rivers and the lake carry ships. But using resources changes the land. When settlers arrived, tall prairie grass covered most of Illinois. Today only tiny scraps of that prairie remain.

Some resources grow back. Trees, crops and clean water are renewable if we do not use them faster than they return. Coal, oil and metals do not grow back on any human timescale. They are nonrenewable. Once burned or used, they are gone. That difference shapes how carefully each should be used.

Every can, bottle and box takes resources to make and energy to move. When it is thrown away, it goes to a landfill, a giant pit that is covered when full. Landfills take up land and can leak into groundwater. Three habits shrink what goes there: reduce, reuse, recycle.

Reduce means use less in the first place: a refillable bottle instead of a new one each day. Reuse means use the same thing again: a jar becomes a pencil cup. Recycle means send the material back to a factory to become something new. Old paper becomes new paper. Old cans become new cans.

Recycling saves more than space. Making a can from recycled aluminum uses about 95 percent less energy than making one from raw ore. But recycling is not free either. Trucks, sorting and cleaning all take energy. That is why ’reduce’ comes first on the list.

People change Earth, but people can also protect it. In 1970, millions of Americans marked the first Earth Day. Soon after, laws limited what factories could put into rivers and the air. Rivers that once caught fire from pollution now have fish again. Chicago’s river is one of them.

Illinois groups are bringing back the prairie. They collect seeds from surviving patches and plant them on old fields and along highways. Deep roots return. Butterflies and birds follow. It takes years, but a piece of the biosphere that was almost gone is growing back.

Protecting Earth’s systems is not about stopping all use. People need food, water, energy and homes. It is about stewardship: using resources wisely so they last, measuring the effects, and fixing problems when the evidence shows them. Every one of the four spheres is in your care.