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125-492: A large proportion of all life on Earth lives in the ocean. The exact size of this "large proportion" is unknown, since many ocean species are still to be discovered. The ocean is a complex three-dimensional world, covering approximately 71% of the Earth's surface. The habitats studied in marine biology include everything from the tiny layers of surface water in which organisms and abiotic items may be trapped in surface tension between

250-420: A double helix . The two DNA strands are known as polynucleotides since they are composed of simpler units called nucleotides . Each nucleotide is composed of a nitrogen-containing nucleobase —either cytosine (C), guanine (G), adenine (A), or thymine (T)—as well as a sugar called deoxyribose and a phosphate group . The nucleotides are joined to one another in a chain by covalent bonds between

375-420: A living systems theory viewpoint that does not necessarily depend on molecular chemistry. One systemic definition of life is that living things are self-organizing and autopoietic (self-producing). Variations of this include Stuart Kauffman 's definition as an autonomous agent or a multi-agent system capable of reproducing itself, and of completing at least one thermodynamic work cycle . This definition

500-428: A nucleus and other membrane-bound organelles , although they have circular DNA and ribosomes . Bacteria and Archaea are two domains of prokaryotes. The other primary type is the eukaryote cell, which has a distinct nucleus bound by a nuclear membrane and membrane-bound organelles, including mitochondria , chloroplasts , lysosomes , rough and smooth endoplasmic reticulum , and vacuoles . In addition, their DNA

625-841: A backbone, make up a huge portion of all life in the sea. Invertebrate sea life includes Cnidaria such as jellyfish and sea anemones ; Ctenophora ; sea worms including the phyla Platyhelminthes , Nemertea , Annelida , Sipuncula , Echiura , Chaetognatha , and Phoronida ; Mollusca including shellfish , squid , octopus ; Arthropoda including Chelicerata and Crustacea ; Porifera ; Bryozoa ; Echinodermata including starfish ; and Urochordata including sea squirts or tunicates . Over 10,000 species of fungi are known from marine environments. These are parasitic on marine algae or animals, or are saprobes on algae, corals, protozoan cysts, sea grasses, wood and other substrata, and can also be found in sea foam . Spores of many species have special appendages which facilitate attachment to

750-407: A common origin. All life forms require certain core chemical elements for their biochemical functioning. These include carbon , hydrogen , nitrogen , oxygen , phosphorus , and sulfur —the elemental macronutrients for all organisms. Together these make up nucleic acids , proteins and lipids , the bulk of living matter. Five of these six elements comprise the chemical components of DNA,

875-476: A consequence of these microbial activities, the physical-chemical environment on Earth has been changing on a geologic time scale , thereby affecting the path of evolution of subsequent life. For example, the release of molecular oxygen by cyanobacteria as a by-product of photosynthesis induced global changes in the Earth's environment. Because oxygen was toxic to most life on Earth at the time, this posed novel evolutionary challenges, and ultimately resulted in

1000-442: A host cell to make new products. Virus self-assembly within host cells has implications for the study of the origin of life , as it may support the hypothesis that life could have started as self-assembling organic molecules . Some of the earliest theories of life were materialist, holding that all that exists is matter, and that life is merely a complex form or arrangement of matter. Empedocles (430 BC) argued that everything in

1125-545: A huge community of life, including the corals themselves, their symbiotic zooxanthellae , tropical fish and many other organisms. Much attention in marine biology is focused on coral reefs and the El Niño weather phenomenon. In 1998, coral reefs experienced the most severe mass bleaching events on record, when vast expanses of reefs across the world died because sea surface temperatures rose well above normal. Some reefs are recovering, but scientists say that between 50% and 70% of

1250-466: A matter of debate; viruses lack characteristics of life such as cell membranes, metabolism and the ability to grow or respond to their environments. Viruses have been classed into "species" based on their genetics , but many aspects of such a classification remain controversial. The original Linnaean system has been modified many times, for example as follows: The attempt to organise the Eukaryotes into

1375-451: A mean depth of 3.68 km (2.29 mi) and maximum depth of 11 km (6.8 mi). Pelagic life decreases as depth increases. The pelagic zone contrasts with the benthic and demersal zones at the bottom of the sea. The benthic zone is the ecological region at the very bottom, including the sediment surface and some subsurface layers. Marine organisms such as clams and crabs living in this zone are called benthos . Just above

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1500-526: A month in a simulated Martian environment . Beyond the Solar System, the region around another main-sequence star that could support Earth-like life on an Earth-like planet is known as the habitable zone . The inner and outer radii of this zone vary with the luminosity of the star, as does the time interval during which the zone survives. Stars more massive than the Sun have a larger habitable zone, but remain on

1625-448: A resurgence of interest in the work of Russell, Barge and colleagues. Hylomorphism is a theory first expressed by the Greek philosopher Aristotle (322 BC). The application of hylomorphism to biology was important to Aristotle, and biology is extensively covered in his extant writings . In this view, everything in the material universe has both matter and form, and the form of a living thing

1750-801: A set of 355 genes from the last universal common ancestor was tentatively identified. The biosphere is postulated to have developed, from the origin of life onwards, at least some 3.5 billion years ago. The earliest evidence for life on Earth includes biogenic graphite found in 3.7 billion-year-old metasedimentary rocks from Western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone from Western Australia . More recently, in 2015, "remains of biotic life " were found in 4.1 billion-year-old rocks in Western Australia. In 2017, putative fossilised microorganisms (or microfossils ) were announced to have been discovered in hydrothermal vent precipitates in

1875-605: A short period Linnaeus had classified them in the taxon Vermes in Animalia, but later placed them back in Plantae. Herbert Copeland classified the Fungi in his Protoctista , including them with single-celled organisms and thus partially avoiding the problem but acknowledging their special status. The problem was eventually solved by Whittaker , when he gave them their own kingdom in his five-kingdom system . Evolutionary history shows that

2000-462: A small number of kingdoms has been challenged. The Protozoa do not form a clade or natural grouping, and nor do the Chromista (Chromalveolata). The ability to sequence large numbers of complete genomes has allowed biologists to take a metagenomic view of the phylogeny of the whole tree of life . This has led to the realisation that the majority of living things are bacteria, and that all have

2125-530: A state of death , and none is immortal . Many philosophical definitions of living systems have been proposed, such as self-organizing systems. Viruses in particular make definition difficult as they replicate only in host cells. Life exists all over the Earth in air, water, and soil , with many ecosystems forming the biosphere . Some of these are harsh environments occupied only by extremophiles . Life has been studied since ancient times, with theories such as Empedocles 's materialism asserting that it

2250-408: A thousand years. In the late 1740s, Carl Linnaeus introduced his system of binomial nomenclature for the classification of species. Linnaeus attempted to improve the composition and reduce the length of the previously used many-worded names by abolishing unnecessary rhetoric, introducing new descriptive terms and precisely defining their meaning. The fungi were originally treated as plants. For

2375-409: A transition zone between freshwater river environments and saltwater maritime environments. They are subject both to marine influences—such as tides, waves, and the influx of saline water—and to riverine influences—such as flows of fresh water and sediment. The shifting flows of both sea water and fresh water provide high levels of nutrients both in the water column and in sediment, making estuaries among

2500-473: Is a mechanistic explanation for the origin of species by means of natural selection . At the beginning of the 20th century Stéphane Leduc (1853–1939) promoted the idea that biological processes could be understood in terms of physics and chemistry, and that their growth resembled that of inorganic crystals immersed in solutions of sodium silicate. His ideas, set out in his book La biologie synthétique , were widely dismissed during his lifetime, but has incurred

2625-556: Is about 4.54 billion years . Life on Earth has existed for at least 3.5 billion years, with the oldest physical traces of life dating back 3.7 billion years. Estimates from molecular clocks, as summarised in the TimeTree public database, place the origin of life around 4.0 billion years ago. Hypotheses on the origin of life attempt to explain the formation of a universal common ancestor from simple organic molecules via pre-cellular life to protocells and metabolism. In 2016,

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2750-514: Is affected by bathymetry (underwater topography) such as the seafloor, shoreline, or a submarine seamount , as well as by proximity to the boundary between the ocean and the atmosphere at the ocean surface, which brings light for photosynthesis, predation from above, and wind stirring up waves and setting currents in motion. The pelagic zone refers to the open, free waters away from the shore, where marine life can swim freely in any direction unhindered by topographical constraints. The oceanic zone

2875-452: Is also becoming understood that the well-being of marine organisms and other organisms are linked in fundamental ways. The human body of knowledge regarding the relationship between life in the sea and important cycles is rapidly growing, with new discoveries being made nearly every day. These cycles include those of matter (such as the carbon cycle ) and of air (such as Earth's respiration , and movement of energy through ecosystems including

3000-951: Is based on phytoplankton . Phytoplankton manufacture their own food using a process of photosynthesis . Because they need sunlight, they inhabit the upper, sunlit epipelagic zone, which includes the coastal or neritic zone . Biodiversity diminishes markedly in the deeper zones below the epipelagic zone as dissolved oxygen diminishes, water pressure increases, temperatures become colder, food sources become scarce, and light diminishes and finally disappears. Some examples of pelagic invertebrates include krill , copepods , jellyfish , decapod larvae , hyperiid amphipods , rotifers and cladocerans . Thorson's rule states that benthic marine invertebrates at low latitudes tend to produce large numbers of eggs developing to widely dispersing pelagic larvae, whereas at high latitudes such organisms tend to produce fewer and larger lecithotrophic (yolk-feeding) eggs and larger offspring. Pelagic fish live in

3125-479: Is being simulated and explored by scientists and engineers. The definition of life has long been a challenge for scientists and philosophers. This is partially because life is a process, not a substance. This is complicated by a lack of knowledge of the characteristics of living entities, if any, that may have developed outside Earth. Philosophical definitions of life have also been put forward, with similar difficulties on how to distinguish living things from

3250-558: Is capable of forming the various specialised cells that form the adult organism. This specialisation allows multicellular organisms to exploit resources more efficiently than single cells. About 800 million years ago, a minor genetic change in a single molecule, the enzyme GK-PID , may have allowed organisms to go from a single cell organism to one of many cells. Cells have evolved methods to perceive and respond to their microenvironment, thereby enhancing their adaptability. Cell signalling coordinates cellular activities, and hence governs

3375-471: Is closely linked to oceanography , especially biological oceanography , and may be regarded as a sub-field of marine science . It also encompasses many ideas from ecology . Fisheries science and marine conservation can be considered partial offshoots of marine biology (as well as environmental studies ). Marine chemistry , physical oceanography and atmospheric sciences are also closely related to this field. An active research topic in marine biology

3500-422: Is considered the starting point of modern organic chemistry . It is of historical significance because for the first time an organic compound was produced in inorganic reactions. During the 1850s Hermann von Helmholtz , anticipated by Julius Robert von Mayer , demonstrated that no energy is lost in muscle movement, suggesting that there were no "vital forces" necessary to move a muscle. These results led to

3625-421: Is extended by the evolution of novel functions over time. Death is the termination of all vital functions or life processes in an organism or cell. One of the challenges in defining death is in distinguishing it from life. Death would seem to refer to either the moment life ends, or when the state that follows life begins. However, determining when death has occurred is difficult, as cessation of life functions

3750-454: Is extreme and there is no sunlight, but some life still exists. A white flatfish , a shrimp and a jellyfish were seen by the American crew of the bathyscaphe Trieste when it dove to the bottom in 1960. In general, the deep sea is considered to start at the aphotic zone , the point where sunlight loses its power of transference through the water. Many life forms that live at these depths have

3875-425: Is its soul (Greek psyche , Latin anima ). There are three kinds of souls: the vegetative soul of plants, which causes them to grow and decay and nourish themselves, but does not cause motion and sensation; the animal soul , which causes animals to move and feel; and the rational soul , which is the source of consciousness and reasoning, which (Aristotle believed) is found only in man. Each higher soul has all of

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4000-407: Is most likely to exist, within wide bounds of uncertainty. A "Confidence of Life Detection" scale (CoLD) for reporting evidence of life beyond Earth has been proposed. Artificial life is the simulation of any aspect of life, as through computers, robotics , or biochemistry . Synthetic biology is a new area of biotechnology that combines science and biological engineering . The common goal

4125-470: Is not only plausible, but probable or inevitable, possibly resulting in a biophysical cosmology instead of a mere physical cosmology . Other planets and moons in the Solar System and other planetary systems are being examined for evidence of having once supported simple life, and projects such as SETI are trying to detect radio transmissions from possible alien civilisations. Other locations within

4250-428: Is often not simultaneous across organ systems. Such determination, therefore, requires drawing conceptual lines between life and death. This is problematic because there is little consensus over how to define life. The nature of death has for millennia been a central concern of the world's religious traditions and of philosophical inquiry. Many religions maintain faith in either a kind of afterlife or reincarnation for

4375-485: Is organised into chromosomes . All species of large complex organisms are eukaryotes, including animals, plants and fungi, though with a wide diversity of protist microorganisms . The conventional model is that eukaryotes evolved from prokaryotes, with the main organelles of the eukaryotes forming through endosymbiosis between bacteria and the progenitor eukaryotic cell. The molecular mechanisms of cell biology are based on proteins . Most of these are synthesised by

4500-425: Is still much more to learn about the deeper parts of the ocean . In biology, many phyla, families and genera have some species that live in the sea and others that live on land. Marine biology classifies species based on their environment rather than their taxonomy. For this reason, marine biology encompasses not only organisms that live only in a marine environment, but also other organisms whose lives revolve around

4625-412: Is the deep open ocean beyond the continental shelf , which contrasts with the inshore waters near the coast , such as in estuaries or on the continental shelf. Waters in the oceanic zone plunge to the depths of the abyssopelagic and further to the hadopelagic . Coastal waters are generally the relatively shallow epipelagic. Altogether, the pelagic zone occupies 1,330 million km (320 million mi ) with

4750-417: Is the design and construction of new biological functions and systems not found in nature. Synthetic biology includes the broad redefinition and expansion of biotechnology, with the ultimate goals of being able to design and build engineered biological systems that process information, manipulate chemicals, fabricate materials and structures, produce energy, provide food, and maintain and enhance human health and

4875-434: Is to define life as "a self-sustained chemical system capable of undergoing Darwinian evolution ", a definition adopted by a NASA committee attempting to define life for the purposes of exobiology , based on a suggestion by Carl Sagan . This definition, however, has been widely criticised because according to it, a single sexually reproducing individual is not alive as it is incapable of evolving on its own. Others take

5000-793: Is to discover and map the life cycles of various species and where they spend their time. Technologies that aid in this discovery include pop-up satellite archival tags , acoustic tags , and a variety of other data loggers . Marine biologists study how the ocean currents , tides and many other oceanic factors affect ocean life forms, including their growth, distribution and well-being. This has only recently become technically feasible with advances in GPS and newer underwater visual devices. Most ocean life breeds in specific places, nests in others, spends time as juveniles in still others, and in maturity in yet others. Scientists know little about where many species spend different parts of their life cycles especially in

5125-509: Is unlikely or impossible. Organisms that have a wide range of tolerance are more widely distributed than organisms with a narrow range of tolerance. To survive, some microorganisms have evolved to withstand freezing , complete desiccation , starvation , high levels of radiation exposure , and other physical or chemical challenges. These extremophile microorganisms may survive exposure to such conditions for long periods. They excel at exploiting uncommon sources of energy. Characterization of

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5250-426: Is widespread and very diverse under the ocean. Microscopic photosynthetic algae contribute a larger proportion of the world's photosynthetic output than all the terrestrial forests combined. Most of the niche occupied by sub plants on land is actually occupied by macroscopic algae in the ocean, such as Sargassum and kelp , which are commonly known as seaweeds that create kelp forests . Plants that survive in

5375-692: The International Ocean Discovery Program found unicellular life in 120 °C sediment 1.2 km below seafloor in the Nankai Trough subduction zone. According to one researcher, "You can find microbes everywhere—they're extremely adaptable to conditions, and survive wherever they are." The inert components of an ecosystem are the physical and chemical factors necessary for life—energy (sunlight or chemical energy ), water, heat, atmosphere , gravity , nutrients , and ultraviolet solar radiation protection . In most ecosystems,

5500-496: The Nuvvuagittuq Belt of Quebec, Canada that were as old as 4.28 billion years, the oldest record of life on Earth, suggesting "an almost instantaneous emergence of life" after ocean formation 4.4 billion years ago , and not long after the formation of the Earth 4.54 billion years ago. Evolution is the change in heritable characteristics of biological populations over successive generations. It results in

5625-458: The Solar System that may host microbial life include the subsurface of Mars , the upper atmosphere of Venus , and subsurface oceans on some of the moons of the giant planets . Investigation of the tenacity and versatility of life on Earth, as well as an understanding of the molecular systems that some organisms utilise to survive such extremes, is important for the search for extraterrestrial life. For example, lichen could survive for

5750-498: The basket star , swimming cucumber, and the sea pig ; and marine arthropods including the sea spider . Many species at these depths are transparent and eyeless. The name is derived from the realm of Hades , the Greek underworld . This is the deepest part of the ocean at more than 6,000 m (20,000 ft) or 6,500 m (21,300 ft), depending on authority. Such depths are generally located in trenches . The pelagic ecosystem

5875-635: The epipelagic , mesopelagic , bathypelagic , abyssopelagic , and hadopelagic zones. Zones which vary by the amount of light they receive include the photic and aphotic zones . Much of the aphotic zone's energy is supplied by the open ocean in the form of detritus . The deepest recorded oceanic trench measured to date is the Mariana Trench , near the Philippines , in the Pacific Ocean at 10,924 m (35,840 ft). At such depths, water pressure

6000-424: The grimpoteuthis or "dumbo octopus". The giant squid is hunted here by deep-diving sperm whales . The name is derived from Ancient Greek ἄβυσσος  'bottomless' - a holdover from times when the deep ocean was believed to indeed be bottomless. Among the very few creatures living in the cold temperatures, high pressures and complete darkness here are several species of squid; echinoderms including

6125-405: The marine environment are often called seabirds . Examples include albatross , penguins , gannets , and auks . Although they spend most of their lives in the ocean, species such as gulls can often be found thousands of miles inland. There are five main types of marine mammals: cetaceans ( toothed whales and baleen whales ); sirenians such as manatees ; pinnipeds including seals and

6250-455: The microorganisms within the ocean; looking at how they are affected by their environment and how that affects larger marine creatures and their ecosystem. Biological oceanography is similar to marine biology, but it studies ocean life from a different perspective. Biological oceanography takes a bottom up approach in terms of the food web, while marine biology studies the ocean from a top down perspective. Biological oceanography mainly focuses on

6375-586: The saltwater crocodile . Most extant marine reptiles, except for some sea snakes, are oviparous and need to return to land to lay their eggs. Thus most species, excluding sea turtles, spend most of their lives on or near land rather than in the ocean. Despite their marine adaptations, most sea snakes prefer shallow waters nearby land, around islands, especially waters that are somewhat sheltered, as well as near estuaries. Some extinct marine reptiles, such as ichthyosaurs , evolved to be viviparous and had no requirement to return to land. Birds adapted to living in

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6500-480: The soul , or resurrection of the body at a later date. Whether or not viruses should be considered as alive is controversial. They are most often considered as just gene coding replicators rather than forms of life. They have been described as "organisms at the edge of life" because they possess genes , evolve by natural selection, and replicate by making multiple copies of themselves through self-assembly. However, viruses do not metabolise and they require

6625-467: The structure and metabolic diversity of microbial communities in such extreme environments is ongoing. The first classification of organisms was made by the Greek philosopher Aristotle (384–322 BC), who grouped living things as either plants or animals, based mainly on their ability to move. He distinguished animals with blood from animals without blood, which can be compared with the concepts of vertebrates and invertebrates respectively, and divided

6750-439: The walrus ; sea otters ; and the polar bear . All are air-breathing, meaning that while some such as the sperm whale can dive for prolonged periods, all must return to the surface to breathe. The marine ecosystem is large, and thus there are many sub-fields of marine biology. Most involve studying specializations of particular animal groups, such as phycology , invertebrate zoology and ichthyology . Other subfields study

6875-500: The water column of coastal, ocean, and lake waters, but not on or near the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and coral reef fish . Pelagic fish are often migratory forage fish , which feed on plankton , and the larger predatory fish that follow and feed on the forage fish. Examples of migratory forage fish are herring , anchovies , capelin , and menhaden . Examples of larger pelagic fish which prey on

7000-419: The 1740s. Living things are composed of biochemical molecules , formed mainly from a few core chemical elements . All living things contain two types of large molecule, proteins and nucleic acids , the latter usually both DNA and RNA : these carry the information needed by each species, including the instructions to make each type of protein. The proteins, in turn, serve as the machinery which carries out

7125-454: The Sun-like "main sequence" of stellar evolution for a shorter time interval. Small red dwarfs have the opposite problem, with a smaller habitable zone that is subject to higher levels of magnetic activity and the effects of tidal locking from close orbits. Hence, stars in the intermediate mass range such as the Sun may have a greater likelihood for Earth-like life to develop. The location of

7250-403: The abandonment of scientific interest in vitalistic theories, especially after Eduard Buchner 's demonstration that alcoholic fermentation could occur in cell-free extracts of yeast. Nonetheless, belief still exists in pseudoscientific theories such as homoeopathy , which interprets diseases and sickness as caused by disturbances in a hypothetical vital force or life force. The age of Earth

7375-446: The ability to create their own light known as bio-luminescence . Marine life also flourishes around seamounts that rise from the depths, where fish and other sea life congregate to spawn and feed. Hydrothermal vents along the mid-ocean ridge spreading centers act as oases , as do their opposites, cold seeps . Such places support unique biomes and many new microbes and other lifeforms have been discovered at these locations.There

7500-466: The appearance of new species and often the disappearance of old ones. Evolution occurs when evolutionary processes such as natural selection (including sexual selection ) and genetic drift act on genetic variation, resulting in certain characteristics increasing or decreasing in frequency within a population over successive generations. The process of evolution has given rise to biodiversity at every level of biological organisation . Fossils are

7625-417: The area that extends from the shoreline to the edge of the continental shelf . Most marine life is found in coastal habitats, even though the shelf area occupies only seven percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of the continental shelf. Alternatively, marine habitats can be divided into pelagic and demersal habitats. Pelagic habitats are found near

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7750-400: The areas that are close to the shore, are constantly being exposed and covered by the ocean's tides . A huge array of life can be found within this zone. Shore habitats span from the upper intertidal zones to the area where land vegetation takes prominence. It can be underwater anywhere from daily to very infrequently. Many species here are scavengers, living off of sea life that is washed up on

7875-450: The attributes of the lower ones. Aristotle believed that while matter can exist without form, form cannot exist without matter, and that therefore the soul cannot exist without the body. This account is consistent with teleological explanations of life , which account for phenomena in terms of purpose or goal-directedness. Thus, the whiteness of the polar bear's coat is explained by its purpose of camouflage. The direction of causality (from

8000-399: The basic functions of multicellular organisms. Signaling between cells can occur through direct cell contact using juxtacrine signalling , or indirectly through the exchange of agents as in the endocrine system . In more complex organisms, coordination of activities can occur through a dedicated nervous system . Though life is confirmed only on Earth, many think that extraterrestrial life

8125-401: The benthic zone is the demersal zone. Demersal fish can be divided into benthic fish , which are denser than water and rest on the bottom, and benthopelagic fish , which swim just above the bottom. Demersal fish are also known as bottom feeders and groundfish . The pelagic zone is subdivided into five vertical regions. From the top down, these are: The illuminated zone at the surface of

8250-436: The biosphere, including soil , hot springs , inside rocks at least 19 km (12 mi) deep underground, the deepest parts of the ocean, and at least 64 km (40 mi) high in the atmosphere. For example, spores of Aspergillus niger have been detected in the mesosphere at an altitude of 48 to 77 km. Under test conditions, life forms have been observed to survive in the vacuum of space. Life forms thrive in

8375-457: The blooded animals into five groups: viviparous quadrupeds ( mammals ), oviparous quadrupeds (reptiles and amphibians ), birds, fishes and whales . The bloodless animals were divided into five groups: cephalopods , crustaceans , insects (which included the spiders, scorpions , and centipedes ), shelled animals (such as most molluscs and echinoderms ), and " zoophytes " (animals that resemble plants). This theory remained dominant for more than

8500-412: The conditions vary during the day and from one season to the next. To live in most ecosystems, then, organisms must be able to survive a range of conditions, called the "range of tolerance". Outside that are the "zones of physiological stress", where the survival and reproduction are possible but not optimal. Beyond these zones are the "zones of intolerance", where survival and reproduction of that organism

8625-422: The deep Mariana Trench , and inside rocks up to 580 m (1,900 ft; 0.36 mi) below the sea floor under 2,590 m (8,500 ft; 1.61 mi) of ocean off the coast of the northwestern United States, and 2,400 m (7,900 ft; 1.5 mi) beneath the seabed off Japan. In 2014, life forms were found living 800 m (2,600 ft; 0.50 mi) below the ice of Antarctica. Expeditions of

8750-418: The development of marine protected areas . This data is important to both scientists and fishermen because they are discovering that, by restricting commercial fishing in one small area, they can have a large impact in maintaining a healthy fish population in a much larger area. The study of marine biology dates to Aristotle (384–322 BC), who made many observations of life in the sea around Lesbos , laying

8875-607: The distinction between plants and animals often breaks down in very small organisms. Other zooplankton include cnidarians , ctenophores , chaetognaths , molluscs , arthropods , urochordates , and annelids such as polychaetes . Many larger animals begin their life as zooplankton before they become large enough to take their familiar forms. Two examples are fish larvae and sea stars (also called starfish ). Microscopic algae and plants provide important habitats for life, sometimes acting as hiding places for larval forms of larger fish and foraging places for invertebrates. Algal life

9000-495: The ecosystem of the ocean with an emphasis on plankton : their diversity (morphology, nutritional sources, motility, and metabolism); their productivity and how that plays a role in the global carbon cycle; and their distribution (predation and life cycle). Biological oceanography also investigates the role of microbes in food webs, and how humans impact the ecosystems in the oceans. Marine habitats can be divided into coastal and open ocean habitats. Coastal habitats are found in

9125-404: The environment. Pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word pelagic is derived from Ancient Greek πέλαγος ( pélagos )  'open sea'. The pelagic zone can be thought of as an imaginary cylinder or water column between the surface of the sea and the bottom. Conditions in

9250-491: The epipelagic zone at night to feed. The name stems from Ancient Greek βαθύς  'deep'. The ocean is pitch black at this depth apart from occasional bioluminescent organisms, such as anglerfish . No plants live here. Most animals survive on detritus known as " marine snow " falling from the zones above or, like the marine hatchetfish , by preying on other inhabitants of this zone. Other examples of this zone's inhabitants are giant squid , smaller squid and

9375-523: The exception being sulfur. The latter is a component of the amino acids cysteine and methionine . The most abundant of these elements in organisms is carbon, which has the desirable attribute of forming multiple, stable covalent bonds . This allows carbon-based (organic) molecules to form the immense variety of chemical arrangements described in organic chemistry . Alternative hypothetical types of biochemistry have been proposed that eliminate one or more of these elements, swap out an element for one not on

9500-512: The first years of their lives in the pelagic zone, moving closer to shore as they reach maturity. Pelagic birds , also called oceanic birds or seabirds , live on open seas and oceans rather than inland or around more restricted waters such as rivers and lakes. Pelagic birds feed on planktonic crustaceans , squid and forage fish . Examples are the Atlantic puffin , macaroni penguins , sooty terns , shearwaters , and Procellariiformes such as

9625-477: The forage fish are billfish , tuna , and oceanic sharks . Hydrophis platurus , the yellow-bellied sea snake, is the only one of the 65 species of marine snakes to spend its entire life in the pelagic zone. It bears live young at sea and is helpless on land. The species sometimes forms aggregations of thousands along slicks in surface waters. The yellow-bellied sea snake is the world's most widely distributed snake species. Many species of sea turtles spend

9750-409: The formation of colonies of identical cells. These cells can form group organisms through cell adhesion . The individual members of a colony are capable of surviving on their own, whereas the members of a true multi-cellular organism have developed specialisations, making them dependent on the remainder of the organism for survival. Such organisms are formed clonally or from a single germ cell that

9875-470: The formation of Earth's major animal and plant species. This interplay between organisms and their environment is an inherent feature of living systems. The biosphere is the global sum of all ecosystems. It can also be termed as the zone of life on Earth, a closed system (apart from solar and cosmic radiation and heat from the interior of the Earth), and largely self-regulating. Organisms exist in every part of

10000-473: The foundation for many future discoveries. In 1768, Samuel Gottlieb Gmelin (1744–1774) published the Historia Fucorum , the first work dedicated to marine algae and the first book on marine biology to use the new binomial nomenclature of Linnaeus . It included elaborate illustrations of seaweed and marine algae on folded leaves. The British naturalist Edward Forbes (1815–1854) is generally regarded as

10125-509: The founder of the science of marine biology. The pace of oceanographic and marine biology studies quickly accelerated during the course of the 19th century. The observations made in the first studies of marine biology fueled the Age of Discovery and exploration that followed. During this time, a vast amount of knowledge was gained about the life that exists in the oceans of the world. Many voyages contributed significantly to this pool of knowledge. Among

10250-406: The fungi are more closely related to animals than to plants. As advances in microscopy enabled detailed study of cells and microorganisms, new groups of life were revealed, and the fields of cell biology and microbiology were created. These new organisms were originally described separately in protozoa as animals and protophyta/thallophyta as plants, but were united by Ernst Haeckel in

10375-480: The future to the past) is in contradiction with the scientific evidence for natural selection, which explains the consequence in terms of a prior cause. Biological features are explained not by looking at future optimal results, but by looking at the past evolutionary history of a species, which led to the natural selection of the features in question. Spontaneous generation was the belief that living organisms can form without descent from similar organisms. Typically,

10500-426: The given environment. This implies all or most of the following traits: From a physics perspective, an organism is a thermodynamic system with an organised molecular structure that can reproduce itself and evolve as survival dictates. Thermodynamically, life has been described as an open system which makes use of gradients in its surroundings to create imperfect copies of itself. Another way of putting this

10625-422: The home to many exotic biological materials that may inspire biomimetic materials . Through constant monitoring of the ocean, there have been discoveries of marine life which could be used to create remedies for certain diseases such as cancer and leukemia. In addition, Ziconotide, an approved drug used to treat pain, was created from a snail which resides in the ocean. Marine biology is a branch of biology . It

10750-434: The idea was that certain forms such as fleas could arise from inanimate matter such as dust or the supposed seasonal generation of mice and insects from mud or garbage. The theory of spontaneous generation was proposed by Aristotle , who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it was considered the best explanation for two millennia. It

10875-410: The infant and juvenile years. For example, it is still largely unknown where juvenile sea turtles and some sharks in the first year of their life travel. Recent advances in underwater tracking devices are illuminating what we know about marine organisms that live at great ocean depths. The information that pop-up satellite archival tags gives aids in fishing closures for certain times of the year and

11000-496: The information to be preserved during reproduction and cell division. Within cells, DNA is organised into long structures called chromosomes . During cell division these chromosomes are duplicated in the process of DNA replication , providing each cell its own complete set of chromosomes. Eukaryotes store most of their DNA inside the cell nucleus . Cells are the basic unit of structure in every living thing, and all cells arise from pre-existing cells by division . Cell theory

11125-632: The kingdom Protista ; later, the prokaryotes were split off in the kingdom Monera , which would eventually be divided into two separate groups, the Bacteria and the Archaea . This led to the six-kingdom system and eventually to the current three-domain system , which is based on evolutionary relationships. However, the classification of eukaryotes, especially of protists, is still controversial. As microbiology developed, viruses, which are non-cellular, were discovered. Whether these are considered alive has been

11250-563: The list, or change required chiralities or other chemical properties. Deoxyribonucleic acid or DNA is a molecule that carries most of the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms and many viruses. DNA and RNA are nucleic acids ; alongside proteins and complex carbohydrates , they are one of the three major types of macromolecule that are essential for all known forms of life. Most DNA molecules consist of two biopolymer strands coiled around each other to form

11375-423: The many chemical processes of life. The cell is the structural and functional unit of life. Smaller organisms, including prokaryotes (bacteria and archaea ), consist of small single cells. Larger organisms , mainly eukaryotes , can consist of single cells or may be multicellular with more complex structure. Life is only known to exist on Earth but extraterrestrial life is thought probable . Artificial life

11500-508: The middle of the 19th century. It appealed to philosophers such as Henri Bergson , Friedrich Nietzsche , and Wilhelm Dilthey , anatomists like Xavier Bichat , and chemists like Justus von Liebig . Vitalism included the idea that there was a fundamental difference between organic and inorganic material, and the belief that organic material can only be derived from living things. This was disproved in 1828, when Friedrich Wöhler prepared urea from inorganic materials. This Wöhler synthesis

11625-515: The most productive natural habitats in the world. Reefs comprise some of the densest and most diverse habitats in the world. The best-known types of reefs are tropical coral reefs which exist in most tropical waters; however, reefs can also exist in cold water. Reefs are built up by corals and other calcium -depositing animals, usually on top of a rocky outcrop on the ocean floor. Reefs can also grow on other surfaces, which has made it possible to create artificial reefs . Coral reefs also support

11750-421: The most significant were the voyages of HMS  Beagle where Charles Darwin came up with his theories of evolution and on the formation of coral reefs . Another important expedition was undertaken by HMS Challenger , where findings were made of unexpectedly high species diversity among fauna stimulating much theorizing by population ecologists on how such varieties of life could be maintained in what

11875-448: The non-living. Legal definitions of life have been debated, though these generally focus on the decision to declare a human dead, and the legal ramifications of this decision. At least 123 definitions of life have been compiled. Since there is no consensus for a definition of life, most current definitions in biology are descriptive. Life is considered a characteristic of something that preserves, furthers or reinforces its existence in

12000-402: The ocean and atmosphere, to the depths of the oceanic trenches , sometimes 10,000 meters or more beneath the surface of the ocean. Specific habitats include estuaries , coral reefs , kelp forests , seagrass meadows , the surrounds of seamounts and thermal vents , tidepools , muddy, sandy and rocky bottoms, and the open ocean ( pelagic ) zone, where solid objects are rare and the surface of

12125-440: The ocean). Large areas beneath the ocean surface still remain effectively unexplored. Marine biology can be contrasted with biological oceanography . Marine life is a field of study both in marine biology and in biological oceanography . Biological oceanography is the study of how organisms affect and are affected by the physics , chemistry , and geology of the oceanographic system . Biological oceanography mostly focuses on

12250-560: The oldest from the Archaean Eon, up to 3.4 billion years old. Extinction is the process by which a species dies out. The moment of extinction is the death of the last individual of that species. Because a species' potential range may be very large, determining this moment is difficult, and is usually done retrospectively after a period of apparent absence. Species become extinct when they are no longer able to survive in changing habitat or against superior competition. Over 99% of all

12375-606: The parent cell divides into two or more daughter cells. For prokaryotes, cell division occurs through a process of fission in which the DNA is replicated, then the two copies are attached to parts of the cell membrane. In eukaryotes , a more complex process of mitosis is followed. However, the result is the same; the resulting cell copies are identical to each other and to the original cell (except for mutations ), and both are capable of further division following an interphase period. Multicellular organisms may have first evolved through

12500-531: The physical effects of continual immersion in sea water and the ocean in general, adaptation to a salty environment, and the effects of changing various oceanic properties on marine life. A subfield of marine biology studies the relationships between oceans and ocean life, and global warming and environmental issues (such as carbon dioxide displacement). Recent marine biotechnology has focused largely on marine biomolecules , especially proteins , that may have uses in medicine or engineering. Marine environments are

12625-466: The preserved remains or traces of organisms from the remote past. The totality of fossils, both discovered and undiscovered, and their placement in layers ( strata ) of sedimentary rock is known as the fossil record . A preserved specimen is called a fossil if it is older than the arbitrary date of 10,000 years ago. Hence, fossils range in age from the youngest at the start of the Holocene Epoch to

12750-456: The ribosomes through an enzyme-catalyzed process called protein biosynthesis . A sequence of amino acids is assembled and joined based upon gene expression of the cell's nucleic acid. In eukaryotic cells, these proteins may then be transported and processed through the Golgi apparatus in preparation for dispatch to their destination. Cells reproduce through a process of cell division in which

12875-807: The role of viruses in marine ecosystems is barely being explored even in the beginning of the 21st century. The role of phytoplankton is better understood due to their critical position as the most numerous primary producers on Earth. Phytoplankton are categorized into cyanobacteria (also called blue-green algae/bacteria), various types of algae (red, green, brown, and yellow-green), diatoms , dinoflagellates , euglenoids , coccolithophorids , cryptomonads , chrysophytes , chlorophytes , prasinophytes , and silicoflagellates . Zooplankton tend to be somewhat larger, and not all are microscopic. Many Protozoa are zooplankton, including dinoflagellates, zooflagellates , foraminiferans , and radiolarians . Some of these (such as dinoflagellates) are also phytoplankton;

13000-408: The sea are often found in shallow waters, such as the seagrasses (examples of which are eelgrass, Zostera , and turtle grass, Thalassia ). These plants have adapted to the high salinity of the ocean environment. The intertidal zone is also a good place to find plant life in the sea, where mangroves or cordgrass or beach grass might grow. As on land, invertebrates , or animals that lack

13125-531: The sea with sufficient light for photosynthesis. Nearly all primary production in the ocean occurs here, and marine life is concentrated in this zone, including plankton , floating seaweed , jellyfish , tuna , many sharks and dolphins . The most abundant organisms thriving into the mesopelagic zone are heterotrophic bacteria. Animals living in this zone include swordfish , squid , wolffish and some species of cuttlefish . Many organisms living here are bioluminescent . Some mesopelagic creatures rise to

13250-406: The sea. As inhabitants of the largest environment on Earth, microbial marine systems drive changes in every global system. Microbes are responsible for virtually all photosynthesis that occurs in the ocean, as well as the cycling of carbon , nitrogen , phosphorus and other nutrients and trace elements. Microscopic life undersea is incredibly diverse and still poorly understood. For example,

13375-423: The shore. Many land animals also make much use of the shore and intertidal habitats. A subgroup of organisms in this habitat bores and grinds exposed rock through the process of bioerosion . Estuaries are also near shore and influenced by the tides . An estuary is a partially enclosed coastal body of water with one or more rivers or streams flowing into it and with a free connection to the open sea. Estuaries form

13500-435: The soul, like everything else, was composed of fiery atoms. He elaborated on fire because of the apparent connection between life and heat, and because fire moves. Plato , in contrast, held that the world was organised by permanent forms , reflected imperfectly in matter; forms provided direction or intelligence, explaining the regularities observed in the world. The mechanistic materialism that originated in ancient Greece

13625-493: The species that have ever lived are now extinct. Mass extinctions may have accelerated evolution by providing opportunities for new groups of organisms to diversify. The diversity of life on Earth is a result of the dynamic interplay between genetic opportunity , metabolic capability, environmental challenges, and symbiosis . For most of its existence, Earth's habitable environment has been dominated by microorganisms and subjected to their metabolism and evolution. As

13750-484: The star within a galaxy may also affect the likelihood of life forming. Stars in regions with a greater abundance of heavier elements that can form planets, in combination with a low rate of potentially habitat -damaging supernova events, are predicted to have a higher probability of hosting planets with complex life. The variables of the Drake equation are used to discuss the conditions in planetary systems where civilisation

13875-419: The substratum. A very diverse range of unusual secondary metabolites is produced by marine fungi. A reported 33,400 species of fish , including bony and cartilaginous fish , had been described by 2016, more than all other vertebrates combined. About 60% of fish species live in saltwater. Reptiles which inhabit or frequent the sea include sea turtles , sea snakes , terrapins , the marine iguana , and

14000-408: The sugar of one nucleotide and the phosphate of the next, resulting in an alternating sugar-phosphate backbone . According to base pairing rules (A with T, and C with G), hydrogen bonds bind the nitrogenous bases of the two separate polynucleotide strands to make double-stranded DNA. This has the key property that each strand contains all the information needed to recreate the other strand, enabling

14125-426: The surface or in the open water column , away from the bottom of the ocean and affected by ocean currents , while demersal habitats are near or on the bottom. Marine habitats can be modified by their inhabitants. Some marine organisms, like corals, kelp and sea grasses, are ecosystem engineers which reshape the marine environment to the point where they create further habitat for other organisms. Intertidal zones ,

14250-413: The universe is made up of a combination of four eternal "elements" or "roots of all": earth, water, air, and fire. All change is explained by the arrangement and rearrangement of these four elements. The various forms of life are caused by an appropriate mixture of elements. Democritus (460 BC) was an atomist ; he thought that the essential characteristic of life was having a soul ( psyche ), and that

14375-423: The water column change with depth: pressure increases; temperature and light decrease; salinity, oxygen, micronutrients (such as iron, magnesium and calcium) all change. In a manner analogous to stratification in the Earth's atmosphere , the water column can be divided vertically into up to five different layers (illustrated in the diagram), with the number of layers depending on the depth of the water. Marine life

14500-434: The water is the only visible boundary. The organisms studied range from microscopic phytoplankton and zooplankton to huge cetaceans (whales) 25–32 meters (82–105 feet) in length. Marine ecology is the study of how marine organisms interact with each other and the environment. Marine life is a vast resource, providing food, medicine, and raw materials, in addition to helping to support recreation and tourism all over

14625-415: The world's coral reefs are now endangered and predict that global warming could exacerbate this trend. The open ocean is relatively unproductive because of a lack of nutrients, yet because it is so vast, in total it produces the most primary productivity. The open ocean is separated into different zones, and the different zones each have different ecologies. Zones which vary according to their depth include

14750-719: The world, Station biologique de Roscoff , was established in Concarneau, France founded by the College of France in 1859. In the United States, the Scripps Institution of Oceanography dates back to 1903, while the prominent Woods Hole Oceanographic Institute was founded in 1930. The development of technology such as sound navigation and ranging , scuba diving gear, submersibles and remotely operated vehicles allowed marine biologists to discover and explore life in deep oceans that

14875-428: The world. At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms contribute significantly to the oxygen cycle , and are involved in the regulation of the Earth's climate . Shorelines are in part shaped and protected by marine life, and some marine organisms even help create new land. Many species are economically important to humans, including both finfish and shellfish. It

15000-535: Was composed of four eternal elements , and Aristotle 's hylomorphism asserting that living things have souls and embody both form and matter. Life originated at least 3.5 billion years ago, resulting in a universal common ancestor . This evolved into all the species that exist now, by way of many extinct species, some of which have left traces as fossils . Attempts to classify living things, too, began with Aristotle . Modern classification began with Carl Linnaeus 's system of binomial nomenclature in

15125-414: Was decisively dispelled by the experiments of Louis Pasteur in 1859, who expanded upon the investigations of predecessors such as Francesco Redi . Disproof of the traditional ideas of spontaneous generation is no longer controversial among biologists. Vitalism is the belief that there is a non-material life-principle. This originated with Georg Ernst Stahl (17th century), and remained popular until

15250-495: Was formulated by Henri Dutrochet , Theodor Schwann , Rudolf Virchow and others during the early nineteenth century, and subsequently became widely accepted. The activity of an organism depends on the total activity of its cells, with energy flow occurring within and between them. Cells contain hereditary information that is carried forward as a genetic code during cell division. There are two primary types of cells, reflecting their evolutionary origins. Prokaryote cells lack

15375-565: Was once thought to not exist. Public interest in the subject continued to develop in the post-war years with the publication of Rachel Carson 's sea trilogy (1941–1955). Life Life on Earth: Life is a quality that distinguishes matter that has biological processes , such as signaling and self-sustaining processes, from matter that does not. It is defined descriptively by the capacity for homeostasis , organisation , metabolism , growth , adaptation , response to stimuli , and reproduction . All life over time eventually reaches

15500-482: Was revived and revised by the French philosopher René Descartes (1596–1650), who held that animals and humans were assemblages of parts that together functioned as a machine. This idea was developed further by Julien Offray de La Mettrie (1709–1750) in his book L'Homme Machine . In the 19th century the advances in cell theory in biological science encouraged this view. The evolutionary theory of Charles Darwin (1859)

15625-464: Was thought to be such a hostile environment. This era was important for the history of marine biology but naturalists were still limited in their studies because they lacked technology that would allow them to adequately examine species that lived in deep parts of the oceans. The creation of marine laboratories was important because it allowed marine biologists to conduct research and process their specimens from expeditions. The oldest marine laboratory in

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