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Not a fact anymore
Many acids contain oxygen, but some do not. Hydrochloric acid, hydrobromic acid, and hydroiodic acid are familiar counterexamples.
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For most uncomplicated acute low-back pain, prolonged bed rest provides no advantage and can delay recovery. Patients are generally encouraged to remain active as tolerated while serious causes are assessed when warning signs are present.
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Adult human heart-muscle cells, called cardiomyocytes, do renew, but very slowly. Estimates suggest that roughly 1% are replaced each year in younger adults, with the rate falling with age. That is far too little to rebuild the large amount of muscle lost in a major heart attack.
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The adult human mandible is a single bone. It develops from two embryonic halves that normally fuse at the mandibular symphysis during the first year of life.
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Adult brains can produce new neurons, a process called neurogenesis, in limited regions in many animals. How much new-neuron formation continues in adult humans—especially later in life—remains actively debated.
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Gases are matter with mass. Air has weight, exerts pressure, and can be compressed, transferred, and weighed.
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Air is a mixture of gases, mainly nitrogen and oxygen, with smaller amounts of argon, carbon dioxide, water vapor, and other gases.
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The Amazon is not a single, uniform carbon sink. Aircraft measurements showed southeastern Amazonia becoming a net carbon source during the 2010s, while the carbon balance of the basin as a whole remains uncertain and varies by method.
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Many classical sculptures were painted, gilded, inlaid, or otherwise colored. Some received full polychromy, while others used selective color to emphasize skin, hair, clothing, eyes, or attributes.
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Antarctica has experienced much warmer climates. At different times it supported forests, dinosaurs, and later marsupial mammals, even at high southern latitudes.
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Arteries carry blood away from the heart. Systemic arteries normally carry oxygenated blood, while pulmonary arteries carry deoxygenated blood to the lungs.
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Inhaled asbestos fibers cause mesothelioma and increase the risks of lung, laryngeal, and ovarian cancers. They also cause asbestosis and other pleural disease.
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Most asteroid-belt material is leftover planet-building material that never assembled into a full planet, largely because Jupiter's gravity disrupted accretion.
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Asthma is a chronic inflammatory airway disease involving variable airflow obstruction and airway hyperresponsiveness. Stress and emotion can influence symptoms, but they are not the underlying cause of asthma.
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Chemical equilibrium is dynamic. Forward and reverse processes continue at equal rates, leaving concentrations and other macroscopic properties approximately constant.
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Temperature does not keep falling all the way up through the atmosphere. It usually decreases through the troposphere, the lowest layer where most weather occurs, but begins rising through much of the stratosphere because ozone absorbs ultraviolet sunlight and converts some of that energy to heat.
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Ordinary atomic nuclei are composed of protons and neutrons. Electrons occupy quantum states outside the nucleus, although beta decay can create and emit electrons during a nuclear transformation.
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Atoms contain electrons and a nucleus made of protons and usually neutrons. Protons and neutrons are themselves made of quarks, while electrons are currently treated as elementary particles.
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An element can contain several isotopes. Its isotopes have the same number of protons but different numbers of neutrons, giving them different masses.
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Autism is a neurodevelopmental condition shaped strongly by genetics and early development. Parenting style does not cause it.
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Healthy infants should normally be placed on their backs for sleep. Prone sleeping substantially increases the risk of sudden infant death syndrome.
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Bacteria have organized interiors. They use structural proteins to control cell shape, position internal components, and organize cell division. Some of these proteins are relatives of actin and tubulin, major parts of the cytoskeleton in animal and plant cells.
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Bacterial and human cell numbers are roughly comparable. One widely cited estimate for a reference adult male is about 38 trillion bacterial cells and 30 trillion human cells, a ratio near 1.3 to 1.
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Barnacles are crustaceans related to crabs, lobsters, and shrimp. Their free-swimming larvae and jointed appendages reveal that relationship.
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Copper, iron, lead, silver, gold, and other metals are distinct chemical elements defined by atomic number. Ordinary chemical reactions cannot turn one element into another; elemental transmutation requires nuclear processes.
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Many parts of Amazonia were substantially shaped by Indigenous societies before European contact. Archaeologists have found settlements, roads, canals, raised fields, large earthworks, engineered soils, and long-term forest management. The scale of occupation varied greatly across the enormous basin.
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Beriberi is caused by thiamine deficiency. It can damage the nervous system, the cardiovascular system, or both.
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Selected beta blockers are standard treatment for stable heart failure with reduced ejection fraction, meaning the heart pumps out a smaller-than-normal share of the blood in its main chamber with each beat. When introduced carefully, these drugs reduce hospitalization and improve survival.
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The central Arctic is an ocean historically covered by extensive sea ice, although the ice is seasonal and rapidly declining under modern climate warming. Polynyas and local open water do not imply a permanently open polar sea.
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Birds vary widely in olfactory ability. Many use smell to navigate, find food, recognize individuals and nests, detect predators, and choose mates.
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Black holes are real astrophysical objects. Evidence comes from stellar and gas motions, accretion radiation, gravitational waves, and horizon-scale imaging, and black holes occur across a wide range of masses.
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The heart pumps blood through a closed circulatory system. Blood repeatedly travels through arteries, capillaries, and veins, carrying gases, nutrients, hormones, wastes, and immune cells.
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Blue-green algae are cyanobacteria: bacteria that perform photosynthesis. Unlike true algae, their cells have no membrane-bound nucleus or chloroplasts.
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Evolution mainly works through inherited variation: genetic differences that can be passed from parents to offspring. Changes acquired during an individual's life—such as stronger muscles from exercise or the loss of a limb—are not generally written back into the inherited genetic material. Some environmental effects can persist across generations, but they are much narrower than classical Lamarckian inheritance.
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Adipose tissue is metabolically active and functions as an endocrine and immune organ. It secretes hormones and signaling molecules that influence appetite, insulin sensitivity, inflammation, reproduction, and vascular biology.
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Bone is not only structural tissue. It is constantly rebuilt, stores and releases minerals, produces blood cells in its marrow, and also sends chemical signals to distant organs. One well-established example is FGF23, a hormone made mainly by bone cells that helps the kidneys control phosphate and vitamin D.
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Milk is synthesized by mammary epithelial cells from nutrients and water supplied through the bloodstream, under hormonal regulation involving prolactin, oxytocin, estrogen, progesterone, and other signals. It is not transformed menstrual blood.
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Many adults retain metabolically active brown adipose tissue, especially around the neck and upper chest. Its amount and activity vary with age, temperature, body composition, and other factors.
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Combustion is a set of chemical oxidation reactions. In ordinary burning, a fuel reacts with oxygen and forms new products while releasing energy.
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California is part of mainland North America. Baja California is a peninsula bounded by the Pacific Ocean and the Gulf of California, while the modern U.S. state of California is continuous with the continent.
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Carbon can form many allotropes—different structures made entirely from the same element. Diamond and graphite are two examples, but carbon also forms fullerenes, carbon nanotubes, graphene, and other structures with very different shapes and properties.
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Appendectomy remains a standard and highly effective treatment, but selected patients with imaging-confirmed uncomplicated appendicitis can be managed initially with antibiotics, accepting a meaningful risk of recurrence or later surgery.
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A cataract is an opacity of the eye's natural crystalline lens itself.
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A person's cells begin from one fertilized egg but accumulate mutations as they divide. The result is somatic mosaicism: genetically distinct cell lineages within the same body.
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Cell membranes are flexible double layers of lipid molecules with proteins embedded in or attached to them. The lipids and many proteins can move sideways within the membrane, and cells organize them into changing clusters and specialized regions.
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Functional lymphatic vessels exist in the meninges, the protective membranes surrounding the brain. They help drain fluid and immune material toward lymph nodes in the neck. This is different from having a dense lymphatic network running through the brain tissue itself.
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Nearly all cervical cancers are caused by persistent infection with high-risk types of human papillomavirus, or HPV. HPV is very common and most infections clear on their own, but some high-risk infections persist and can gradually disrupt the controls that keep cervical cells from growing abnormally.
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Changes in gravity do not act everywhere at once. In general relativity, gravity is part of the structure of spacetime, and changes in the gravitational field propagate at the speed of light. Rapidly accelerating masses can produce traveling disturbances called gravitational waves.
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Elements can transform through radioactive decay and nuclear reactions. Changing the number of protons in a nucleus changes one element into another.
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CFCs—chlorofluorocarbons once widely used in refrigerants and aerosol propellants—are so stable near the ground that they can survive long enough to reach the stratosphere. There, ultraviolet sunlight breaks them apart and releases chlorine, which can destroy many ozone molecules in repeated chemical reactions.
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The earliest unambiguous domestic chickens currently come from central Thailand, dating to about 1650–1250 BCE. The archaeological record no longer supports the Indian subcontinent as the first center of domestication.
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Imitation, feedback, and reinforcement contribute to language learning, but they do not explain it alone. Children detect patterns, infer rules, generalize beyond what they hear, and develop language through interacting cognitive, social, and biological processes.
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Cholera is an intestinal infection caused by toxigenic strains of the bacterium Vibrio cholerae, usually acquired through contaminated food or water.
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Genes occupy loci on chromosomes. Chromosome segregation and recombination explain Mendelian inheritance, linkage, sex-linked traits, and genetic mapping.
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Cigarette smoking is the leading cause of lung cancer. Risk rises with cumulative exposure, falls after quitting, and is supported by converging epidemiological, pathological, toxicological, and molecular evidence.
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Classic Maya societies were politically diverse states whose rulers fought wars, took captives, formed alliances, destroyed rival centers, and used violence in dynastic and territorial competition.
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People were present in the Americas before the Clovis culture. Most specialists accept at least some pre-Clovis occupation, although the timing, routes, and number of migrations are still debated.
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Living coelacanths survive today in two known species, Latimeria chalumnae and Latimeria menadoensis.
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Comets contain ice and dust, but their nuclei can be dark, porous, layered, structurally complex, and rich in organics and minerals. Some are better described as icy dirtballs than dirty snowballs.
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Comets are small solar-system bodies, largely composed of ice, dust, and rock, that orbit the Sun. Their visible comae and tails develop when they approach the Sun.
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A brief period of relative rest is usually followed by a gradual return to ordinary activity below the level that substantially worsens symptoms. Prolonged strict rest can delay recovery.
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Only a thin outer layer of a coral colony is living tissue. Reef frameworks contain accumulated calcium-carbonate skeletons, dead coral, sediments, algae, sponges, microbes, and many other organisms.
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Corals are animals in the phylum Cnidaria. Each colony is made of polyps that capture food, digest it, and often live in partnership with photosynthetic algae.
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Most cosmic rays are high-energy atomic nuclei and other charged particles. They produce secondary particle showers when they strike Earth's atmosphere.
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A crystal can be highly ordered without repeating the same atomic pattern over and over. Quasicrystals have this nonrepeating order, yet they still produce the sharp diffraction patterns characteristic of crystals.
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The lens refracts and focuses incoming light, but the retina is the light-sensitive neural tissue that detects photons and begins visual processing.
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Many nonhuman animals acquire behaviors socially and maintain group-specific traditions. Documented examples include tool use, songs, migration routes, foraging methods, and local conventions.
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DDT is persistent and fat-soluble, so it can build up inside organisms and become more concentrated higher in a food chain. One of its breakdown products, DDE, can thin eggshells in sensitive birds and reduce reproductive success.
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Animals and microorganisms inhabit the ocean at depths far beyond 300 fathoms (549m, 1800ft) including the deepest trenches. Deep-sea ecosystems can be supported by sinking organic matter, chemosynthesis and other energy pathways.
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The seafloor contains enormous mountain ranges, deep trenches, volcanic ridges, seamounts, fracture zones, canyons, and broad abyssal plains.
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DES does not prevent miscarriage. Prenatal exposure can cause rare clear-cell cancers and reproductive abnormalities in exposed daughters and other health effects in exposed children.
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Non-avian dinosaurs became extinct about 66 million years ago, but one dinosaur lineage survived: birds. In modern phylogenetic classification, birds are living avian dinosaurs.
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Dire wolves were not close gray-wolf relatives within Canis. Ancient DNA first showed a much deeper split in 2021, and higher-coverage genomes published in 2026 now suggest that dire wolves had an admixed ancestry involving two ancient canid lineages.
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Dreaming can occur during both REM and non-REM sleep. REM dreams are often more vivid and story-like, but non-REM awakenings can also produce detailed dream reports.
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One gene can produce several RNA or protein products through alternative splicing, different promoters, and other forms of RNA processing. Some genes produce functional RNA rather than protein.
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The earliest known hominins and the first several million years of human evolutionary history are African. Homo later dispersed repeatedly into Eurasia, where additional human lineages evolved.
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Rapid juvenile growth was already present in some stem tetrapods more than 320 million years ago. Early tetrapods used a wider range of growth strategies than the old amphibian-like ancestral model allowed.
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Earth is an oblate spheroid: nearly spherical, slightly flattened at the poles, and held together by gravity rather than supported by air beneath a flat surface.
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Earth formed about 4.54 billion years ago. Radiometric dating of meteorites, lunar material, and Earth's oldest minerals and rocks all support this age.
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Earth rotates once each day and orbits the Sun once each year. The other planets also orbit the Sun, while the solar system itself orbits within the Milky Way.
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Earth’s rigid outer layer is divided into tectonic plates that move relative to one another. Continents form parts of these plates and are carried along as the plates move.
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Earth's core has two main layers: a liquid outer core surrounding a solid inner core. Earthquake waves reveal the difference because different kinds of seismic waves travel differently through solids and liquids.
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Earth's magnetic field has reversed polarity many times. Rocks preserve intervals when magnetic north and south were opposite their present orientation.
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Earth's main magnetic field is generated by a geodynamo in the liquid outer core. Hot, electrically conducting metal moves through the core, creating electric currents that continually sustain the magnetic field. The core is far too hot to behave like an ordinary permanent bar magnet.
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Seismic stations can locate earthquakes from far away by comparing the arrival times and directions of different wave types across a network.
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Most damaging earthquakes result from sudden slip on tectonic faults as accumulated stress overcomes friction. Volcanic processes can generate earthquakes, but they are only one specialized source.
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Succession can follow multiple pathways and may produce different long-lasting states. Disturbance, climate, species arrival, historical contingency, feedbacks, and human activity can prevent or redirect any single endpoint.
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Electric and magnetic fields are coupled aspects of one electromagnetic interaction. Changing electric fields generate magnetic fields, changing magnetic fields generate electric fields, and light is an electromagnetic wave.
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Electrons display both particle-like detections and wave-like interference and diffraction. Quantum mechanics describes them with quantum states rather than as classical particles or classical waves.
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Electrons in atoms do not travel around the nucleus on fixed circular tracks. Quantum mechanics describes them with orbitals: states that tell us the probabilities of finding an electron in different regions and the energies it can have.
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Embryonic form emerges progressively through cell division, differentiation, signaling, gene regulation, morphogenesis, and interactions among tissues. The organism is not present as a complete miniature individual inside the egg or sperm.
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Embryos reflect shared ancestry, but they do not pass through a sequence of complete adult forms of their evolutionary ancestors. Related species often reuse similar developmental structures and genetic programs, then modify them in different ways.
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Humans live throughout the tropics and near the equator. Equatorial regions are generally warm, but habitability depends on rainfall, altitude, ecology, infrastructure, adaptation, and many other factors. There is no lethal solar heat barrier around the equator.
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Equilibrium climate sensitivity estimates how much the planet would eventually warm after atmospheric CO₂ doubled and the climate had time to adjust. IPCC AR6 assessed the likely range as 2.5°C to 4.0°C, with a best estimate of 3°C.
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Some European MRSA lineages carrying the resistance gene mecC arose long before antibiotics were used in medicine. Hedgehogs carry these bacteria alongside a skin fungus that naturally produces β-lactam antibiotics, creating an environment that can favor resistant bacteria without human antibiotic use.
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Observations of distant Type Ia supernovae show that the expansion of the universe is accelerating. The cause is described as dark energy, although its physical nature remains unknown.
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Aggressive venting generally does not purge anger and can maintain or increase arousal, rumination, and aggressive behavior. Strategies that reduce arousal or interrupt rumination are more consistently effective.
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For many early breast cancers, breast-conserving surgery followed by radiation provides survival comparable to mastectomy. Removing additional muscle and tissue does not automatically improve cancer control.
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A large asteroid struck at Chicxulub about 66 million years ago and triggered severe global environmental disruption. This impact was the primary cause of the end-Cretaceous mass extinction.
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Fermentation is carried out by enzymes and metabolic pathways that can continue outside intact cells when the necessary cellular components and conditions are preserved.
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Fibonacci phyllotaxis was not universal among the earliest leafy plants. A 407-million-year-old lycophyte had only non-Fibonacci spirals in the reconstructed shoots, supporting later and probably independent evolution of Fibonacci-dominated patterns in major plant lineages.
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Stars move through the Milky Way. Their slow change in position across the sky is called proper motion and can be measured by astrometry. Constellations therefore change gradually over long timescales.
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The source called Fomalhaut b is best explained as an expanding dust cloud produced by a collision between large planetesimals, not as a planet. Hubble watched the source fade, spread out, and move in a way consistent with dispersing collision debris.
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Some ecosystems do not begin with sunlight. Certain microorganisms can make organic matter using energy released by chemical reactions rather than photosynthesis. This process, called chemosynthesis, can support entire food webs in dark environments such as deep-sea hydrothermal vents.
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Fungi form their own major branch of life. Unlike plants, they do not use photosynthesis to make food; they release digestive enzymes into their surroundings and absorb the resulting nutrients. Molecular evidence also shows that fungi are evolutionarily closer to animals than to plants.
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Galaxies form a cosmic web of clusters, filaments, sheets, and vast voids shaped by gravity acting on early density variations.
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Most gamma-ray bursts are enormous explosions in distant galaxies, not ordinary events inside the Milky Way. Long bursts are linked to the collapse of massive stars, while many short bursts come from mergers of compact objects such as neutron stars.
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Many genes in animals, plants, fungi, and other organisms with cell nuclei are not one uninterrupted stretch of usable information. The first RNA copy contains sections that will be kept, called exons, and sections that will be removed, called introns.
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DNA is the hereditary material in cellular organisms and many viruses. Its nucleotide sequence stores genetic information, while proteins perform many of the functions encoded by that information.
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Most genes remain at stable chromosome locations, but some DNA sequences can move. These transposable elements can cut or copy themselves into new positions, where they can disrupt genes, change gene activity, or contribute to genome evolution.
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Genes usually pass vertically from parents to offspring, but DNA can also move horizontally between unrelated organisms. This is especially common in microbes and can spread useful traits, including antibiotic resistance, without reproduction.
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Cells can copy RNA back into DNA. An enzyme called reverse transcriptase performs this reaction. Retroviruses use it to make a DNA copy of their RNA genome, which can then be inserted into the DNA of an infected cell.
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The Ries and Steinheim craters most likely formed in two separate impacts roughly 0.5–1 million years apart, despite being only about 40 kilometres apart.
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Giant pandas belong to the bear family, Ursidae. Red pandas belong to their own family, Ailuridae, and are more closely related to musteloids such as raccoons, weasels, and skunks.
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Sauropods were primarily terrestrial animals with limbs, feet and skeletons adapted to bearing enormous loads on land. They could enter water and probably could swim, but deep-water immersion was not required to support their bodies; their air-filled skeletal and respiratory system actually made them unusually buoyant and potentially unstable when floating.
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Glial cells do much more than hold neurons in place. Different kinds of glia insulate nerve fibers, control the chemical environment around neurons, supply metabolic support, help shape synapses, regulate local blood flow, guide development, and perform immune functions in the nervous system.
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Sea level has repeatedly risen and fallen by tens to more than 100 meters as ice volume, ocean temperature, seafloor shape, and tectonics changed.
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The stars, glowing gas, planets, and other ordinary matter we can observe directly make up only a small part of the modern cosmic inventory. Gravity requires much more dark matter around galaxies and clusters, while cosmological measurements indicate that dark energy contributes an even larger share of the universe's total energy density.
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Fishing can reduce marine populations below productive levels, collapse individual stocks, alter food webs, and cause long-lasting depletion. Whether a stock recovers depends on biology, habitat, environmental conditions, and management.
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Healthy lungs are not completely sterile. The lower airways contain small numbers of microbes, forming a low-density microbiome shaped by inhaled organisms, tiny amounts of material entering from the mouth and throat, immune clearance, and local conditions.
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Heat is energy transferred because of a temperature difference. Temperature is related to the microscopic motion and internal energy of matter, not to the amount of a conserved heat-fluid stored inside it.
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The Sun, stars, planets, moons, asteroids, and comets are made from the same chemical elements and governed by the same fundamental physics studied on Earth, although their compositions and physical states differ.
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Celestial objects form, evolve, erupt, collide, and die. Stars change over time, the Sun has active surface phenomena, comets move through planetary space, and transient events occur throughout the universe.
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When air resistance is negligible, objects near the same location fall with essentially the same acceleration regardless of their mass.
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Isolated systolic hypertension is a major, treatable risk factor for stroke, heart disease, kidney disease, and death. Treatment targets must still account for frailty, adverse effects, and individual circumstances.
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Most specialists recognize Homo floresiensis as a distinct archaic human species rather than a diseased modern human. Its unusual anatomy appears in more than one individual and includes a combination of primitive traits that a single disorder does not explain well.
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Fossils attributed to early Homo sapiens extend to roughly 300,000 years ago, and many researchers favor a geographically broad African emergence rather than one sudden origin in a single East African population.
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The appendix contains abundant immune tissue and may help maintain or restore gut microbial communities. It is not essential, and most people can live normally after it is removed.
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Vertebrate brains evolved through modification and reorganization of shared structures and interconnected networks. Reptiles possess homologues of structures called limbic or cortical in mammals, and cognition, emotion, and basic regulation are not confined to independent evolutionary layers.
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Human evolution is a branching family tree, not a single ladder. Several hominin species often lived at the same time, many lineages died out without becoming our direct ancestors, and some later branches also interbred.
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Humans have roughly 20,000 protein-coding genes, not about 100,000. A protein-coding gene is a stretch of DNA whose information can be used to make a protein. The exact count continues to change slightly as genome annotation improves.
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Habitual bipedalism, regular walking on two legs, appeared millions of years before the major expansion of brain size seen in the genus Homo. Early hominins retained brains broadly comparable in size to those of living apes.
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Standard anatomical description recognizes four named anatomical lobes of the human liver: right, left, caudate, and quadrate. Modern surgical anatomy also divides the liver functionally into vascular segments.
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Memory is reconstructive. Recall combines stored details with expectations, later information, context, and inference, which can produce confident errors.
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The human uterus has a single main uterine cavity. Fetal sex is determined genetically at fertilization and is not determined by implantation in a particular side or chamber of the uterus.
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A true carotid rete mirabile is present in some animal species but is not a normal structure of human anatomy.
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Ice sheets flow under their own weight. Ice moves from the interior toward fast-flowing outlet glaciers and ice streams, while snowfall, melting, fracture, and ocean interaction continually change the system.
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Identical twins begin with nearly the same inherited DNA because they develop from the same fertilized egg. After the embryo splits, however, new DNA mutations can arise independently in either twin, so their genomes become slightly different over time.
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Diseases have many distinct causes and mechanisms, including infections, genetic changes, immune dysfunction, nutritional deficiencies, environmental exposures, degeneration, and injury. The four humors are not anatomical substances whose balance governs health.
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Cognitive functions emerge from distributed and interacting neural networks in brain tissue. The cerebral ventricles are fluid-filled spaces that contain and circulate cerebrospinal fluid, not chambers housing mental faculties.
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Antibodies are immune proteins that recognize specific targets. Those targets are often foreign, such as parts of microbes or their toxins, but antibodies and immune cells can also recognize the body’s own tissues. Normally the immune system restrains these reactions; when that control fails, autoimmune disease can result.
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Feeding contributes to caregiving, but attachment is a broader need for safety, proximity, comfort, and responsive social contact.
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The kilogram is no longer defined by one physical object. Instead, the SI fixes an exact value for the Planck constant, and laboratories realize the kilogram through precision measurements tied to that value.
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A 2024 taxonomic revision recognizes four king cobra species: Ophiophagus hannah, O. bungarus, O. kaalinga and O. salvatana.
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Most dinosaurs held their tails off the ground as counterbalances, with their spines and bodies in more horizontal, dynamic postures. Routine tail-drag traces are rare in trackways.
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Large carbon-rich molecules occur throughout interstellar and circumstellar space. Astronomers have detected polycyclic aromatic hydrocarbons, carbon chains, fullerenes, and many other organic compounds.
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The weak interaction—the force involved in radioactive beta decay—does not always treat a process and its mirror image the same way. In weak decays, nature can distinguish left from right. Electromagnetic and strong interactions still preserve this mirror symmetry.
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For children, no safe blood-lead level has been identified. Even relatively low exposure is associated with effects on learning, attention, behavior, and brain development. A child can therefore be harmed without showing the dramatic symptoms of acute lead poisoning.
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Legumes such as peas, beans, and clover usually obtain usable nitrogen through a partnership with bacteria called rhizobia. The bacteria live in specialized root nodules and convert nitrogen gas from the air into chemical forms the plant can use; the plant supplies them with energy and shelter.
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A lichen is a stable symbiotic system built mainly from a fungus and one or more photosynthetic partners, often algae or cyanobacteria, along with additional microorganisms.
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Light displays both wave-like and particle-like behavior. Electromagnetic radiation is quantized into photons while also producing interference, diffraction, and other wave phenomena.
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Light travels more slowly through ordinary transparent materials such as water and glass than through vacuum or air. Their refractive index is related to that reduced propagation speed.
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Light propagates through vacuum at a finite speed of exactly 299,792,458 metres per second. This speed is a fundamental constant and the maximum speed for causal influence in relativity.
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Light can travel through a vacuum without a material carrier. Its behavior is described by electromagnetism, quantum theory, and relativity.
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Platypuses and echidnas are mammals that lay eggs. They have hair, produce milk, and share mammalian ancestry while retaining an ancestral egg-laying reproductive system.
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Microorganisms observed in decaying or fermenting material come from pre-existing organisms or their spores. Ordinary biological reproduction follows biogenesis.
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Many organisms live without molecular oxygen. Anaerobes use fermentation or alternative electron acceptors, and obligate anaerobes can be damaged or killed by oxygen.
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The five-kingdom system—animals, plants, fungi, protists, and monerans—does not accurately represent all major evolutionary relationships. DNA and RNA comparisons showed that organisms once grouped together as Monera actually include two very different lineages, Bacteria and Archaea, while 'Protista' contains many distantly related branches.
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Quaoar, a small body orbiting beyond Neptune, has a dense ring far outside its classical Roche limit, the region where tidal forces can prevent loose ring material from assembling into a moon. The Roche limit is therefore not an absolute outer boundary for dense rings.
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The lungs' central physiological role is gas exchange: bringing oxygen into the blood and removing carbon dioxide. They also contribute to acid-base regulation, filtering, metabolism, and other functions, but they do not exist primarily to cool an innately hot heart.
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Tropical soils vary enormously. Many rainforests grow on old, deeply weathered soils that are poor in readily available nutrients, with productivity sustained by rapid recycling through biomass, litter, roots, fungi, and microbes. Volcanic, alluvial, and younger tropical soils can be naturally fertile.
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Rocks form in several fundamentally different ways. Igneous rocks such as basalt and granite crystallize from molten rock; sedimentary rocks form from deposited material or substances precipitated from water; and metamorphic rocks form when older rocks are transformed by heat, pressure, or fluids.
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Malaria is caused by Plasmodium parasites and is usually spread through the bites of infected female Anopheles mosquitoes.
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Fossil synapsid vertebrae do not support a simple shift from lizard-like side-to-side bending to mammal-like up-and-down bending. Early synapsids appear to have had relatively stiff spines, with later mammals evolving several kinds of regional movement and specialization.
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Mars lost substantial water to space, but that was not its only major fate. Isotope-constrained models indicate that ocean-scale amounts of ancient water could also have become locked into hydrated minerals in the crust, while some remains in ice and other reservoirs.
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Mars appears to have a smaller metallic core than first estimated by NASA's InSight mission. Newer analyses place the liquid core at roughly 1,650–1,675 km in radius, with a layer of molten silicate rock above it.
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Spacecraft imagery shows no artificial or geometrically straight canal network. Mars has natural valleys, channels, fractures, dunes, and evidence of ancient flowing water, but not the telescopic canal system once mapped.
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Mass and energy are related rather than completely separate. A body's rest mass corresponds to energy through E = mc², and energy stored inside a system contributes to that system's mass. Nuclear reactions make this connection large enough to measure easily.
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Systemic menopausal hormone therapy should not be started solely to prevent cardiovascular disease. Benefits and risks differ by age, time since menopause, formulation, route, dose, and whether a uterus is present.
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Mercury rotates three times for every two orbits around the Sun. It is in a 3:2 spin-orbit resonance, so every part of the planet experiences daylight over time.
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Metals are chemical elements or alloys whose properties arise from atomic structure, composition, crystal structure, bonding, defects, and microstructure. They are not built from universal sulfur and mercury principles.
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Meteor Crater formed about 50,000 years ago when an iron-nickel asteroid struck northern Arizona at high speed.
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The meter is defined through the speed of light and the second, not by the length of a stored object.
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Migraine is a neurological disorder involving brain networks, sensory processing, the trigeminal nerve system, signaling molecules, and blood vessels. Changes in vessel size can occur during an attack, but dilation by itself is neither necessary nor enough to explain migraine.
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The Milky Way is one galaxy among an enormous population of other galaxies spread throughout the observable universe.
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The Milky Way is our galaxy, a vast gravitationally bound system containing hundreds of billions of stars along with gas, dust, dark matter, and a central supermassive black hole.
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A future Milky Way–Andromeda merger remains plausible, but it is no longer considered inevitable. Simulations using newer Hubble and Gaia measurements, updated galaxy masses, and the gravitational influence of M33 and the Large Magellanic Cloud find roughly even odds that the two large galaxies will not merge within the next 10 billion years.
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Mitochondria and chloroplasts descend from bacteria that once lived independently. Ancient host cells took those bacteria inside, the partnership became permanent, and over evolutionary time the former bacteria became organelles—specialized structures inside the cell.
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Hundreds of molecular species have been detected in interstellar and circumstellar environments, including water, ammonia, alcohols, carbon chains, and complex organic molecules.
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The Moon is extremely dry compared with Earth, but it is not water-free. Small amounts of water and hydroxyl are bound in lunar minerals and volcanic glass, and water ice exists in some permanently shadowed regions near the poles.
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Chang’e-5 returned lunar basalts about 2 billion years old whose chemistry points to a mantle source with little KREEP contribution. KREEP—material rich in potassium, rare-earth elements, phosphorus, and heat-producing radioactive elements—is therefore not required as the direct source of the Moon’s youngest volcanism.
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Most major mountain belts form because tectonic plates move and interact. Continents can collide and thicken the crust, one plate can sink beneath another at a subduction zone, and faulting, volcanism, uplift, and erosion then shape the resulting mountains.
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Two independent 2025 studies concluded that Nanotyrannus represents a distinct tyrannosaur that lived alongside T. rex, using mature or nearly mature specimens to separate its anatomy from juvenile T. rex.
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Ionizing radiation can certainly mutate DNA, but at ordinary background levels its contribution to spontaneous mutation appears to be small. In a Lenski-style E. coli experiment beneath 1,700 m of rock, the absorbed dose rate fell from 214 to 26 nGy per hour, yet adaptation did not measurably slow over 500 generations. Replication errors and endogenous DNA chemistry provide abundant mutation sources even when ambient radiation is stripped away; ultra-low radiation can still affect cell physiology.
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Evolution can be measured over years or decades when traits are heritable and selection is strong. Rapid changes have been observed in microbes, insects, fish, birds, mammals, and humans.
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Neanderthals and modern humans interbred. Many people with ancestry outside sub-Saharan Africa carry roughly 1–2% Neanderthal-derived DNA, although each person carries a different collection of Neanderthal fragments.
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Neanderthals walked upright and had bodies adapted to cold climates. They made varied tools, controlled fire, hunted skillfully, cared for injured group members, and sometimes used ornaments or other symbolic objects.
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Nerves are bundles of neuronal axons that transmit information through electrochemical signaling, including membrane action potentials and neurotransmission at synapses.
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Neutrinos have a tiny but nonzero mass. They come in different types, called flavors, and can change from one flavor into another while traveling. That oscillation can occur only if the underlying neutrino states do not all have the same mass.
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Newborns have functional pain pathways and show hormonal, physiological, behavioral, and neurological responses to painful procedures. Pain relief is an important part of neonatal care.
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Noble gases are usually very unreactive, but some can form stable compounds. Xenon has the richest chemistry, and compounds involving krypton, radon, and argon are also known under suitable conditions.
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Fossils show that many non-avian dinosaurs had feathers or feather-like body coverings. Other dinosaur groups retained scales, and some had combinations of scales and feathers.
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Most human body cells contain 46 chromosomes, arranged in 23 pairs. Eggs and sperm normally contain 23.
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Oceanic crust is continuously created at mid-ocean ridges and destroyed at subduction zones, so it is generally much younger than continental crust. The oldest surviving ocean floor is only a small fraction of Earth's age.
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Most plant dry mass is carbon fixed from atmospheric carbon dioxide. Soil supplies water and essential mineral nutrients, but usually contributes only a small fraction of the dry matter added during growth.
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Most lunar craters were excavated by impacts from asteroids and comets. Volcanism created the dark maria and other features, but it did not produce the Moon's dominant crater population.
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Adult brains remain capable of change, a property known as neuroplasticity. Learning, experience, injury, stress, hormones, and rehabilitation can alter synapses, neural maps, connectivity, and even aspects of brain structure.
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Proteins are not the only molecules that can act as biological catalysts. Some RNA molecules can also speed up chemical reactions; these catalytic RNAs are called ribozymes.
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Some ocean regions contain plenty of major nutrients such as nitrate and phosphate but still support surprisingly little phytoplankton growth. In several of these regions, the missing ingredient is iron: tiny amounts of bioavailable iron can limit the microscopic algae that form the base of the food web.
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Ordinary optical microscopes cannot cleanly separate two nearby details once their blurred light patterns overlap below the diffraction limit. Super-resolution microscopy can recover finer information by changing how fluorescent molecules are switched on, measured, and reconstructed rather than by making conventional diffraction disappear.
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Organic molecules follow the same chemical principles as other matter and can be synthesized from nonliving starting materials. Laboratories and industry routinely make both natural and entirely new organic compounds.
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Oxidation does not require oxygen. In modern chemistry, oxidation means that a substance loses electrons, or equivalently that its oxidation state increases. Oxygen often causes oxidation, but chlorine, metal ions, and many other chemicals can do the same.
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Routine oxygen is not recommended for heart-attack patients who are not hypoxemic. Oxygen remains appropriate when saturation is low or respiratory distress is present.
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Primary pellagra is caused by severe deficiency of niacin (vitamin B3) or of tryptophan, an amino acid the body can use to make niacin. It can also develop when illness or medication interferes with absorption or metabolism.
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Most peptic ulcers are caused either by infection with Helicobacter pylori, a bacterium that can live in the stomach, or by nonsteroidal anti-inflammatory drugs (NSAIDs), a common class of pain-relief medicines that can damage the stomach and duodenal lining.
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After an uncomplicated heart attack, patients are usually mobilized much earlier. Carefully prescribed activity and cardiac rehabilitation improve recovery and help prevent the harms of prolonged immobility.
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Piltdown Man was a manufactured fraud assembled from human skull fragments and an orangutan jaw. The teeth were filed and the pieces artificially stained.
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The pituitary is an endocrine gland that releases hormones regulating growth, reproduction, stress responses, thyroid and adrenal function, water balance, and other processes. It is not a drainage route for brain mucus.
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The placenta is a selective exchange organ, not an impermeable wall. It allows oxygen and nutrients to reach the fetus and waste products to leave, but many medicines, alcohol, environmental chemicals, antibodies, and some infections can also cross it or affect its function.
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Disease arises through biological, genetic, environmental, behavioral, nutritional, toxic, traumatic, and social mechanisms. Planetary positions and zodiacal configurations do not exert clinically meaningful causal effects on disease or determine appropriate treatment.
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Planets and smaller bodies move through space under gravity and inertia; no solid or crystalline shells carry them around Earth.
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Planets move around the Sun in ellipses, with the Sun at one focus. Many planetary orbits are nearly circular, but they are not required to be perfect circles.
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Plants reproduce sexually as well as asexually. In seed plants, pollen carries the male reproductive cells, and fertilization occurs when sperm ultimately reaches the egg in an ovule, producing an embryo.
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Pluto is much smaller than Mercury and smaller than Earth's Moon, with a diameter of about 2,377 kilometers.
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Under the International Astronomical Union's 2006 definition, Pluto is a dwarf planet because it has not cleared the neighbourhood around its orbit. The Solar System has eight objects formally classified as planets.
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Most common polymers are electrical insulators, but some can conduct. Conjugated polymers have chains in which electrons can spread across connected bonds, and chemical doping can add or remove charge carriers and raise their conductivity dramatically.
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Predators can regulate dominant competitors, alter prey behavior, sustain species diversity, and trigger effects across food webs. Removing a key predator can simplify or reorganize an ecosystem rather than merely increasing prey abundance.
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Lobotomy causes irreversible brain injury and can produce profound changes in personality, motivation, cognition, continence, seizure risk, disability, and death. It has been abandoned as routine psychiatric treatment.
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Congenital anomalies arise from genetic, chromosomal, developmental, infectious, environmental, nutritional, metabolic, or other biological causes. A mother's visual impressions or imagination do not imprint corresponding physical shapes or marks on the fetus.
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Routine activity restriction has not been shown to prevent preterm birth and can cause deconditioning, bone loss, psychosocial harm, financial disruption, and increased risk of blood clots.
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Cells without a nucleus are not all one kind of organism. They include Bacteria and Archaea, two deeply different evolutionary lineages. Archaea can resemble bacteria under a microscope but differ in their cell membranes, genes, and much of the molecular machinery inside the cell.
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Pus usually indicates an inflammatory response to infection or tissue destruction. Modern wound care aims to prevent or control infection rather than encourage suppuration.
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“Protist” is a useful informal label for many eukaryotes that are not animals, plants, or fungi, but protists do not form one natural evolutionary branch. Different organisms once placed in Protista belong to several widely separated lineages.
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Protons and neutrons are not fundamental particles. They are composite particles built from quarks and gluons, whose interactions are governed by the strong nuclear force. Much of a proton or neutron's mass comes from the energy of this internal activity rather than simply from the masses of its quarks.
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Some pterosaurs had already reached wingspans above about 2.5 metres by the Middle Jurassic. The later Cretaceous still produced the largest pterosaurs, but large size began earlier than the older model suggested.
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Puerperal fever is usually a bacterial infection. Doctors and other medical staff can carry infectious material between patients, making hand hygiene a basic part of infection prevention.
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Quasars are not stars. They are extraordinarily bright active galactic nuclei—the compact centers of distant galaxies—powered by matter falling toward supermassive black holes.
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Radioactivity originates in unstable atomic nuclei. Ordinary changes in temperature, pressure, or chemical bonding generally have little or no effect on nuclear decay rates.
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Nuclear reactions can produce unstable isotopes that remain radioactive after bombardment stops. Artificial radionuclides are now made for research, medicine, industry, and energy applications.
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Insulin-coma therapy has no established specific benefit for schizophrenia and carries risks including seizures, prolonged coma, brain injury, metabolic complications, and death.
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X-rays are ionizing radiation: they carry enough energy to remove electrons from atoms and can therefore damage tissue and DNA. Radiation dose accumulates across exposures, although the risk from an individually justified modern diagnostic examination is usually small compared with its clinical benefit.
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Rogue waves are real, rare ocean waves that are much larger than the surrounding sea state. They can arise through nonlinear interactions, current focusing, directional effects, and ordinary statistical extremes.
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Respiratory particles form a continuous range of sizes rather than two clean categories separated by one universal cutoff. Larger particles tend to settle faster and smaller ones tend to remain airborne longer, but their behavior also depends on evaporation, airflow, humidity, and how they are produced.
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Most nutritional rickets results from inadequate vitamin D, calcium, or phosphate. These shortages impair bone mineralization—the hardening of growing bone with calcium- and phosphate-rich mineral. Limited sunlight, diet, malabsorption, and some inherited disorders can all contribute.
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Many viruses use RNA genomes, and RNA molecules can store, copy, and transmit hereditary information. Cellular organisms use DNA as their principal long-term genome, but heredity is not chemically restricted to DNA.
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RNA does much more than carry instructions from DNA to protein. Different RNA molecules can form part of the ribosome, catalyze chemical reactions, regulate genes, process other RNAs, help defend genomes, and in some viruses serve as the genetic material itself.
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Routine episiotomy does not provide those broad benefits and can increase pain, blood loss, healing problems, and serious perineal injury. Restrictive use produces better outcomes for most spontaneous vaginal births.
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Polymers are macromolecules: very large molecules made from many smaller building blocks joined by covalent bonds into long chains or networks. Materials such as rubber and cellulose are not merely loose clusters of ordinary small molecules.
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All four giant planets in our solar system have rings. Jupiter, Uranus, and Neptune have much fainter systems than Saturn.
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Saturn is the sixth planet from the Sun. Uranus and Neptune orbit farther out, along with many trans-Neptunian dwarf planets and smaller bodies.
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Saturn's rings consist of enormous numbers of independently orbiting particles, mostly water ice, ranging from dust-sized grains to large blocks and embedded moonlets.
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Schizophrenia is a complex disorder involving genetic vulnerability, brain development, biology, and environmental risk factors. Family relationships do not create the disorder.
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Scurvy is caused by severe vitamin C deficiency. Vitamin C is required for collagen synthesis and other biological functions, and adequate dietary intake prevents and cures the disease.
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Sponges are animals. They filter water through specialized cells, digest food internally, produce swimming larvae, and share ancestry with other animals.
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Mars has no confirmed surface vegetation. Seasonal and long-term albedo changes are produced mainly by dust movement, frost, winds, and exposed darker ground.
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Human footprints at White Sands, New Mexico, date to roughly 23,000–21,000 years ago, placing people in North America during the Last Glacial Maximum.
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Longitude can be determined by comparing local time with a reference time carried aboard ship or transmitted by radio or satellite systems.
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Sleep is an actively regulated, highly organized state with recurring non-REM and REM stages, distinct neural activity patterns, and multiple physiological functions.
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Slime molds are not true fungi. The name covers several groups of amoeba-like eukaryotes that crawl and feed as individual cells or moving masses before producing spore-bearing structures that happen to resemble fungal fruiting bodies.
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Some moons are highly geologically active. Io has intense volcanism; Europa and Enceladus contain subsurface oceans and show active ice deformation or plumes. Tidal heating from their planets can continually flex these moons and generate internal heat.
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Fossils are preserved remains, impressions, traces, or other evidence of past life. They typically form when organisms or traces are buried and preserved in sediment, sometimes with later mineral replacement.
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Interstellar space contains an extremely thin interstellar medium: gas, plasma, dust, molecules, cosmic rays, and magnetic fields. Denser molecular clouds are the raw material for new stars and planets.
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Populations evolve across generations, species share common ancestry, and new species can arise when populations diverge genetically and reproductively.
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Graphene—a sheet of carbon only one atom thick—and many other two-dimensional materials can exist as stable, free-standing or supported layers only one atomic layer thick.
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Some free radicals are sufficiently persistent to be prepared, stored, crystallized, and studied. Their stability can result from resonance, steric protection, electronic effects, or delocalization of the unpaired electron across the molecule.
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Traditional laboratory culture—growing microorganisms under controlled conditions—recovers only a fraction of environmental microbes. Many require unusual nutrients, partner organisms, host cells, slow growth, low nutrient levels, or conditions that are difficult to reproduce.
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Stars form, change structure and luminosity over time, and end in mass-dependent final states. Stellar classes occupy different stages and tracks of stellar evolution rather than being permanently fixed kinds.
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Most ordinary stars are made overwhelmingly of hydrogen and helium, not an Earth-like mixture of heavy elements. Elements such as iron, calcium, and oxygen are present in much smaller proportions, and their abundances vary between stars.
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Stonehenge was constructed in stages by Neolithic and Bronze Age communities, with the principal stone settings raised around 2500 BCE. Historically documented Druids lived much later.
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Meteorites are solid extraterrestrial objects that survive passage through the atmosphere and reach Earth's surface. Their origins include asteroids, the Moon, and Mars.
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The Sun is powered by nuclear fusion. In its core, hydrogen nuclei combine to form helium, converting a small amount of mass into energy.
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The Sun lies in the Milky Way's disk, roughly 26,000 light-years from the galactic center, and takes about 240 million years to complete one orbit.
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Gravitational contraction helped heat the young Sun, but the present Sun is powered mainly by nuclear fusion in its core.
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The Sun's corona, its thin outer atmosphere, reaches roughly one to several million kelvin—far hotter than the visible surface below, which is about 5,800 K. The corona is extremely thin, so high temperature does not mean it contains more total heat than the denser layers beneath it.
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Many conventional superconductors require very low temperatures, but copper-oxide and other unconventional materials remain superconducting at far higher temperatures, including above the boiling point of liquid nitrogen.
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After a heart attack, eliminating premature ventricular beats on an ECG does not necessarily make a patient safer. In the CAST trial, the drugs encainide and flecainide suppressed these abnormal beats but increased deaths from arrhythmia and increased overall mortality.
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Barn Swallows and related migratory swallows travel seasonally between breeding and wintering regions, sometimes covering thousands of kilometers. They do not spend winter submerged in mud.
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A synapse is the junction where one nerve cell communicates with another cell. At most vertebrate synapses, the first cell releases chemical messengers called neurotransmitters, which bind to receptors on the next cell. Some synapses are genuinely electrical and pass current directly between cells through connecting channels.
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Thalidomide is a powerful human teratogen. Exposure during sensitive stages of early pregnancy can cause severe limb, ear, eye, cardiac, and internal-organ defects, and pregnancy must be rigorously prevented during treatment.
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A projectile does not require a continuing forward-moving agent. Inertia carries it forward while gravity, aerodynamic drag, and other forces change its motion.
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Lightning is a large electrical discharge produced after charge separation creates sufficiently strong electric fields within storms or between clouds and the ground. Thunder is the acoustic shock produced by rapid heating and expansion along the lightning channel.
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The thymus is a training and selection site for developing T cells, immune cells that help coordinate and carry out targeted immune responses. It helps preserve cells that can respond to threats while eliminating or restraining many that react strongly against the body's own tissues. Its activity declines with age but does not become meaningless.
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Elapsed time depends on relative motion and gravitational conditions. Observers can disagree about the duration and simultaneity of events while each obtains internally consistent measurements.
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Titan is slowly moving away from Saturn, but much faster than older tidal models predicted for such a distant moon. Cassini measurements support a process called resonance locking, in which Titan can remain strongly coupled to changing oscillations inside Saturn and continue receiving tidal energy.
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Secondhand smoke causes lung cancer, coronary heart disease, and stroke in adults who do not smoke, and causes serious respiratory and developmental harms in infants and children. No risk-free exposure level has been identified.
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Prions are infectious agents made mainly of protein and carry no DNA or RNA genome of their own. A misfolded prion protein can force normally folded copies of the same protein in the host to change into the same abnormal shape, allowing the harmful form to spread.
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Tuberculosis is caused by infection with Mycobacterium tuberculosis. Genetics and immune function affect who becomes infected or develops disease, but the bacterium is the necessary cause.
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Different compounds can share a molecular formula while differing in atom connectivity or three-dimensional arrangement. These isomers can have very different physical, chemical, and biological properties.
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The universe is expanding on large scales. Distant galaxies generally recede in a relationship between their distance and redshift, and the expansion rate has changed over cosmic time.
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Healthy bladders can contain low-biomass microbial communities. Detecting bacteria does not by itself establish a urinary tract infection.
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Mutations arise through biochemical processes without foreknowledge of which changes will be useful. Selection then increases variants that happen to improve survival or reproduction in a particular environment.
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During repeated Pleistocene glaciations, continental ice sheets thousands of meters thick covered much of northern North America and Eurasia.
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Earth's continents are products of plate tectonics and geological history; there is no physical requirement for land area to be symmetrically balanced between hemispheres. Antarctica exists, but it is not the enormous temperate Terra Australis imagined on early maps.
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Venus has a dry, hostile surface with temperatures around 465°C and pressures about 90 times Earth's sea-level pressure.
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Some giant viruses have particles as large as small bacteria and genomes containing more than a million base pairs and hundreds of genes.
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Light from external sources is emitted or reflected by objects, enters the eye, is focused onto the retina, and is converted by photoreceptors into neural signals processed by the visual system.
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Volcanoes are driven by molten rock and expanding gases, not by underground fires. Magma forms within Earth and can rise because it is buoyant. As pressure falls during ascent, dissolved gases come out of the magma and expand, sometimes powering explosive eruptions.
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Hotspots are relatively stable compared with moving plates, but some can migrate, interact with mantle flow, or change position. Different hotspots do not define one perfectly rigid reference frame.
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The deep ocean participates in slow, global circulation driven by density differences, winds, mixing, and interactions with the seafloor and atmosphere.
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Water is a chemical compound with the formula H2O. It can be formed from hydrogen and oxygen and can be decomposed into those elements.
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White light can contain a mixture of wavelengths. A prism separates different wavelengths because the refractive index depends on wavelength; it does not manufacture the spectral colors from otherwise colorless light.
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The Yamnaya were mobile pastoralist communities of the Pontic-Caspian steppe whose ancestry spread widely into Europe around 3000 BCE. Ancient horse genomes place the rapid spread of the lineage that dominates modern domestic horses around 2200 BCE, several centuries later, so large domestic-horse herds cannot explain the earlier expansion in the form once proposed.
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Fire can be destructive, especially when unusually severe or threatening people, but it is also a recurring ecological process in many forests, grasslands, shrublands, and wetlands. Numerous species and ecosystems are adapted to particular fire frequencies, seasons, and intensities.
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During pecking, the woodpecker head behaves mainly as a stiff hammer rather than a shock absorber. Its small brain and cranial geometry help keep predicted pressures below damaging levels without substantially dissipating the impact.
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Water stored in weathered and fractured bedrock can be a routine part of the water supply for trees and shrubs, not just an emergency reserve during severe drought. Its importance varies with geology, climate and rooting depth.
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Many wounds heal faster in a protected, appropriately moist environment. Moisture supports cell migration and tissue repair, while excessive dryness can slow healing.
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Yellow fever is a viral disease spread mainly by infected mosquitoes. In urban transmission, Aedes aegypti is the principal mosquito vector; contaminated clothing, bedding, and ordinary contact with patients are not the main route.
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