Nature & Earth: Living Things and Rocks
Living things solve hard engineering problems every day: breathing underwater, navigating thousands of kilometres, climbing glass. The planet itself is slowly rebuilt by heat, pressure and water.
These explainers cover both: how animals and plants do what they do, and how rocks, soil, mountains and gems are made.
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How does natural selection work?
Natural selection works because individuals with traits better suited to their environment tend to survive and reproduce more. Those helpful traits get passed on, so over many generations a population gradually adapts — the engine of evolution.
How do birds fly?
Birds fly by using the special shape of their wings to create lift. Air moving over the curved top of a wing travels faster, lowering pressure above it, so higher pressure below pushes the bird up. Flapping provides thrust to move forward.
How does echolocation work?
Echolocation works by sending out sound pulses and listening for the echoes that bounce back. By timing how long each echo takes and how it changes, an animal like a bat or dolphin builds a precise sound 'picture' of the objects around it in the dark.
Every explainer in this guide · 75
How does bioluminescence work?
Bioluminescence is light produced by living things, like fireflies and deep-sea creatures, through a chemical reaction inside their bodies. A light-emitting molecule reacts with oxygen, releasing energy almost entirely as light rather than heat.
How do leaves change color in autumn?
Leaves change color in autumn because trees stop making chlorophyll, the green pigment used for photosynthesis. As the green fades, yellow and orange pigments that were always there get revealed, while reds are made fresh — before the leaves fall.
How does photosynthesis work?
Photosynthesis works in two stages: light-dependent reactions capture sunlight in the chloroplasts to make energy carriers, then the Calvin cycle uses that energy to turn carbon dioxide and water into glucose, releasing oxygen.
How do plants grow?
Plants grow by making their own food through photosynthesis and pulling water and minerals from the soil. Using sunlight, water, and carbon dioxide, they build sugars for energy and new tissue, growing roots down and stems and leaves up.
How do tectonic plates move?
Tectonic plates are huge slabs of Earth's crust that float on the hot, slowly flowing rock beneath. Heat from deep inside Earth drives convection currents in that rock, dragging the plates a few centimeters a year — building mountains and causing earthquakes.
How does an earthquake happen?
An earthquake happens when stress built up in the Earth's crust is suddenly released, usually as two tectonic plates slip past each other along a fault. That sudden movement sends out waves of energy that shake the ground.
How does a volcano work?
A volcano works as an opening in Earth's crust where molten rock, ash, and gas escape from below. Deep heat melts rock into magma, which is lighter than the solid rock around it, so it rises and erupts at the surface as lava.
How does the rock cycle work?
The rock cycle is the slow, continuous process by which rocks change from one type to another over millions of years. Heat, pressure, melting, weathering, and sediment build-up keep recycling Earth's rock between igneous, sedimentary, and metamorphic forms.
How does a fossil form?
A fossil forms when the remains or traces of a once-living thing are preserved in rock over thousands to millions of years. Usually, minerals slowly replace buried bone or shell, turning it to stone and capturing a record of ancient life.
How does a coral reef form?
A coral reef works as a living structure built by tiny animals called coral polyps, which secrete hard skeletons that pile up over centuries. Living coral relies on algae inside it for food, creating a vibrant ecosystem that shelters a quarter of marine life.
How does a pearl form?
A pearl works as an oyster's defense: when an irritant slips inside its shell, the oyster coats it in layer after layer of the same smooth material that lines the shell. Over years, these layers build up into a lustrous pearl.
How does carbon dating work?
Carbon dating measures the age of once-living things by tracking radioactive carbon-14. Living organisms absorb carbon-14, which then decays at a steady, known rate after death. By measuring how much is left, scientists estimate how long ago it died.
How do caves form?
Caves form when slightly acidic water seeps through cracks in soluble rock like limestone, dissolving the rock over thousands of years to create underground voids. This process, called dissolution, gradually enlarges fissures into tunnels and chambers.
How do sand dunes form?
Sand dunes form when wind carries loose sand grains across a surface until an obstacle or rough patch slows the wind and forces the grains to drop. The pile grows into a mound, and the wind keeps reshaping it into the familiar dune shape with a gentle windward slope and a steep leeward slip face.
How does a landslide happen?
A landslide happens when gravity overcomes the friction holding a slope's material in place, causing rock, soil, or debris to move downhill. This usually follows heavy rain, earthquakes, or human excavation that weaken the slope's stability.
How do bees make honey?
Bees make honey by collecting nectar from flowers, adding enzymes to convert sucrose into simpler sugars, and then fanning the nectar to evaporate water until it becomes thick and stable. The final product is stored in wax cells as a long-lasting energy source for the colony.
How do birds migrate?
Birds migrate by using innate compasses—the sun, stars, and Earth's magnetic field—to navigate between seasonal homes. They build fat reserves and may fly thousands of kilometres, often in flocks, to reach food or breeding grounds.
How do fish breathe underwater?
Fish breathe underwater by extracting dissolved oxygen from water using gills. Water flows in through the mouth and out over the gills, where oxygen enters the blood and carbon dioxide is released.
How do plants absorb water?
Plants absorb water mainly through root hairs, which are tiny extensions of root epidermal cells that increase surface area for osmosis. Water then moves through the root cortex to the xylem and is transported upward to the leaves by transpiration pull.
How do seeds germinate?
Germination begins when a seed absorbs water, which swells the seed and activates enzymes that break down stored food into energy. The embryo then uses this energy to grow a root and shoot, emerging as a seedling.
How do chameleons change color?
Chameleons change colour by adjusting their skin cells: a lattice of tiny crystals in cells called iridophores is spaced closer or wider to reflect different colours, while pigment cells add yellows, reds and darker tones. They use these shifts mainly for signalling and temperature control.
How do cats purr?
Cats purr when the brain sends signals to the muscles of the larynx and diaphragm, causing them to vibrate at a steady rate. This vibration, combined with airflow from the lungs, produces the purring sound.
How do spiders make silk?
Spiders make silk by pulling a liquid protein solution through microscopic spigots on their abdomen, where it solidifies into a fibre as it is stretched. The silk is stored as a liquid gel inside glands and only becomes solid thread outside the body.
How do geckos climb walls?
Geckos climb smooth vertical surfaces using millions of microscopic hairs on their toe pads that create weak electrical attractions called van der Waals forces with the surface. These forces act only at extremely close range, so the toes must make intimate contact, and geckos peel their feet off step by step to detach.
How does a caterpillar become a butterfly?
A caterpillar becomes a butterfly through metamorphosis, a process where it forms a chrysalis and its body is rebuilt. Inside, most larval tissues dissolve and are reorganized into adult structures like wings and antennae.
How do mushrooms grow?
Mushrooms grow from spores that germinate into thread-like hyphae, which fuse to form a network called mycelium. When conditions are right, the mycelium produces a fruiting body—the mushroom—that releases new spores to repeat the cycle.
How do diamonds form?
Diamonds form when carbon is subjected to extreme pressure and high temperature deep within Earth's mantle, typically 150 to 250 kilometers below the surface. The carbon atoms crystallize into a cubic lattice, and the diamonds are later brought to the surface by volcanic eruptions.
How does coal form?
Coal forms when dead plant material accumulates in swamps, is buried under sediment, and is slowly transformed by heat and pressure over millions of years. This process, called coalification, concentrates carbon and drives off water and gases, turning peat into lignite, then bituminous coal, and finally anthracite.
How does crude oil form?
Crude oil forms when tiny marine organisms die and settle on oxygen-poor sea floors, where heat and pressure over millions of years transform their remains into liquid hydrocarbons. This process, called diagenesis and catagenesis, occurs at depths of 1 to 4 kilometers and temperatures between 60°C and 150°C.
How do islands form?
Islands form when tectonic forces lift the seafloor above water, or when volcanoes erupt and build new land, or when corals and sediments accumulate in shallow seas. They can also appear when sea levels drop and expose high ground that was previously submerged.
How does soil form?
Soil forms when weathered rock fragments mix with decayed plant and animal matter over long periods. Living organisms, water, and air slowly transform this mixture into a structured, fertile material that supports plant life.
How do crystals grow?
Crystals grow when atoms or molecules in a liquid or gas arrange themselves into an ordered, repeating pattern called a crystal lattice. This happens when the solution becomes supersaturated or the melt cools below its freezing point, forcing particles to deposit onto a tiny seed crystal.
How do stalactites form?
Stalactites form when water dripping from a cave ceiling deposits dissolved calcium carbonate. Each drop leaves behind a tiny ring of calcite, and over thousands of years these rings grow downward into icicle-shaped formations.
How do mountains form?
Mountains form when tectonic plates collide, causing the crust to crumple and thicken, or when volcanic activity builds up rock. Erosion then sculpts these uplifted regions into peaks and valleys.
How does gold form?
Gold forms when neutron stars collide or massive stars explode, forging heavy elements that are scattered into space and later concentrated into veins by hot fluids in Earth's crust. Most gold on Earth sank to the core when the planet was molten, so mineable deposits come from later asteroid impacts and geological recycling.
How does natural gas form?
Natural gas forms when buried organic matter is heated underground over millions of years, breaking large molecules into smaller hydrocarbon gases. Most of it is methane, produced either by heat-driven cracking or by microbes in shallow sediments.
How does a supervolcano work?
A supervolcano works when a vast magma reservoir beneath the crust builds up so much gas-rich molten rock that the overlying ground can no longer contain the pressure, and the crust collapses into the emptied chamber. This produces an eruption thousands of times larger than an ordinary volcano, leaving a wide caldera rather than a tall cone.
How does coral bleaching happen?
Coral bleaching happens when heat stress makes corals expel the algae living in their tissues, which supply most of their colour and food. Without these algae, the coral turns white and, if the stress continues, can starve and die.
How do dolphins sleep?
Dolphins sleep with one brain hemisphere at a time, keeping the other awake to control breathing and watch for danger. This unihemispheric slow-wave sleep lets them rest for hours while staying partly conscious and able to swim.
How do electric eels make electricity?
Electric eels generate electricity using specialised cells called electrocytes, which are stacked in series like batteries. When a signal from the brain triggers them, ions flow across each cell's membrane, adding up to a powerful discharge.
How does regeneration work in animals?
Regeneration works when specialised cells at a wound site dedifferentiate into a mass called a blastema, then multiply and reorganise into the missing body parts. The extent of regrowth depends on the animal: some replace whole limbs, while humans mostly repair tissue with scar.
How do snakes shed their skin?
Snakes shed their skin through a process called ecdysis, where a new layer of skin forms underneath the old one. The old skin then loosens and peels off, usually in one piece, as the snake rubs against rough surfaces.
How does a fjord form?
A fjord forms when a glacier carves a deep U-shaped valley below sea level and the sea floods it after the ice retreats. The steep walls and drowned valley create the narrow, deep inlets seen along coasts like Norway.
How does a canyon form?
A canyon forms when a river cuts down into rock faster than the valley sides can wear back, slicing a deep, steep-walled gorge over hundreds of thousands to millions of years. Uplift of the land often speeds the cutting, while rockfalls and weathering slowly widen the walls.
How does an oxbow lake form?
An oxbow lake forms when a looping river bend is cut off from the main channel, leaving a curved, U-shaped lake beside the river. Erosion on the outside of bends and deposition on the inside slowly squeeze a meander's neck until floodwater breaks through and sediment seals the old loop.
How does a beach form?
A beach forms where waves drop loose sediment such as sand, pebbles or shell fragments along the edge of the sea or a lake. Rivers, eroding cliffs and broken shells supply the material, and the balance between waves that build up the shore and waves that strip it away shapes the beach.
How does an atoll form?
An atoll forms when a coral reef grows around a volcanic island that slowly sinks, so the reef keeps building upward while the island disappears beneath the sea. What remains is a ring of coral reef and low sandy islands surrounding a shallow central lagoon.
How does a geode form?
A geode forms when a hollow space inside rock slowly fills from the walls inward with minerals carried by groundwater, leaving crystals pointing toward a cavity in the middle. The hollow may start as a gas bubble in lava or a dissolved lump in sedimentary rock, and the crystals take thousands of years or longer to grow.
How does ocean acidification work?
Ocean acidification happens when seawater absorbs carbon dioxide from the air, which reacts with water to form carbonic acid and lowers the ocean's pH. That chemistry also removes carbonate ions that corals, oysters and other shell-builders need, making it harder for them to build and maintain their skeletons.
How does camouflage work in animals?
Animal camouflage works by making an animal hard to see or recognise, using colours, patterns, shapes and behaviour that blend it into its surroundings or disguise it as something else. Natural selection favours these traits because prey that go unnoticed survive, and predators that stay hidden catch more food.
How does hibernation work?
Hibernation works by sharply slowing an animal's metabolism so that its body temperature, heart rate and breathing fall far below normal, letting it survive cold months on stored fat. Shortening days and falling temperatures trigger the change, and the animal rewarms periodically using heat from special brown fat.
How does snake venom work?
Snake venom works as a mixture of proteins and enzymes, produced in modified salivary glands and injected through fangs, that attacks specific systems in the victim's body. Depending on the species, its toxins can paralyse nerves and muscles, disrupt blood clotting, or destroy tissue around the bite.
How do ant colonies work?
An ant colony works as a cooperative family in which one or more queens lay eggs while thousands of sterile female workers find food, raise young and defend the nest. No single ant gives orders; chemical signals called pheromones and simple individual rules add up to organised colony-wide behaviour.
How do termites build their mounds?
Termites build their mounds by mixing soil with saliva and droppings into small pellets, which workers stack into walls, tunnels and chimneys around the colony's underground nest. The finished mound acts like a lung, using daily temperature swings and wind to move air through porous walls, exchanging gases for the colony.
How do whales breathe?
Whales breathe air through blowholes on top of their heads, surfacing to exhale and inhale in a quick burst before diving again. They store oxygen in blood and muscle, slow their heart and limit blood flow to non-essential organs, which lets some species stay underwater for an hour or longer.
How do jellyfish sting?
Jellyfish sting by firing thousands of microscopic venom capsules, called nematocysts, from cells lining their tentacles when something brushes against them. Each capsule bursts open under high internal pressure, shooting a coiled hollow thread into the skin and pumping venom through it in a fraction of a millisecond.
How do cats always land on their feet?
Cats land on their feet by using the righting reflex: their inner ear senses which way is down, and their flexible spine lets them twist the front and back halves of the body separately. By tucking and extending legs in turn, a falling cat rotates upright without anything to push against.
How do parrots talk?
Parrots talk by copying sounds they hear with a voice organ called the syrinx, located where the windpipe splits toward the lungs, rather than with vocal cords. Their thick, muscular tongue and beak then shape that sound, while specialised brain circuits let them learn and repeat new noises throughout life.
How do camels survive without water?
Camels survive without water by losing very little of it: their kidneys make concentrated urine, their dung is dry, their noses reclaim moisture from breath, and their body temperature rises during the day instead of sweating. When water appears, they can drink an enormous volume in minutes to refill.
How do penguins stay warm?
Penguins stay warm by trapping heat with densely packed, overlapping feathers, a thick layer of fat beneath the skin and blood vessels that recycle heat before it reaches their feet and flippers. In the harshest cold, emperor penguins also huddle in large groups to share body warmth.
How do fish float?
Most bony fish float at a chosen depth using a swim bladder, a gas-filled sac whose volume they adjust so their overall density matches the surrounding water. Fish without a swim bladder, such as sharks, rely instead on oily livers and the lift from swimming to avoid sinking.
How do insects fly?
Insects fly by flapping thin, rigid wings with powerful flight muscles in the thorax, often hundreds of times a second, while twisting each wing on every stroke. That twisting creates a swirling vortex along the wing's front edge, which generates far more lift than a fixed aeroplane wing would.
How does a Venus flytrap work?
A Venus flytrap catches prey with hinged leaf lobes that snap shut when an insect touches the sensitive trigger hairs inside twice in quick succession. Electrical signals then make the curved lobes flip shape in about a tenth of a second, and the sealed trap digests the insect over several days.
How do sunflowers follow the sun?
Young sunflowers follow the sun because the stem grows unevenly: during the day the east side lengthens faster, tilting the bud westward, and at night the west side grows faster, swinging it back east. An internal circadian clock times this growth, and mature flower heads stop moving and face east.
How do tree rings form?
Tree rings form because a thin layer of dividing cells under the bark, the cambium, adds new wood each growing season, making large pale cells in spring and small dense dark cells later in the year. Each pale-and-dark pair marks one year's growth, so counting them reveals a tree's age.
How do seeds spread?
Seeds spread through wind, water, animals and the plant's own force, each carrying them away from the parent so seedlings avoid competing for light, water and nutrients. Plants shape their seeds and fruits to suit one method, from feathery parachutes and floating husks to sweet fruits and hooked burrs.
How do cacti store water?
Cacti store water in thick, fleshy stems packed with spongy tissue whose cells and gel-like mucilage soak up and hold moisture after rain. Pleated ribs let the stem swell and shrink like an accordion, while waxy skin, spines instead of leaves and night-time gas exchange keep that stored water from escaping.
How does mold grow?
Mold grows when microscopic fungal spores land on damp organic material, absorb moisture and sprout thread-like hyphae that spread through the surface. The hyphae release enzymes that digest the material outside the fungus, absorb the nutrients, and then raise stalks that release new spores into the air.
How are GMO crops made?
GMO crops are made by inserting a specific gene, often from another organism, into a plant cell's DNA so the plant gains a new trait such as pest resistance. Scientists then grow a whole plant from that modified cell, test it extensively and breed the trait into high-yielding varieties.
How does hydroponics work?
Hydroponics grows plants without soil by bathing their roots in water that carries every mineral nutrient the plant needs. Pumps, air stones and inert supports such as coco coir or clay pebbles replace the jobs soil normally does, delivering water, food and oxygen directly to the roots.
How do fertilizers work?
Fertilizers work by adding mineral nutrients, chiefly nitrogen, phosphorus and potassium, that plants absorb through their roots to build proteins, DNA and chlorophyll. They replace what earlier harvests removed from the soil, letting crops grow faster and yield more than the soil could support alone.
How does drip irrigation work?
Drip irrigation works by pushing water through a network of pipes and small emitters that release it slowly, drop by drop, at the base of each plant. Because water goes straight to the root zone, far less is lost to evaporation, runoff or watering bare ground between rows.
Key ideas behind them
What is evolution?
Evolution is the process by which living things change across generations as heritable traits become more or less common. Driven mainly by natural selection, it explains the diversity of life and how species adapt to their environments.
What is plate tectonics?
Plate tectonics is the theory that Earth's rigid outer shell is broken into large plates that slowly move on the hotter, softer mantle beneath. Their motion builds mountains, opens oceans, and causes most earthquakes and volcanoes.
What is symbiosis?
Symbiosis is a close, long-term relationship between two different species. It can benefit both (mutualism), benefit one without harming the other (commensalism), or benefit one at the other's expense (parasitism) — shaping ecosystems everywhere.
What is a keystone species?
A keystone species is one whose presence holds an entire ecosystem together, far out of proportion to its numbers. Remove it and the whole web of life can unravel — like pulling the keystone from a stone arch.
What is pollination?
Pollination is how flowering plants reproduce: pollen is carried from one flower to another, fertilizing it so it can make seeds and fruit. Bees, other animals, wind, and water do the carrying — making pollination vital for food and ecosystems.
What is a food chain?
A food chain shows how energy and nutrients pass from one living thing to another as they eat and are eaten. It starts with producers (like plants), moves to consumers (animals), and ends with decomposers that recycle everything.
What is biodiversity?
Biodiversity is the variety of all living things — the range of species, the genetic differences within them, and the ecosystems they form. High biodiversity keeps nature resilient and supports the food, water, and air we depend on.
What is an ecosystem?
An ecosystem is a community of living things — plants, animals, and microbes — interacting with each other and with their non-living surroundings like air, water, soil, and sunlight. Energy and nutrients flow through it, linking every organism into one interdependent system.
What is a rock?
A rock is a naturally occurring solid made of one or more minerals. Rocks form the solid outer layer of the Earth, and they're grouped into three main types — igneous, sedimentary, and metamorphic — based on how they formed.
What is a mineral?
A mineral is a naturally occurring, solid substance with a specific chemical composition and an orderly internal crystal structure. Minerals are the building blocks of rocks — quartz, feldspar, diamond, and gold are all minerals.
What is igneous rock?
Igneous rock is rock that forms when molten rock — magma or lava — cools and hardens. It's one of the three main rock types. Granite (cooled slowly underground) and basalt (cooled quickly at the surface) are common examples.
What is sedimentary rock?
Sedimentary rock forms when layers of sediment — bits of sand, mud, shells, and other material — pile up and are compressed and cemented together over long periods. It's one of the three main rock types, and it's where most fossils are found.
What is metamorphic rock?
Metamorphic rock forms when an existing rock is transformed by intense heat and pressure deep underground — without fully melting. The word means 'changed form'. Marble (from limestone) and slate (from shale) are common examples.
हिंदी में पढ़ें: प्राकृतिक चयन (natural selection) कैसे काम करता है? · पक्षी कैसे उड़ते हैं? · इकोलोकेशन कैसे काम करता है? · बायोलुमिनेसेंस कैसे काम करता है? · पतझड़ में पत्तों का रंग कैसे बदलता है? · प्रकाश संश्लेषण कैसे काम करता है? · पौधे कैसे बढ़ते हैं? · टेक्टोनिक प्लेटें कैसे चलती हैं?
Frequently asked questions
How do animals know where to migrate?
Many use several cues at once: the Sun's position, star patterns, Earth's magnetic field, landmarks and smells. Some of this is inborn, and some is learned from older animals.
How long does it take for rocks to form?
It varies enormously. Volcanic rock can solidify in days to years, while sedimentary and metamorphic rocks usually take thousands to millions of years.
Why do leaves change colour in autumn?
Trees stop making green chlorophyll as days shorten, revealing yellow and orange pigments that were there all along; some trees also make new red pigments.