User:Armanaziz/Nature

Introduction

Selected general articles

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  An example of the biodiversity of fungi in a forest in North Saskatchewan (in this photo, there are also leaf lichens and mosses).

  
  
  Biodiversity is the variability of life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and phylogenetic diversity. Diversity is not distributed evenly on Earth. It is greater in the tropics as a result of the warm climate and high primary productivity in the region near the equator. Tropical forest ecosystems cover less than one-fifth of Earth's terrestrial area and contain about 50% of the world's species. There are latitudinal gradients in species diversity for both marine and terrestrial taxa.
  
  Since life began on Earth, six major mass extinctions and several minor events have led to large and sudden drops in biodiversity. The Phanerozoic aeon (the last 540 million years) marked a rapid growth in biodiversity via the Cambrian explosion. In this period, the majority of multicellular phyla first appeared. The next 400 million years included repeated, massive biodiversity losses. Those events have been classified as mass extinction events. In the Carboniferous, rainforest collapse may have led to a great loss of plant and animal life. The Permian–Triassic extinction event, 251 million years ago, was the worst; vertebrate recovery took 30 million years.
  
  Human activities have led to an ongoing biodiversity loss and an accompanying loss of genetic diversity. This process is often referred to as Holocene extinction, or sixth mass extinction. For example, it was estimated in 2007 that up to 30% of all species will be extinct by 2050. Destroying habitats for farming is a key reason why biodiversity is decreasing today. Climate change also plays a role. This can be seen for example in the effects of climate change on biomes. This anthropogenic extinction may have started toward the end of the Pleistocene, as some studies suggest that the megafaunal extinction event that took place around the end of the last ice age partly resulted from overhunting. (Full article...)
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  Examples of protists. Clockwise from top left: red algae, kelp, ciliate, golden alga, dinoflagellate, metamonad, amoeba, slime mold.

  
  A protist (/ˈproʊtɪst/ PROH-tist) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a polyphyletic grouping of several independent clades that evolved from the last eukaryotic common ancestor.
  
  Protists were historically regarded as a separate taxonomic kingdom known as Protista or Protoctista. With the advent of phylogenetic analysis and electron microscopy studies, the use of Protista as a formal taxon was gradually abandoned. In modern classifications, protists are spread across several eukaryotic clades called supergroups, such as Archaeplastida (photoautotrophs that includes land plants), SAR, Obazoa (which includes fungi and animals), Amoebozoa and Excavata.
  
  Protists represent an extremely large genetic and ecological diversity in all environments, including extreme habitats. Their diversity, larger than for all other eukaryotes, has only been discovered in recent decades through the study of environmental DNA and is still in the process of being fully described. They are present in all ecosystems as important components of the biogeochemical cycles and trophic webs. They exist abundantly and ubiquitously in a variety of forms that evolved multiple times independently, such as free-living algae, amoebae and slime moulds, or as important parasites. Together, they compose an amount of biomass that doubles that of animals. They exhibit varied types of nutrition (such as phototrophy, phagotrophy or osmotrophy), sometimes combining them (in mixotrophy). They present unique adaptations not present in multicellular animals, fungi or land plants. The study of protists is termed protistology. (Full article...)
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  Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not begin until the 18th century. The 19th century saw modest progress in the field after weather observation networks were formed across broad regions. Prior attempts at prediction of weather depended on historical data. It was not until after the elucidation of the laws of physics, and more particularly in the latter half of the 20th century, the development of the computer (allowing for the automated solution of a great many modelling equations) that significant breakthroughs in weather forecasting were achieved. An important branch of weather forecasting is marine weather forecasting as it relates to maritime and coastal safety, in which weather effects also include atmospheric interactions with large bodies of water.
  
  Meteorological phenomena are observable weather events that are explained by the science of meteorology. Meteorological phenomena are described and quantified by the variables of Earth's atmosphere: temperature, air pressure, water vapour, mass flow, and the variations and interactions of these variables, and how they change over time. Different spatial scales are used to describe and predict weather on local, regional, and global levels.
  
  Meteorology, climatology, atmospheric physics, and atmospheric chemistry are sub-disciplines of the atmospheric sciences. Meteorology and hydrology compose the interdisciplinary field of hydrometeorology. The interactions between Earth's atmosphere and its oceans are part of a coupled ocean-atmosphere system. Meteorology has application in many diverse fields such as the military, energy production, transport, agriculture, and construction. (Full article...)
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  Blue light is scattered more than other wavelengths by the gases in the atmosphere, surrounding Earth in a visibly blue layer at the stratosphere, above the clouds of the troposphere, when seen from space on board the ISS at an altitude of 335 km (208 mi) (the Moon is visible as a crescent in the far background).

  
  The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weather features such as clouds and hazes), all retained by Earth's gravity. The atmosphere serves as a protective buffer between the Earth's surface and outer space, shields the surface from most meteoroids and ultraviolet solar radiation, keeps it warm and reduces diurnal temperature variation (temperature extremes between day and night) through heat retention (greenhouse effect), redistributes heat and moisture among different regions via air currents, and provides the chemical and climate conditions allowing life to exist and evolve on Earth.
  
  By mole fraction (i.e., by quantity of molecules), dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other trace gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere. Air composition, temperature and atmospheric pressure vary with altitude. Within the atmosphere, air suitable for use in photosynthesis by terrestrial plants and respiration of terrestrial animals is found only within 12 kilometres (7.5 mi) from the ground.
  
  Earth's early atmosphere consisted of accreted gases from the solar nebula, but the atmosphere changed significantly over time, affected by many factors such as volcanism, impact events, weathering and the evolution of life (particularly the photoautotrophs). Recently, human activity has also contributed to atmospheric changes, such as climate change (mainly through deforestation and fossil fuel-related global warming), ozone depletion and acid deposition. (Full article...)
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  Clockwise from top left:

  • Amanita muscaria, a basidiomycete;
  • Sarcoscypha coccinea, an ascomycete;
  • bread covered in mold;
  • a chytrid;
  • an Aspergillus conidiophore.

  
  
  

  
  A fungus (pl.: fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as one of the traditional eukaryotic kingdoms, along with Animalia, Plantae, and either Protista or Protozoa and Chromista.
  
  A characteristic that places fungi in a different kingdom from plants, bacteria, and some protists is chitin in their cell walls. Fungi, like animals, are heterotrophs; they acquire their food by absorbing dissolved molecules, typically by secreting digestive enzymes into their environment. Fungi do not photosynthesize. Growth is their means of mobility, except for spores (a few of which are flagellated), which may travel through the air or water. Fungi are the principal decomposers in ecological systems. These and other differences place fungi in a single group of related organisms, named the Eumycota (true fungi or Eumycetes), that share a common ancestor (i.e. they form a monophyletic group), an interpretation that is also strongly supported by molecular phylogenetics. This fungal group is distinct from the structurally similar myxomycetes (slime molds) and oomycetes (water molds). The discipline of biology devoted to the study of fungi is known as mycology (from the Greek μύκης mykes, mushroom). In the past, mycology was regarded as a branch of botany, although it is now known that fungi are genetically more closely related to animals than to plants.
  
  Abundant worldwide, most fungi are inconspicuous because of the small size of their structures, and their cryptic lifestyles in soil or on dead matter. Fungi include symbionts of plants, animals, or other fungi and also parasites. They may become noticeable when fruiting, either as mushrooms or as molds. Fungi perform an essential role in the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange in the environment. They have long been used as a direct source of human food, in the form of mushrooms and truffles; as a leavening agent for bread; and in the fermentation of various food products, such as wine, beer, and soy sauce. Since the 1940s, fungi have been used for the production of antibiotics, and, more recently, various enzymes produced by fungi are used industrially and in detergents. Fungi are also used as biological pesticides to control weeds, plant diseases, and insect pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, that are toxic to animals, including humans. The fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies. Fungi can break down manufactured materials and buildings, and become significant pathogens of humans and other animals. Losses of crops due to fungal diseases (e.g., rice blast disease) or food spoilage can have a large impact on human food supplies and local economies. (Full article...)
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  Biology is the science of life. It spans multiple levels from biomolecules and cells to organisms and populations.

  
  Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of at least one cell that processes hereditary information encoded in genes, which can be transmitted to future generations. Another major theme is evolution, which explains the unity and diversity of life. Energy processing is also important to life as it allows organisms to move, grow, and reproduce. Finally, all organisms are able to regulate their own internal environments.
  
  Biologists are able to study life at multiple levels of organization, from the molecular biology of a cell to the anatomy and physiology of plants and animals, and evolution of populations. Hence, there are multiple subdisciplines within biology, each defined by the nature of their research questions and the tools that they use. Like other scientists, biologists use the scientific method to make observations, pose questions, generate hypotheses, perform experiments, and form conclusions about the world around them.
  
  Life on Earth, which emerged more than 3.7 billion years ago, is immensely diverse. Biologists have sought to study and classify the various forms of life, from prokaryotic organisms such as archaea and bacteria to eukaryotic organisms such as protists, fungi, plants, and animals. These various organisms contribute to the biodiversity of an ecosystem, where they play specialized roles in the cycling of nutrients and energy through their biophysical environment. (Full article...)
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  Simplified schematic of an island's flora – all its plant species, highlighted in boxes

  
  Flora (pl.: floras or florae) is all the plant life present in a particular region or time, generally the naturally occurring (indigenous) native plants. The corresponding term for animals is fauna, and for fungi, it is funga. Sometimes bacteria and fungi are also referred to as flora as in the terms gut flora or skin flora. (Full article...)
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  The study of planetary habitability is partly based upon extrapolation from knowledge of the Earth's conditions, as the Earth is the only planet currently known to harbour life (The Blue Marble, 1972 Apollo 17 photograph).

  
  The Gaia hypothesis (/ˈɡaɪ.ə/), also known as the Gaia theory, Gaia paradigm, or the Gaia principle, proposes that living organisms interact with their inorganic surroundings on Earth to form a synergistic and self-regulating complex system that helps to maintain and perpetuate the conditions for life on the planet.
  
  The Gaia hypothesis was formulated by the chemist James Lovelock and co-developed by the microbiologist Lynn Margulis in the 1970s. Following the suggestion by his neighbour, novelist William Golding, Lovelock named the hypothesis after Gaia, the primordial deity who personified the Earth in Greek mythology. In 2006, the Geological Society of London awarded Lovelock the Wollaston Medal in part for his work on the Gaia hypothesis.
  
  Topics related to the hypothesis include how the biosphere and the evolution of organisms affect the stability of global temperature, salinity of seawater, atmospheric oxygen levels, the maintenance of a hydrosphere of liquid water and other environmental variables that affect the habitability of Earth. (Full article...)
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  A right-handed three-dimensional Cartesian coordinate system used to indicate positions in space

  
  
  Space is a three-dimensional continuum containing positions and directions. In classical physics, physical space is often conceived in three linear dimensions. Modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as spacetime. The concept of space is considered to be of fundamental importance to an understanding of the physical universe. However, disagreement continues between philosophers over whether it is itself an entity, a relationship between entities, or part of a conceptual framework.
  
  In the 19th and 20th centuries mathematicians began to examine geometries that are non-Euclidean, in which space is conceived as curved, rather than flat, as in the Euclidean space. According to Albert Einstein's theory of general relativity, space around gravitational fields deviates from Euclidean space. Experimental tests of general relativity have confirmed that non-Euclidean geometries provide a better model for the shape of space. (Full article...)
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  Time is the continuous progression of our changing existence that occurs in an apparently irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequence events, to compare the duration of events (or the intervals between them), and to quantify rates of change of quantities in material reality or in the conscious experience. Time is often referred to as a fourth dimension, along with three spatial dimensions. Scientists have theorized a beginning of time in our universe (the Big Bang) and an end (e.g., heat death or the Big Crunch). A cyclic model describes a cyclical nature, whereas the philosophy of eternalism views the subject from a different angle.
  
  Time is one of the seven fundamental physical quantities in both the International System of Units (SI) and International System of Quantities. The SI base unit of time is the second, which is defined by measuring the electronic transition frequency of caesium atoms. General relativity is the primary framework for understanding how spacetime works. Through advances in both theoretical and experimental investigations of spacetime, it has been shown that time can be distorted and dilated, particularly at the edges of black holes.
  
  Throughout history, time has been an important subject of study in religion, philosophy, and science. Temporal measurement has occupied scientists and technologists and has been a prime motivation in navigation and astronomy. Time is also of significant social importance, having economic value ("time is money") as well as personal value, due to an awareness of the limited time in each day and in human life spans. Cultural attitudes towards the human use of time are apparent in the verbs used—from "kill" to "waste" to "pass"—and sayings (like carpe diem). (Full article...)
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  Illustration of the relative abilities of three different types of ionizing radiation to penetrate solid matter. Typical alpha particles (α) are stopped by a sheet of paper, while beta particles (β) are stopped by 3mm aluminum foil. Gamma radiation (γ) is dampened when it penetrates lead. Note caveats in the text about this simplified diagram.

  
  
  In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes:

  • electromagnetic radiation consisting of photons, such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma radiation (γ)
  • particle radiation consisting of particles of non-zero rest energy, such as alpha radiation (α), beta radiation (β), proton radiation and neutron radiation
  • acoustic radiation, such as ultrasound, sound, and seismic waves, all dependent on a physical transmission medium
  • gravitational radiation, in the form of gravitational waves, ripples in spacetime

  
  
  Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. Ionizing radiation carries more than 10 electron volts (eV), which is enough to ionize atoms and molecules and break chemical bonds. This is an important distinction due to the large difference in harmfulness to living organisms. A common source of ionizing radiation is radioactive materials that emit α, β, or γ radiation, consisting of helium nuclei, electrons or positrons, and photons, respectively. Other sources include X-rays from medical radiography examinations and muons, mesons, positrons, neutrons and other particles that constitute the secondary cosmic rays that are produced after primary cosmic rays interact with Earth's atmosphere.
  
  Gamma rays, X-rays, and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum. The word "ionize" refers to the breaking of one or more electrons away from an atom, an action that requires the relatively high energies that these electromagnetic waves supply. Further down the spectrum, the non-ionizing lower energies of the lower ultraviolet spectrum cannot ionize atoms, but can disrupt the inter-atomic bonds that form molecules, thereby breaking down molecules rather than atoms; a good example of this is sunburn caused by long-wavelength solar ultraviolet. The waves of longer wavelength than UV in visible light, infrared, and microwave frequencies cannot break bonds but can cause vibrations in the bonds which are sensed as heat. Radio wavelengths and below generally are not regarded as harmful to biological systems. These are not sharp delineations of the energies; there is some overlap in the effects of specific frequencies. (Full article...)
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  Biological organisation is the organisation of complex biological structures and systems that define life using a reductionistic approach. The traditional hierarchy, as detailed below, extends from atoms to biospheres. The higher levels of this scheme are often referred to as an ecological organisation concept, or as the field, hierarchical ecology.
  
  Each level in the hierarchy represents an increase in organisational complexity, with each "object" being primarily composed of the previous level's basic unit. The basic principle behind the organisation is the concept of emergence—the properties and functions found at a hierarchical level are not present and irrelevant at the lower levels.
  
  The biological organisation of life is a fundamental premise for numerous areas of scientific research, particularly in the medical sciences. Without this necessary degree of organisation, it would be much more difficult—and likely impossible—to apply the study of the effects of various physical and chemical phenomena to diseases and physiology (body function). For example, fields such as cognitive and behavioral neuroscience could not exist if the brain was not composed of specific types of cells, and the basic concepts of pharmacology could not exist if it was not known that a change at the cellular level can affect an entire organism. These applications extend into the ecological levels as well. For example, DDT's direct insecticidal effect occurs at the subcellular level, but affects higher levels up to and including multiple ecosystems. Theoretically, a change in one atom could change the entire biosphere. (Full article...)
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  Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorological variables that are commonly measured are temperature, humidity, atmospheric pressure, wind, and precipitation. In a broader sense, climate is the state of the components of the climate system, including the atmosphere, hydrosphere, cryosphere, lithosphere and biosphere and the interactions between them. The climate of a location is affected by its latitude, longitude, terrain, altitude, land use and nearby water bodies and their currents.
  
  Climates can be classified according to the average and typical variables, most commonly temperature and precipitation. The most widely used classification scheme is the Köppen climate classification. The Thornthwaite system, in use since 1948, incorporates evapotranspiration along with temperature and precipitation information and is used in studying biological diversity and how climate change affects it. The major classifications in Thornthwaite's climate classification are microthermal, mesothermal, and megathermal. Finally, the Bergeron and Spatial Synoptic Classification systems focus on the origin of air masses that define the climate of a region.
  
  Paleoclimatology is the study of ancient climates. Paleoclimatologists seek to explain climate variations for all parts of the Earth during any given geologic period, beginning with the time of the Earth's formation. Since very few direct observations of climate were available before the 19th century, paleoclimates are inferred from proxy variables. They include non-biotic evidence—such as sediments found in lake beds and ice cores—and biotic evidence—such as tree rings and coral. Climate models are mathematical models of past, present, and future climates. Climate change may occur over long and short timescales due to various factors. Recent warming is discussed in terms of global warming, which results in redistributions of biota. For example, as climate scientist Lesley Ann Hughes has written: "a 3 °C [5 °F] change in mean annual temperature corresponds to a shift in isotherms of approximately 300–400 km [190–250 mi] in latitude (in the temperate zone) or 500 m [1,600 ft] in elevation. Therefore, species are expected to move upwards in elevation or towards the poles in latitude in response to shifting climate zones." (Full article...)
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  The chemical elements ordered in the periodic table

  
  A chemical element is a chemical substance whose atoms all have the same number of protons. The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8, meaning each oxygen atom has 8 protons in its nucleus. Atoms of the same element can have different numbers of neutrons in their nuclei, known as isotopes of the element. Two or more atoms can combine to form molecules. Some elements are formed from molecules of identical atoms, e. g. atoms of hydrogen (H) form diatomic molecules (H₂). Chemical compounds are substances made of atoms of different elements; they can have molecular or non-molecular structure. Mixtures are materials containing different chemical substances; that means (in case of molecular substances) that they contain different types of molecules. Atoms of one element can be transformed into atoms of a different element in nuclear reactions, which change an atom's atomic number.
  
  Historically, the term "chemical element" meant a substance that cannot be broken down into constituent substances by chemical reactions, and for most practical purposes this definition still has validity. There was some controversy in the 1920s over whether isotopes deserved to be recognized as separate elements if they could be separated by chemical means.
  
  The term "(chemical) element" is used in two different but closely related meanings: it can mean a chemical substance consisting of a single kind of atoms, or it can mean that kind of atoms as a component of various chemical substances. For example, molecules of water (H₂O) contain atoms of hydrogen (H) and oxygen (O), so water can be said as a compound consisting of the elements hydrogen (H) and oxygen (O) even though it does not contain the chemical substances (di)hydrogen (H₂) and (di)oxygen (O₂), as H₂O molecules are different from H₂ and O₂ molecules. For the meaning "chemical substance consisting of a single kind of atoms", the terms "elementary substance" and "simple substance" have been suggested, but they have not gained much acceptance in English chemical literature, whereas in some other languages their equivalent is widely used. For example, the French chemical terminology distinguishes élément chimique (kind of atoms) and corps simple (chemical substance consisting of a single kind of atoms); the Russian chemical terminology distinguishes химический элемент and простое вещество. (Full article...)
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  Map of Earth's 16 principal tectonic plates
  
  Divergent:

    Extension zone

  Convergent:

    Collision zone

  Transform:

    Sinistral transform

  
  Plate tectonics (from Latin tectonicus, from Ancient Greek τεκτονικός (tektonikós) 'pertaining to building') is the scientific theory that Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. Plate tectonics came to be accepted by geoscientists after seafloor spreading was validated in the mid-to-late 1960s. The processes that result in plates and shape Earth's crust are called tectonics.
  Tectonic plates also occur in other planets and moons.
  
  Earth's lithosphere, the rigid outer shell of the planet including the crust and upper mantle, is fractured into seven or eight major plates (depending on how they are defined) and many minor plates or "platelets". Where the plates meet, their relative motion determines the type of plate boundary (or fault): convergent, divergent, or transform. The relative movement of the plates typically ranges from zero to 10 cm annually. Faults tend to be geologically active, experiencing earthquakes, volcanic activity, mountain-building, and oceanic trench formation.
  
  Tectonic plates are composed of the oceanic lithosphere and the thicker continental lithosphere, each topped by its own kind of crust. Along convergent plate boundaries, the process of subduction carries the edge of one plate down under the other plate and into the mantle. This process reduces the total surface area (crust) of the Earth. The lost surface is balanced by the formation of new oceanic crust along divergent margins by seafloor spreading, keeping the total surface area constant in a tectonic "conveyor belt". (Full article...)
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  Pacific Ocean of Earth seen from space in 1969

  
  The ocean is the body of salt water that covers approximately 70.8% of Earth. In English, the term ocean also refers to any of the large bodies of water into which the world ocean is conventionally divided. The following names describe five different areas of the ocean: Pacific, Atlantic, Indian, Antarctic/Southern, and Arctic. The ocean contains 97% of Earth's water and is the primary component of Earth's hydrosphere and is thereby essential to life on Earth. The ocean influences climate and weather patterns, the carbon cycle, and the water cycle by acting as a huge heat reservoir.
  
  Ocean scientists split the ocean into vertical and horizontal zones based on physical and biological conditions. The pelagic zone is the open ocean's water column from the surface to the ocean floor. The water column is further divided into zones based on depth and the amount of light present. The photic zone starts at the surface and is defined to be "the depth at which light intensity is only 1% of the surface value" (approximately 200 m in the open ocean). This is the zone where photosynthesis can occur. In this process plants and microscopic algae (free floating phytoplankton) use light, water, carbon dioxide, and nutrients to produce organic matter. As a result, the photic zone is the most biodiverse and the source of the food supply which sustains most of the ocean ecosystem. Ocean photosynthesis also produces half of the oxygen in the Earth's atmosphere. Light can only penetrate a few hundred more meters; the rest of the deeper ocean is cold and dark (these zones are called mesopelagic and aphotic zones). The continental shelf is where the ocean meets dry land. It is more shallow, with a depth of a few hundred meters or less. Human activity often has negative impacts on marine life within the continental shelf.
  
  Ocean temperatures depend on the amount of solar radiation reaching the ocean surface. In the tropics, surface temperatures can rise to over 30 °C (86 °F). Near the poles where sea ice forms, the temperature in equilibrium is about −2 °C (28 °F). In all parts of the ocean, deep ocean temperatures range between −2 °C (28 °F) and 5 °C (41 °F). Constant circulation of water in the ocean creates ocean currents. Those currents are caused by forces operating on the water, such as temperature and salinity differences, atmospheric circulation (wind), and the Coriolis effect. Tides create tidal currents, while wind and waves cause surface currents. The Gulf Stream, Kuroshio Current, Agulhas Current and Antarctic Circumpolar Current are all major ocean currents. Such currents transport massive amounts of water, gases, pollutants and heat to different parts of the world, and from the surface into the deep ocean. All this has impacts on the global climate system. (Full article...)
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  A tornado approaching Elie, Manitoba, Canada in June 2007.

  
  A tornado is a violently rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the center around which, from an observer looking down toward the surface of the Earth, winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern. Tornadoes come in many shapes and sizes, and they are often (but not always) visible in the form of a condensation funnel originating from the base of a cumulonimbus cloud, with a cloud of rotating debris and dust beneath it. Most tornadoes have wind speeds less than 180 kilometers per hour (110 miles per hour), are about 80 meters (250 feet) across, and travel several kilometers (a few miles) before dissipating. The most extreme tornadoes can attain wind speeds of more than 480 kilometers per hour (300 mph), can be more than 3 kilometers (2 mi) in diameter, and can stay on the ground for more than 100 km (62 mi).
  
  Various types of tornadoes include the multiple-vortex tornado, landspout, and waterspout. Waterspouts are characterized by a spiraling funnel-shaped wind current, connecting to a large cumulus or cumulonimbus cloud. They are generally classified as non-supercellular tornadoes that develop over bodies of water, but there is disagreement over whether to classify them as true tornadoes. These spiraling columns of air frequently develop in tropical areas close to the equator and are less common at high latitudes. Other tornado-like phenomena that exist in nature include the gustnado, dust devil, fire whirl, and steam devil.
  
  Tornadoes occur most frequently in North America (particularly in central and southeastern regions of the United States colloquially known as Tornado Alley; the United States has by far the most tornadoes of any country in the world). Tornadoes also occur in South Africa, much of Europe (except most of the Alps), western and eastern Australia, New Zealand, Bangladesh and adjacent eastern India, Japan, the Philippines, and southeastern South America (Uruguay and Argentina). Tornadoes can be detected before or as they occur through the use of pulse-Doppler radar by recognizing patterns in velocity and reflectivity data, such as hook echoes or debris balls, as well as through the efforts of storm spotters. (Full article...)
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  Ecology (from Ancient Greek οἶκος (oîkos) 'house' and -λογία (-logía) 'study of') is the natural science of the relationships among living organisms and their environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere levels. Ecology overlaps with the closely related sciences of biogeography, evolutionary biology, genetics, ethology, and natural history.
  
  Ecology is a branch of biology, and is the study of abundance, biomass, and distribution of organisms in the context of the environment. It encompasses life processes, interactions, and adaptations; movement of materials and energy through living communities; successional development of ecosystems; cooperation, competition, and predation within and between species; and patterns of biodiversity and its effect on ecosystem processes.
  
  Ecology has practical applications in conservation biology, wetland management, natural resource management (agroecology, agriculture, forestry, agroforestry, fisheries, mining, tourism), urban planning (urban ecology), community health, economics, basic and applied science, and human social interaction (human ecology). (Full article...)
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  Angiosperm

  
  Plants are the eukaryotes that form the kingdom Plantae; they are predominantly photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with cyanobacteria to produce sugars from carbon dioxide and water, using the green pigment chlorophyll. Exceptions are parasitic plants that have lost the genes for chlorophyll and photosynthesis, and obtain their energy from other plants or fungi. Most plants are multicellular, except for some green algae.
  
  Historically, as in Aristotle's biology, the plant kingdom encompassed all living things that were not animals, and included algae and fungi. Definitions have narrowed since then; current definitions exclude the fungi and some of the algae. By the definition used in this article, plants form the clade Viridiplantae (green plants), which consists of the green algae and the embryophytes or land plants (hornworts, liverworts, mosses, lycophytes, ferns, conifers and other gymnosperms, and flowering plants). A definition based on genomes includes the Viridiplantae, along with the red algae and the glaucophytes, in the clade Archaeplastida.
  
  There are about 380,000 known species of plants, of which the majority, some 260,000, produce seeds. They range in size from single cells to the tallest trees. Green plants provide a substantial proportion of the world's molecular oxygen; the sugars they create supply the energy for most of Earth's ecosystems and other organisms, including animals, either eat plants directly or rely on organisms which do so. (Full article...)
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  An organism is any living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have been proposed to define what an organism is. Among the most common is that an organism has autonomous reproduction, growth, and metabolism. This would exclude viruses, despite the fact that they evolve like organisms. Other problematic cases include colonial organisms; a colony of eusocial insects is organised adaptively, and has germ-soma specialisation, with some insects reproducing, others not, like cells in an animal's body. The body of a siphonophore, a jelly-like marine animal, is composed of organism-like zooids, but the whole structure looks and functions much like an animal such as a jellyfish, the parts collaborating to provide the functions of the colonial organism.
  
  The evolutionary biologists David Queller and Joan Strassmann state that "organismality", the qualities or attributes that define an entity as an organism, has evolved socially as groups of simpler units (from cells upwards) came to cooperate without conflicts. They propose that cooperation should be used as the "defining trait" of an organism. This would treat many types of collaboration, including the fungus/alga partnership of different species in a lichen, or the permanent sexual partnership of an anglerfish, as an organism. (Full article...)
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  Conjectured illustration of the scorched Earth after the Sun has entered the red giant phase, about 5–7 billion years from now

  
  
  The biological and geological future of Earth can be extrapolated based on the estimated effects of several long-term influences. These include the chemistry at Earth's surface, the cooling rate of the planet's interior, the gravitational interactions with other objects in the Solar System, and a steady increase in the Sun's luminosity. An uncertain factor is the pervasive influence of technology introduced by humans, such as climate engineering, which could cause significant changes to the planet. For example, the current Holocene extinction is being caused by technology, and the effects may last for up to five million years. In turn, technology may result in the extinction of humanity, leaving the planet to gradually return to a slower evolutionary pace resulting solely from long-term natural processes.
  
  Over time intervals of hundreds of millions of years, random celestial events pose a global risk to the biosphere, which can result in mass extinctions. These include impacts by comets or asteroids and the possibility of a near-Earth supernova—a massive stellar explosion within a 100-light-year (31-parsec) radius of the Sun. Other large-scale geological events are more predictable. Milankovitch's theory predicts that the planet will continue to undergo glacial periods at least until the Quaternary glaciation comes to an end. These periods are caused by the variations in eccentricity, axial tilt, and precession of Earth's orbit. As part of the ongoing supercontinent cycle, plate tectonics will probably result in a supercontinent in 250–350 million years. Sometime in the next 1.5–4.5 billion years, Earth's axial tilt may begin to undergo chaotic variations, with changes in the axial tilt of up to 90°.
  
  The luminosity of the Sun will steadily increase, causing a rise in the solar radiation reaching Earth and resulting in a higher rate of weathering of silicate minerals. This will affect the carbonate–silicate cycle, which will cause a decrease in the level of carbon dioxide in the atmosphere. In about 600 million years from now, the level of carbon dioxide will fall below the level needed to sustain C₃ carbon fixation photosynthesis used by trees. Some plants use the C₄ carbon fixation method to persist at carbon dioxide concentrations as low as ten parts per million. However, the long-term trend is for plant life to die off altogether. The extinction of plants will be the demise of almost all animal life since plants are the base of much of the animal food chain on Earth. (Full article...)
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  Calculus is the mathematical study of continuous change, in the same way that geometry is the study of shape, and algebra is the study of generalizations of arithmetic operations.
  
  Originally called infinitesimal calculus or "the calculus of infinitesimals", it has two major branches, differential calculus and integral calculus. The former concerns instantaneous rates of change, and the slopes of curves, while the latter concerns accumulation of quantities, and areas under or between curves. These two branches are related to each other by the fundamental theorem of calculus. They make use of the fundamental notions of convergence of infinite sequences and infinite series to a well-defined limit. It is the "mathematical backbone" for dealing with problems where variables change with time or another reference variable.
  
  Infinitesimal calculus was formulated separately in the late 17th century by Isaac Newton and Gottfried Wilhelm Leibniz. Later work, including codifying the idea of limits, put these developments on a more solid conceptual footing. Today, calculus is widely used in science, engineering, biology, and even has applications in social science and other branches of math. (Full article...)
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  An ecosystem (or ecological system) is a system that environments and their organisms form through their interaction. The biotic and abiotic components are linked together through nutrient cycles and energy flows.
  
  Ecosystems are controlled by external and internal factors. External factors such as climate, parent material which forms the soil and topography, control the overall structure of an ecosystem but are not themselves influenced by the ecosystem. Internal factors are controlled, for example, by decomposition, root competition, shading, disturbance, succession, and the types of species present. While the resource inputs are generally controlled by external processes, the availability of these resources within the ecosystem is controlled by internal factors. Therefore, internal factors not only control ecosystem processes but are also controlled by them.
  
  Ecosystems are dynamic entities—they are subject to periodic disturbances and are always in the process of recovering from some past disturbance. The tendency of an ecosystem to remain close to its equilibrium state, despite that disturbance, is termed its resistance. The capacity of a system to absorb disturbance and reorganize while undergoing change so as to retain essentially the same function, structure, identity, and feedbacks is termed its ecological resilience. Ecosystems can be studied through a variety of approaches—theoretical studies, studies monitoring specific ecosystems over long periods of time, those that look at differences between ecosystems to elucidate how they work and direct manipulative experimentation. Biomes are general classes or categories of ecosystems. However, there is no clear distinction between biomes and ecosystems. Ecosystem classifications are specific kinds of ecological classifications that consider all four elements of the definition of ecosystems: a biotic component, an abiotic complex, the interactions between and within them, and the physical space they occupy. Biotic factors of the ecosystem are living things; such as plants, animals, and bacteria, while abiotic are non-living components; such as water, soil and atmosphere. (Full article...)
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  Wildfire burning in the Kaibab National Forest, Arizona, United States, in 2020. The Mangum Fire burned more than 70,000 acres (280 km²) of forest.

  
  A wildfire, forest fire, or a bushfire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a bushfire (in Australia), desert fire, grass fire, hill fire, peat fire, prairie fire, vegetation fire, or veld fire. Some natural forest ecosystems depend on wildfire. Wildfires are different from controlled or prescribed burning, which are carried out to provide a benefit for people. Modern forest management often engages in prescribed burns to mitigate fire risk and promote natural forest cycles. However, controlled burns can turn into wildfires by mistake.
  
  Wildfires can be classified by cause of ignition, physical properties, combustible material present, and the effect of weather on the fire. Wildfire severity results from a combination of factors such as available fuels, physical setting, and weather. Climatic cycles with wet periods that create substantial fuels, followed by drought and heat, often precede severe wildfires. These cycles have been intensified by climate change.
  
  Wildfires are a common type of disaster in some regions, including Siberia (Russia), California (United States), British Columbia (Canada), and Australia. Areas with Mediterranean climates or in the taiga biome are particularly susceptible. Wildfires can severely impact humans and their settlements. Effects include for example the direct health impacts of smoke and fire, as well as destruction of property (especially in wildland–urban interfaces), and economic losses. There is also the potential for contamination of water and soil. (Full article...)
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  Simplified schematic of an island's fauna – all its animal species, highlighted in boxes

  
  
  Fauna (pl.: faunae or faunas) is all of the animal life present in a particular region or time. The corresponding terms for plants and fungi are flora and funga, respectively. Flora, fauna, funga and other forms of life are collectively referred to as biota. Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess Shale fauna". Paleontologists sometimes refer to a sequence of faunal stages, which is a series of rocks all containing similar fossils. The study of animals of a particular region is called faunistics. (Full article...)

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Selected images

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  Female mallard and ducklings – reproduction is essential for continuing life. (from Nature)
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  A microscopic mite Lorryia formosa (from Nature)
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  Lush green Aravalli Mountain Range in the Desert country – Rajasthan, India. (from Nature)
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  Old growth European Beech forest in Biogradska Gora National Park, Montenegro (from Nature)
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  The Iguazu Falls on the border between Brazil and Argentina (from Nature)
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  An animation showing the movement of the continents from the separation of Pangaea until the present day (from Nature)
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  A tornado in central Oklahoma (from Nature)
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  A selection of diverse plant species (from Nature)
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  A selection of diverse animal species (from Nature)
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  Peñas Blancas, part of the Bosawás Biosphere Reserve. Located northeast of the city of Jinotega in Northeastern Nicaragua (from Nature)
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  Despite their natural beauty, the secluded valleys along the Na Pali Coast in Hawaii are heavily modified by introduced invasive species such as She-oak. (from Nature)
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  The Blue Marble, which is a famous view of the Earth, taken in 1972 by the crew of Apollo 17 (from Nature)
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  The first few hydrogen atom electron orbitals shown as cross-sections with color-coded probability density (from Nature)
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  Blue light is scattered more than other wavelengths by the gases in the atmosphere, giving the Earth a blue halo when seen from space. (from Nature)
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  Lightning (from Nature)
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  A rocky stream in Hawaii (from Nature)
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  Loch Lomond in Scotland forms a relatively isolated ecosystem. The fish community of this lake has remained unchanged over a very long period of time. (from Nature)
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  The Nile river in Cairo, Egypt's capital city (from Nature)
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  Aesthetically pleasing flowers (from Nature)
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  An aerial view of a human ecosystem. Pictured is the city of Chicago. (from Nature)
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  A timelapse composite panorama of different natural phenomena and environments around Mount Bromo, Indonesia. (from Nature)
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  Plankton inhabit oceans, seas and lakes, and have existed in various forms for at least 2 billion years. (from Nature)
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  Planets of the Solar System (sizes to scale, distances and illumination not to scale) (from Nature)
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  Three types of geological plate tectonic boundaries (from Nature)
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  The Westborough Reservoir (Mill Pond) in Westborough, Massachusetts (from Nature)
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  NGC 4414 is a spiral galaxy in the constellation Coma Berenices about 56,000 light-years in diameter and approximately 60 million light-years from Earth. (from Nature)
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  An area of the Amazon Rainforest shared between Colombia and Brazil. The tropical rainforests of South America contain the largest diversity of species on Earth. (from Nature)
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  A view of the Atlantic Ocean from Leblon, Rio de Janeiro (from Nature)
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  Lake Mapourika, New Zealand (from Nature)

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