The wonder of science: curated ideas

About this collection

Where to begin.

Begin with the human body, then explore the natural world and discoveries in physics.

DriveMind

Neuroplasticity is the brain's ability to change its connections, and even its structure, in response to experience. It is strongest in childhood but continues through adult life, which is why adults can still learn a language, an instrument or a new skill, even if it often takes them longer.

For much of the 20th century scientists believed the adult brain was more or less fixed. Brain scans changed that view. In 2004 researchers in Germany taught adults to juggle three balls over three months; scans showed extra grey matter, the tissue packed with nerve cells, in areas that track moving objects, and it shrank back once they stopped practising. A follow-up in 2008 found the same kind of change in volunteers around 60 years old, although they learned less well than 20-year-olds. The best-known example comes from London, where Katherine Woollett and Eleanor Maguire followed trainee taxi drivers for four years as they memorised the city's 25,000 streets. Those who passed the exam gained grey matter at the back of the hippocampus, a region involved in finding our way; those who failed, and people who never trained, showed no such change.

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StillnessHealth

A 2013 study in mice found that the brain cleared amyloid-beta, a protein that builds up in Alzheimer's disease, faster during sleep. A 2024 mouse study, which used a small fluorescent dye and different methods, found clearance was slower during sleep. Scientists are still debating how sleep affects the brain's waste removal.

The 2013 study came from Maiken Nedergaard's laboratory at the University of Rochester, which in 2012 had described what it called the glymphatic system: cerebrospinal fluid, the clear liquid around the brain, flows in along channels around blood vessels and washes through the tissue. Her team reported that the space between brain cells widened by about 60% during sleep, letting fluid flow more freely. In 2024 Nick Franks and William Wisden at Imperial College London measured the movement of dyes directly and found clearance markedly reduced in sleeping and anaesthetised mice. In 2025 Nedergaard's group reported that during non-REM sleep, the stages without the rapid eye movements of dreaming sleep, which fill most of the night, slow waves of the chemical messenger noradrenaline make blood vessels tighten and relax, pumping fluid into the brain. The methods differ, and none of these studies was in humans.

Sleep scienceRead card

WonderScience

When caterpillars or other insects chew a plant, it can release airborne chemicals, including the ones that give cut grass its smell. Nearby plants that sense them can strengthen their own chemical defences before they are attacked.

The effect was first reported in 1983. Ian Baldwin and Jack Schultz found that young poplar and sugar maple trees sharing air with damaged plants raised their levels of defensive compounds, such as tannins, within about two days, an idea soon nicknamed “talking trees”. It was met with scepticism for years, but many later studies confirmed that such airborne signals exist, although how strongly plants respond varies with species and conditions. In 2023 Masatsugu Toyota's team at Saitama University in Japan filmed the process as it happened. When thale cress, a small plant widely used in laboratories, was exposed to air from injured plants, calcium signals spread through its leaves almost at once; plant cells use such signals to raise the alarm. Two of the cut-grass compounds were enough to trigger them. The chemicals enter through stomata, the tiny pores in leaves.

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WonderScience

In the double-slit experiment, light or particles such as electrons pass through two narrow slits and leave bright and dark bands on a screen, the mark of overlapping waves. If a detector records which slit each particle went through, the bands disappear.

In the early 1800s, Thomas Young shone light through two narrow openings to argue that light is a wave. Where two waves meet crest to crest they reinforce each other, and where a crest meets a trough they cancel out; physicists call this interference. The real surprise came with matter. Claus Jönsson repeated the experiment with electrons in 1961, and in 1974 Italian physicists sent electrons through a similar set-up one at a time. Each landed as a single dot, yet thousands of dots built up the striped pattern. Similar interference has since been seen with molecules of up to 2,000 atoms and, in 2026, with clusters of more than 7,000 sodium atoms. The pattern does not vanish because a person is watching: any physical interaction that records the path, even with no one looking, disturbs the delicate quantum state that produces the interference.

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WonderTechnology

In 1984 and 1985, John Clarke, Michel Devoret and John Martinis showed that a whole electrical circuit on a chip, cooled almost to absolute zero, can behave as a single quantum object, just like an atom. The discovery earned them the 2025 Nobel Prize in Physics.

The experiments were done at the University of California, Berkeley, in Clarke's group; Martinis was his doctoral student and Devoret a postdoctoral researcher. Absolute zero, −273.15 °C, is the lowest temperature possible. At the heart of the circuit was a Josephson junction: two superconductors, metals that carry current with no resistance when very cold, separated by an insulating layer only a few atoms thick. Vast numbers of electrons moved together as if they were one particle. The team saw two signs of quantum behaviour: the circuit escaped from a trapped state by tunnelling, slipping through an energy barrier it could not climb over, and it absorbed microwave energy only in fixed steps, or quanta, as an atom does. Circuits of this kind are now the qubits, the basic units of information, in the superconducting quantum computers built by companies such as Google and IBM.

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WonderScience

The Greenland shark is the longest-living vertebrate known. Radiocarbon dating of one large individual put its age at about 392 years, though the method's own uncertainty range spans roughly 270 to over 500 years.

A Danish-led team reported the result in the journal Science in 2016, after studying 28 Greenland sharks collected in Greenland waters. They radiocarbon-dated the core of each shark's eye lens, which forms before birth and never changes afterwards; radiocarbon dating measures how much of a slowly decaying form of carbon remains. The largest shark, about 5 metres long, came out at 392 years, with a range of roughly 272 to 512 years, so the study cannot say for sure whether it was alive in 1564, when Shakespeare was born. Greenland sharks live in the cold, deep waters of the North Atlantic and Arctic, grow about a centimetre a year or less and may not breed until around 150.

Nielsen et al., Science (2016)Read card

StillnessScience

Light pollution, the glow from artificial light we do not need at night, now hides the Milky Way from about a third of humanity. It also blurs the darkness that birds, insects, plants and people rely on to rest, find their way and tell night from day.

The figure comes from a world atlas of night-sky brightness published in 2016, which found the Milky Way hidden from about 60 per cent of Europeans and nearly 80 per cent of North Americans. Night-migrating birds partly steer by the stars and are drawn towards lit towers and buildings, where many circle until exhausted or fly into glass; US estimates for deaths at towers alone run from four or five million birds a year to ten times that. Insects swarm and die around lamps, and artificial light can shift when some plants come into bud. Programmes such as Toronto's Fatal Light Awareness Program ask building owners to switch off lights during migration.

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WonderSpace

On 30 June 1908 a space rock, probably a stony asteroid 50 to 60 metres wide, exploded in the air above the Tunguska region of Siberia and flattened about 2,000 square kilometres of forest. No impact crater has ever been found.

The asteroid is thought to have burst 5 to 10 kilometres above the ground, so the blast knocked trees down instead of digging a hole. They fell in a vast butterfly-shaped area about 70 kilometres across, all pointing away from the centre, while some trees right below the blast stayed upright, stripped of their branches. Estimates of the energy range from 3 to 50 megatons of TNT, hundreds of times the Hiroshima bomb. The region was so remote, and Russia so shaken by war and revolution, that Leonid Kulik's expedition reached the site only in 1927. Witnesses at a trading post 65 kilometres away felt the heat. It is still the largest impact event in recorded history.

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WonderScience

Deliberately smiling can make people feel slightly happier. In 2022 a study of nearly 4,000 people in 19 countries found that posing a smile, or copying a smiling face, raised reported happiness a little; a subtler method, holding a pen between the teeth, gave less clear results.

The idea that the face can feed back into feelings, called the facial feedback hypothesis, goes back to Charles Darwin and William James. In a famous 1988 experiment, Fritz Strack and colleagues had people hold a pen in their teeth, which forces a smile, or between their lips, which prevents one, and those in the first group rated cartoons as funnier. In 2016, seventeen laboratories repeated that experiment exactly and found no effect. A 2019 review of 138 studies concluded that the effect is real but small and varies from study to study. The 2022 Many Smiles Collaboration, led by Nicholas Coles and designed jointly by supporters and sceptics of the idea, found that deliberate smiling could both strengthen and start feelings of happiness, while the pen method remained inconclusive.

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WonderScience

A 2016 estimate found that a typical adult man weighing 70 kg has about 30 trillion human cells and 38 trillion bacteria. That overturned the old claim that bacteria outnumber our own cells ten to one: the two numbers are roughly equal.

The estimate comes from Ron Sender, Shai Fuchs and Ron Milo of the Weizmann Institute of Science in Israel. Their reference man is 20 to 30 years old, 170 cm tall and weighs 70 kg. The ten-to-one figure, they found, went back to a single rough calculation from 1972 that had been repeated for decades. Almost all the bacteria live in the colon, the last part of the gut, and together they weigh only about 0.2 kg. Among human cells, red blood cells dominate the count, making up about 84 per cent, while fat and muscle cells, far fewer but much larger, make up most of the body's cell mass. The balance also shifts through the day: a single trip to the toilet empties a quarter to a third of the colon's contents.

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WonderScience

An adult body replaces about 330 billion cells every day, around 80 grams of cells, according to a 2021 estimate by scientists at the Weizmann Institute of Science. Close to nine in ten of those cells are blood cells.

Ron Sender and Ron Milo combined the number, mass and lifespan of every major cell type in the body. Short-lived cells dominate the count. Red blood cells live about four months, and neutrophils, the most common white blood cells, only days, so the bone marrow must make vast numbers of them every day. By mass, the largest shares come from blood cells and from the cells lining the gut, which are shed and replaced within days. At this pace, a number of cells equal to all the roughly 30 trillion human cells in the body is replaced in about three months. That does not mean the whole body is renewed: most nerve cells in the brain last a lifetime, and heart muscle cells are replaced only very slowly.

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WonderScience

Your gut and brain communicate through nerves, hormones, immune signals and microbes, which is why stress and digestion can affect each other.

Scientists call this link the gut–brain axis. The gut has its own network of about 500 million nerve cells, the enteric nervous system, sometimes called the “second brain”, which can run digestion largely by itself. It is connected to the brain mainly through the vagus nerve, a long nerve running from the brainstem down to the abdomen, and most of its fibres carry messages upwards, from the gut to the brain. More than 90 per cent of the body's serotonin, a chemical messenger, is found in the gut. Gut bacteria play a part too: in a 2004 Japanese study, mice raised entirely free of germs overreacted to stress. Stress can speed up or slow down the gut, one reason it often worsens irritable bowel syndrome, a common gut disorder. Most research on the microbes' role has been in animals, and human evidence is still limited.

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WonderScience

A placebo is a dummy treatment, such as a sugar pill. In pain studies, placebos can reduce the pain people report and also dampen activity in the brain areas that process pain, even though they contain no active drug.

The word placebo is Latin for “I shall please”. One of the first clues that the effect is physical came in 1978, when Jon Levine and colleagues studied patients recovering from wisdom tooth removal. They gave them a placebo and naloxone, a drug that blocks the effect of endorphins, the body's own painkilling chemicals. In patients who had responded to the placebo, naloxone increased the pain, which suggested that the placebo relief came from endorphins. In 2004 Tor Wager and colleagues used brain scans to show that a placebo painkiller reduced activity in pain-processing regions during a painful stimulus. Expectation works the other way too: in the nocebo effect, from the Latin for “I shall harm”, expecting harm makes symptoms worse. None of this means the pain was imaginary, or that placebos can replace effective treatment.

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WonderScience

Emotions are not only feelings in the head. Fear speeds up the heart and breathing, grief can take away appetite and sleep, and joy changes posture and expression. These bodily changes are part of the emotion itself, and sensing them may be part of how we come to feel it.

In 1884 the American philosopher and psychologist William James turned the usual order around in an essay called “What Is an Emotion?”. We do not tremble because we are afraid, he argued; we feel afraid because we tremble. The physiologist Walter Cannon attacked the idea in 1927, and the debate ran for decades, but modern research keeps finding the body at the heart of emotion. In 2014 Lauri Nummenmaa and colleagues in Finland asked 701 people to colour in body outlines to show where they felt activity rise or fall with different emotions. Most emotions showed up in the chest, where breathing and heartbeat change; anger and happiness also lit up the arms, sadness appeared as weakened arms and legs, and disgust centred on the throat and stomach. The maps were similar for Finnish, Swedish and Taiwanese participants.

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WonderScience

A small patch of specialised cells in the heart, the sinoatrial node, fires an electrical signal on its own that starts every heartbeat. The nerves do not create the beat; they only speed it up or slow it down.

The sinoatrial (SA) node is a strip of tissue about 15 millimetres long in the wall of the right atrium, the heart's upper right chamber. The electrical charge of its cells drifts upwards on its own until it reaches a trigger point and fires, again and again, so no outside command is needed. The signal spreads across both atria, pauses briefly at a second cluster, the atrioventricular node, so the upper chambers can empty, and then races through the lower chambers so they contract together. Arthur Keith and Martin Flack described the node in 1907. At rest the heart beats about 60 to 100 times a minute, with the vagus nerve from the brain holding the node below its own faster pace. If the node fails, other parts of the heart's wiring can take over at a slower rate, or doctors fit an artificial pacemaker.

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WonderScience

After many infections and vaccines, the body keeps memory cells, types of white blood cell that recognise the germ involved. They can last for decades, so if the same germ returns, the immune system responds faster and more strongly.

There are two main kinds of memory cell. Memory B cells can quickly produce antibodies, proteins that latch onto a specific germ, while memory T cells direct the attack or kill infected cells. An early careful record of lasting immunity came from the Danish doctor Peter Panum, who studied a measles epidemic on the Faroe Islands in 1846. Measles had not reached the islands since 1781, and none of the elderly islanders who had caught it then fell ill again. Modern studies agree. In 2003, researchers found memory B cells against smallpox in people vaccinated more than 50 years earlier, and these cells responded strongly to a new dose. In 2008, survivors of the 1918 flu pandemic still had B cells making antibodies against that virus, nearly 90 years later.

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WonderScience

A fever is not the body overheating by accident: signals from the immune system tell the brain to raise its target temperature, rather like turning up a thermostat. The extra heat can help immune cells work and slow down some germs.

Body temperature is controlled by the hypothalamus, a small region at the base of the brain. During an infection, substances called pyrogens trigger the release of a molecule called prostaglandin E2, which raises the hypothalamus's target, or set point. Until the body reaches the new target it feels cold, so you shiver and get the chills; when the fever breaks, you sweat to shed the extra heat. Paracetamol and ibuprofen lower a fever by blocking prostaglandin production. Fever is an ancient defence: even cold-blooded animals such as lizards run one by moving somewhere warmer. In 1975, Matthew Kluger and colleagues infected desert iguanas with bacteria and kept them at different temperatures; the lizards kept warm enough to have a fever survived more often. A very high or long-lasting fever still needs a doctor.

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WonderScience

Sleep is more than rest: during the night the brain strengthens and sorts what it learned during the day and helps keep emotions in balance, while the body releases growth hormone and carries out repairs.

A night's sleep runs in cycles of about 90 minutes. Each cycle moves from light sleep into deep sleep and then into REM sleep, named after the rapid eye movements that come with it and the stage with the most vivid dreams. As early as 1924, the psychologists John Jenkins and Karl Dallenbach found that two volunteers remembered more of the nonsense syllables they had learned if they slept afterwards than if they stayed awake for the same time. In 2007, brain scans showed that after a night without sleep, the amygdala, an area involved in emotional reactions, responded far more strongly to upsetting pictures. In 2013, a study in mice found that the spaces between brain cells widen by about 60 per cent during sleep, helping fluid wash away waste. Regularly sleeping too little harms attention, learning and mood.

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WonderScience

Scientists still have no single accepted explanation for why we dream. Dreams are most vivid in REM (rapid eye movement) sleep but also occur in other stages, and research links them with memory, emotion and the brain's own activity at night.

In 1953, Eugene Aserinsky and Nathaniel Kleitman at the University of Chicago noticed bursts of rapid eye movements (REM) during sleep and linked them to dreaming; people woken during REM sleep report a dream about 80 per cent of the time. Later studies found that people woken from other stages also report dreams, usually shorter and less story-like. Explanations differ. Sigmund Freud, in The Interpretation of Dreams (1899), saw dreams as disguised wishes. In 1977, Allan Hobson and Robert McCarley proposed that dreams are the brain's attempt to make a story out of random signals from the brainstem, the part of the brain that joins the spinal cord. Other researchers argue that dreams help us rehearse threats, sort memories or soften emotional experiences. Each theory explains some dreams, and none explains them all.

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WonderScience

Pain is not a direct reading of damage: the nervous system produces it, weighing signals from the body against danger, attention, memory and context. That is why the same injury can hurt very differently from one person or moment to the next.

Nerve endings called nociceptors detect heat, pressure or chemicals that could harm tissue and send warning signals to the spinal cord and brain, but it is the brain that decides whether, and how much, it hurts. During the Second World War, the American anaesthetist Henry Beecher found that most of the badly wounded soldiers he treated did not ask for morphine, perhaps because surviving and leaving the battle outweighed the injury. In 1965, Ronald Melzack and Patrick Wall proposed the gate control theory: signals can be turned up or down in the spinal cord, which is partly why rubbing a knock helps. Phantom limb pain, felt in an arm or leg that has been amputated, shows that pain can exist where there is no tissue. In 2020 the International Association for the Study of Pain revised its definition, noting that pain and nociceptor activity are not the same thing.

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WonderScience

The first vaccine, made by the English doctor Edward Jenner in 1796, protected against smallpox. In 1980 the World Health Organization declared smallpox eradicated, the first and still the only human disease wiped out worldwide.

Long before Jenner, people in China, India and the Ottoman Empire protected children by variolation, deliberately giving them a mild dose of smallpox. Lady Mary Wortley Montagu, the British ambassador's wife, saw it in Istanbul and had her son inoculated there in 1718. Jenner noticed that milkmaids who caught cowpox, a mild disease of cattle, seemed to be safe from smallpox, and in 1796 he tested this on an eight-year-old boy, James Phipps. The word vaccine comes from vacca, Latin for cow. Even so, smallpox killed an estimated 300 million people in the 20th century. In 1967 the WHO stepped up a global campaign built on surveillance and ring vaccination: finding every case and vaccinating everyone around it. The last natural case was a hospital cook in Somalia, Ali Maow Maalin, in October 1977.

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WonderScience

In 1928, at St Mary's Hospital in London, Alexander Fleming saw that a stray mould had stopped bacteria growing around it on a lab dish, and later named its active substance penicillin. From 1939 an Oxford team led by Howard Florey and Ernst Chain purified it and proved it could cure infections.

Fleming came back from a holiday in September 1928 to find a dish of Staphylococcus bacteria spoiled by a Penicillium mould, with a clear ring around it where the bacteria had died. He published his findings in 1929 but could not make the substance pure or stable enough to use as a drug. In Oxford, Florey, Chain, Norman Heatley and colleagues learned to grow the mould and extract penicillin, and in May 1940 showed that it protected infected mice. In February 1941 they gave it to their first patient, an Oxford policeman; he improved, but the supply ran out and he died. American factories then scaled up production, and 2.3 million doses were ready for the Normandy landings in 1944. Fleming, Florey and Chain shared the 1945 Nobel Prize in Physiology or Medicine. In his Nobel lecture Fleming warned that taking too little penicillin could make bacteria resistant to it.

Alexander Fleming, 1928Read card

WonderScience

On 8 November 1895, in his laboratory at the University of Würzburg in Germany, Wilhelm Röntgen found invisible rays that pass through skin and flesh but are stopped by bone and metal. He called them X-rays, X for unknown, and in 1901 received the first Nobel Prize in Physics.

Röntgen was passing electricity through a glass tube covered in black cardboard when he noticed a coated screen on a nearby bench begin to glow. For weeks afterwards he almost lived in his laboratory, studying the new rays. About six weeks after the discovery he made an X-ray image of his wife Anna Bertha's hand, showing her bones and her ring, and his paper 'On a New Kind of Rays' appeared on 28 December 1895. News spread within days, and doctors were soon using X-rays to look at broken bones. Röntgen refused to patent the discovery so that everyone could benefit from it. Many languages, including German and Turkish, still name the rays after him, which is why an X-ray is a 'röntgen' in Turkish.

Wilhelm Röntgen, 1895Read card

WonderScience

There are more trees on Earth than stars in the Milky Way: about 3 trillion trees, against an estimated 100 to 400 billion stars.

The tree count comes from a 2015 study in the journal Nature, led by the ecologist Thomas Crowther, then at Yale University. His team combined more than 400,000 ground measurements of forest density with satellite images and arrived at about 3.04 trillion trees, roughly 420 for every person alive. Earlier estimates, based on satellite images alone, had put the figure near 400 billion. The study also measured losses: about 15 billion trees are cut down each year, and the number of trees on Earth has fallen by around 46 per cent since the start of human civilisation.

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WonderScience

Horseshoe crab blood clots at the faintest trace of toxins from bacteria. Since the 1970s an extract of it, called LAL, has been used to check that injectable medicines and implants are free of them.

Horseshoe crabs are not true crabs; they are closer relatives of spiders and scorpions. Their blood is blue because it carries oxygen with haemocyanin, a copper-based molecule. In 1956 the American scientist Frederik Bang found that bacteria make the blood gel. The toxins behind this, endotoxins, are fragments of the outer wall of certain bacteria and can cause dangerous fevers in the bloodstream. LAL stands for Limulus amebocyte lysate, an extract of the crab's blood cells; the United States approved it in 1977. Collecting it means bleeding wild crabs, and studies suggest up to about 30 per cent may die afterwards. A synthetic alternative, recombinant factor C, has been sold since 2003 and was accepted in the official rulebooks for medicine testing, the European Pharmacopoeia in 2016 and the US Pharmacopeia in 2025.

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WonderScience

Pando, a grove of about 47,000 aspen trunks in Utah, is a single organism: every trunk grows from one shared root system and carries the same genes.

Pando, Latin for 'I spread', is a clone of quaking aspen covering about 43 hectares of Fishlake National Forest in Utah. Aspens can reproduce by sending up new shoots from their roots, so what looks like a forest is one plant with many stems. Foresters Jerry Kemperman and Burton Barnes identified it as a single organism in 1976, and the ecologist Michael Grant later gave it its name. Weighing an estimated 6,000 tonnes, it is among the heaviest living things known. Its age is uncertain: charcoal studies from 2022 point to at least 9,000 years, and a 2024 genetic study suggested 16,000 years or more. Today Pando is thinning, because deer, elk and cattle eat its young shoots.

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WonderScience

Wombats, burrowing marsupials from Australia, are the only animals known to produce cube-shaped droppings.

A team led by Patricia Yang and David Hu at the Georgia Institute of Technology studied wombats that had died in road accidents in Tasmania. They found that the last part of the intestine has stiffer and more elastic bands side by side, and as the droppings slowly dry and move along, those uneven walls press them into cubes with fairly sharp corners. A wombat can leave 80 to 100 cubes a night, often on rocks and logs where it marks its territory, and the flat sides may help stop them rolling away. The work won the 2019 Ig Nobel Prize in physics, a light-hearted award for research that makes people laugh, then think.

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WonderScience

Flamingos are not born pink. Their chicks hatch grey, and the adults' pink comes from pigments in the algae and tiny shrimp they eat.

The pigments are carotenoids, the same family that colours carrots and tomatoes. Flamingos filter tiny algae, brine shrimp and other small creatures from shallow, salty water, and enzymes in the liver turn the carotenoids into the pinks and reds laid down in growing feathers. Chicks take a few years to reach full adult colour. The amount of pigment in the diet shows: American flamingos of the Caribbean are the reddest, while the lesser flamingo is much paler. Parents feed their chick a pigment-rich 'crop milk' made in the throat, and often fade while doing so. In zoos, flamingos are given carotenoid supplements; without them they gradually turn pale.

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WonderScience

Some freshwater turtles can take in oxygen through the cloaca, the opening under the tail, which helps them stay underwater for long periods.

The cloaca is the single opening that amphibians, reptiles and birds use both to pass waste and to reproduce. In some turtles it leads to thin-walled pouches packed with blood vessels, where oxygen dissolved in the water passes into the blood; biologists call this cloacal respiration. Australia's Fitzroy River turtle relies on it so heavily that it can stay underwater for long stretches, pumping water in and out of these pouches. In North America, painted turtles and some other species spend the winter under the ice of frozen ponds, where they cannot reach the surface at all. Their bodies slow right down, and they take in small amounts of oxygen through the skin and the cloaca.

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WonderScience

Iceland was long one of the very few inhabited places with no mosquitoes; the first ones were found there in October 2025.

Biologists' main explanation for Iceland's long mosquito-free record is its changeable winters: repeated cycles of freezing, thawing and freezing again can kill larvae before they grow into flying adults. On 16 October 2025, at Kiðafell in the Kjós district north of Reykjavík, a local insect enthusiast caught several mosquitoes, which experts identified as Culiseta annulata, a large, cold-hardy species common across Europe. Both males and females were among them, and they were the first confirmed in the country. No more were found during the summer of 2026, so for now this looks like a one-off arrival rather than a settled population, although warmer winters could make one more likely in future.

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WonderScience

A hummingbird can fly backwards, and its heart can beat over 1,000 times a minute.

Hummingbirds, found only in the Americas, are the only birds that can hover for long periods and fly backwards. Their wings trace a figure of eight in the air, and small species beat them up to about 80 times a second. All this takes enormous energy: in flight a hummingbird's heart can beat more than 1,000 times a minute, among the fastest heartbeats of any animal. To get through the night without running out of fuel, many species enter torpor, a deep, cold state like a short hibernation. Heart rate and body temperature fall sharply, sometimes close to the temperature of the surrounding air, and the bird uses far less energy until morning.

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WonderScience

Mangroves, trees that grow in salt water on tropical coasts, protect shorelines by slowing waves and store large amounts of carbon in the mud beneath them.

Mangrove roots, some sticking up out of the mud like snorkels to take in air, slow waves, trap sediment and limit erosion, and their tangle of underwater roots shelters fish, crabs and young sea creatures. Mangrove forests also hold large amounts of 'blue carbon', the name for carbon stored by coastal and ocean ecosystems. Much of it lies in the waterlogged, oxygen-poor mud, where dead plant matter rots so slowly that carbon can stay buried for centuries. Studies of tropical forests have found that, area for area, mangroves are among the most carbon-rich forests on Earth. Clearing them for shrimp farms or building therefore releases carbon as well as destroying habitat and natural coastal defences.

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WonderScience

Peatlands cover only about 3 percent of the world's land, yet hold roughly twice as much carbon as all its forests. They form as partly rotted plants pile up in waterlogged ground over thousands of years.

Peat is the dark, spongy material that builds up where waterlogged, oxygen-poor ground slows the decay of dead plants almost to a stop; mosses, especially sphagnum, are often its main source. It grows very slowly, around a millimetre a year, so a few metres of peat can hold thousands of years of history. Peatlands range from the bogs of Ireland and Scotland to vast areas of Siberia and Canada, and to tropical peat swamps in Indonesia and the Congo Basin. When they are drained for farming or forestry, or catch fire, carbon that took millennia to build up can escape within years. That is why rewetting drained peatlands is now part of many countries' climate plans.

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WonderScience

The Svalbard Global Seed Vault, dug into a mountain on a Norwegian Arctic island, stores duplicate seed samples from genebanks around the world. The original collections stay in use elsewhere; Svalbard is the safety copy.

A genebank keeps seeds of crop varieties and their wild relatives so that breeders and researchers can use them. The Svalbard vault opened on 26 February 2008 and is run jointly by the Norwegian government, the Crop Trust and the Nordic Genetic Resource Center (NordGen). The seeds are kept at about -18°C, and depositors keep ownership under a 'black box' system: only the institution that deposited a box can open or withdraw it. The backup has been needed. When the war in Syria cut off the main genebank of the international research centre ICARDA near Aleppo, ICARDA withdrew samples from Svalbard in 2015, and again in 2017, to rebuild its collection in Lebanon and Morocco. These remain the only withdrawals.

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WonderScience

Lake Baikal in Siberia, 25 to 30 million years old and 1,642 metres deep, is the world's oldest and deepest lake.

Baikal lies in a rift, a place where the Earth's crust is slowly pulling apart; the gap still widens by about 4 millimetres a year. The lake holds more than a fifth of all the fresh water in the world's lakes and rivers, more than North America's five Great Lakes put together. Millions of years of isolation have produced plants and animals found nowhere else, including the Baikal seal, the only seal species that lives entirely in fresh water, and more than 350 kinds of small, shrimp-like creatures called amphipods. In winter the surface freezes so thick that marked roads run across the ice.

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WonderScience

Some Great Basin bristlecone pines in the western United States are more than 4,800 years old, older than Egypt's Great Pyramid of Giza.

The oldest known living one, nicknamed Methuselah, grows in the White Mountains of eastern California; counting its growth rings shows it is more than 4,850 years old, and its exact location is kept secret to protect it. The Great Pyramid was built around 2560 BCE, a few centuries after Methuselah sprouted. Bristlecones grow extremely slowly on thin, dry dolomite soil, a rock similar to limestone, where few other plants survive, which spares them competition and fire. Their dense, resin-filled wood resists insects, fungi and rot, and dead trees can stand for thousands of years. In 1964 a researcher in Nevada cut down one tree, later called Prometheus, and counted at least 4,862 rings, making it the oldest tree then known.

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