76 Their existence was discovered through electron microscopy and epifluorescence microscopy of ecological water samples, and later through metagenomic sampling of uncultured viral samples. 76 77 The tailed bacteriophages appear to dominate marine ecosystems in number and diversity of organisms. 76 However, viruses belonging to families Corticoviridae, 78 Inoviridae 79 and Microviridae 80 are also known to infect diverse marine bacteria. Metagenomic evidence suggests that microviruses (icosahedral ssdna phages) are particularly prevalent in marine habitats. 80 Bacteriophages, viruses that are parasitic on bacteria, were first discovered in the early twentieth century. Scientists today consider that their importance in ecosystems, particularly marine ecosystems, has been underestimated, leading to these infectious agents being poorly investigated and their numbers and species biodiversity being greatly under reported. 81 Microscopic organisms live in every part of the biosphere.
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69 As inhabitants of the largest environment on Earth, microbial writing marine systems drive changes in every global system. Microbes are responsible for virtually all the photosynthesis that occurs in the ocean, as well as the cycling of carbon, nitrogen, phosphorus and other nutrients and trace elements. 70 Microscopic life undersea is incredibly diverse and still poorly understood. For example, the role of viruses in marine ecosystems is barely being explored even in the beginning of the 21st century. 71 A teaspoon of seawater contains about one million viruses. 72 Most of these are bacteriophages, which are harmless to plants and animals, and are in fact essential to the regulation of saltwater and freshwater ecosystems. 73 They infect and destroy bacteria in aquatic microbial communities, and are the most important mechanism of recycling carbon in the marine environment. The organic molecules released from the dead bacterial cells stimulate fresh bacterial and algal growth. 74 Viral activity may also contribute to the biological pump, the process whereby carbon is sequestered in the deep ocean. 75 Marine bacteriophages are viruses that live as obligate parasitic agents in marine bacteria such as cyanobacteria.
A microorganism (or microbe) is a microscopic living organism, book which may be single-celled 65 or multicellular. Microorganisms are very diverse and include all bacteria, archaea and most protozoa. This group also contains some species of fungi, algae, and certain microscopic animals, such as rotifers. Many macroscopic animals and plants have microscopic juvenile stages. Some microbiologists also classify viruses (and viroids ) as microorganisms, but others consider these as nonliving. 66, scientists reported identifying a set of 355 genes from the last universal common ancestor (luca) of all life, including microorganisms, living on Earth. 68 Microorganisms are crucial to nutrient recycling in ecosystems as they act as decomposers. A small proportion of microorganisms are pathogenic, causing disease and even death in plants and animals.
54 About 500 million years ago, plants and fungi started colonising the land. Evidence for the appearance of the first land plants occurs in the Ordovician, around 450 million years ago, in the form of fossil spores. 55 Land plants began to diversify in the late silurian, from around 430 million years ago. 56 The colonisation of the land by plants was soon followed by arthropods and other animals. 57 Insects were particularly successful and even today make up the majority of animal species. 58 Amphibians first appeared around 364 million years ago, followed by early amniotes and birds around 155 million years ago (both from " reptile "-like lineages mammals around 129 million years ago, homininae around 10 million years ago and modern humans around 250,000 years ago. However, despite the evolution of these large animals, smaller organisms similar to the types that evolved early in this process continue to be highly successful and dominate the earth, with the majority of both biomass and species being prokaryotes. 62 Estimates on the number of Earth's current species range from 10 million to 14 million, 63 of which about.2 million have been documented and over 86 percent have not yet been described. 64 Marine microorganisms edit microbial mats main article: Marine microorganism see also: evolution of cells Microorganisms constitute more than 90 of the marine biomass.
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42 Prokaryotes inhabited the earth from approximately 34 billion help years ago. 43 44 no obvious changes in morphology or cellular organisation occurred in these organisms over the next few billion years. 45 The eukaryotic cells emerged between.62.7 billion years ago. The next major change in cell structure came when bacteria were engulfed by eukaryotic cells, in a cooperative association called endosymbiosis. 46 47 The engulfed bacteria and the host cell then underwent coevolution, with the bacteria evolving into either mitochondria or hydrogenosomes.
48 Another engulfment of cyanobacterial -like organisms led to the formation of chloroplasts in algae and plants. 49 Phylogenetic and symbiogenetic tree of living organisms, showing the origins of eukaryotes and prokaryotes The history of life was that of the unicellular eukaryotes, prokaryotes and archaea until about 610 million years ago when multicellular organisms began to appear in the oceans in the. 43 50 The evolution of multicellularity occurred in multiple independent events, in organisms as diverse as sponges, brown algae, cyanobacteria, slime moulds and myxobacteria. 51 In January 2016, scientists reported that, about 800 million years ago, a minor genetic change in a single molecule called gk-pid may have allowed organisms to go from a single cell organism to one of many cells. 52 soon after book the emergence of these first multicellular organisms, a remarkable amount of biological diversity appeared over approximately 10 million years, in an event called the cambrian explosion. Here, the majority of types of modern animals appeared in the fossil record, as well as unique lineages that subsequently became extinct. 53 Various triggers for the cambrian explosion have been proposed, including the accumulation of oxygen in the atmosphere from photosynthesis.
31 The beginning of life may have included self-replicating molecules such as rna 32 and the assembly of simple cells. 33 Current species are a stage in the process of evolution, with their diversity the product of a long series of speciation and extinction events. 34 The common descent of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of completely unique organisms, but organisms that share morphological similarities. Third, vestigial traits with no clear purpose resemble functional ancestral traits and finally, that organisms can be classified using these similarities into a hierarchy of nested groups—similar to a family tree. 35 However, modern research has suggested that, due to horizontal gene transfer, this "tree of life" may be more complicated than a simple branching tree since some genes have spread independently between distantly related species.
36 37 Past species have also left records of their evolutionary history. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record. 38 by comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. However, this approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. Further, as prokaryotes such as bacteria and archaea share a limited set of common morphologies, their fossils do not provide information on their ancestry. More recently, evidence for common descent has come from the study of biochemical similarities between organisms. For example, all living cells use the same basic set of nucleotides and amino acids. 40 The development of molecular genetics has revealed the record of evolution left in organisms' genomes: dating when species diverged through the molecular clock produced by mutations. 41 For example, these dna sequence comparisons have revealed that humans and chimpanzees share 98 of their genomes and analysing the few areas where they differ helps shed light on when the common ancestor of these species existed.
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14 sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir. 15 Shifts in the oceanic temperature distribution can cause significant weather revelation shifts, such as the El niño-southern Oscillation. 16 evolution edit life timeline view discuss edit -4500 — -4000 — -3500 — -3000 — -2500 — -2000 — -1500 — -1000 — -500 — 0 — Axis scale : million years Also see: Human timeline and Nature timeline further information: evolutionary history of life and Timeline of evolutionary history of life The earth. The earliest undisputed evidence of life on Earth dates from at least.5 billion years ago, 20 21 during the eoarchean Era after a geological crust started to solidify following the earlier molten Hadean Eon. Microbial mat fossils have been found.48 billion-year-old sandstone in Western Australia. Other early physical evidence of a biogenic substance is graphite.7 billion-year-old metasedimentary rocks discovered in Western Greenland 25 as well as "remains of biotic life " found.1 billion-year-old rocks in Western Australia. 26 27 According to one of the researchers, "If life arose relatively quickly on Earth then it could be common in the universe." 26 All organisms on Earth are descended from a common ancestor or ancestral gene pool. 28 29 Highly energetic chemistry is thought to have produced a self-replicating molecule around 4 billion years ago, and half a billion years later the last common ancestor of all life existed. 30 The current scientific consensus is that the complex biochemistry that makes up life came from simpler chemical reactions.
The deepest underwater location is Challenger deep of the mariana Trench in the pacific Ocean with a depth of 10,911.4. Note 1 7 The mass of the oceans is approximately.351018 metric tons, or about 1/4400 of Earth's total mass. The oceans cover an area.618108 km2 with a mean depth of m, resulting essay in an estimated volume.332109 km3. 8 If all of Earth's crustal surface was at the same elevation as a smooth sphere, the depth of the resulting world ocean would.7.8 km. 9 10 About.5 of the water is saline; the remaining.5 is fresh water. Most fresh water, about.7, is present as ice in ice caps and glaciers. 11 The average salinity of Earth's oceans is about 35 grams of salt per kilogram of sea water (3.5 salt). 12 Most of this salt was released from volcanic activity or extracted from cool igneous rocks. 13 The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms.
breathing tubes (see insect and mollusc siphons ) and gills ( Carcinus ). However, as invertebrate life evolved in an aquatic habitat most have little or no specialisation for respiration in water. Altogether there are 230,000 documented marine species, including over 16,000 species of fish, and it has been estimated that nearly two million marine species are yet to be documented. 2 Marine species range in size from the microscopic, including plankton and phytoplankton which can be as small.02 micrometres, to huge cetaceans (whales, dolphins and porpoises) which in the case of the blue whale reach up to 33 metres (109 feet) in length. 3 4 Contents Elevation histogram of Earth's surface main article: Hydrosphere There is no life without water, which has been characterised as the "solvent of life". 5 The nobel prize winner Albert szent-györgyi referred to water as the mater und matrix, the mother and womb of life. 6 The abundance of water on earth's surface is a unique feature that distinguishes earth from other planets in the solar System. Earth's hydrosphere consists chiefly of the oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters down to a depth of 2,000.
Oceans provide about 99 percent of the living space on the planet. 1, the earliest vertebrates appeared in the form night of fish, which live exclusively in water. Some of these evolved into amphibians which spend portions of their lives in water and portions on land. Other fish evolved into land mammals and subsequently returned to the ocean as seals, dolphins or whales. Plant forms such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton, and particularly phytoplankton, are key primary producers forming the general foundation of the ocean food chain. Marine vertebrates must obtain oxygen to survive, and they do so in various ways. Fish have gills instead of lungs, although some species of fish, such as the lungfish, have both.
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Killer whales ( orca ) are marine apex predators. They hunt practically anything, including tuna, smaller sharks and seals. However, the oceans are alive best with less obvious, but equally important forms of marine life, such as bacteria. Marine life, or sea life or ocean life, is the plants, animals and other organisms that live in the salt water of the sea or ocean, or the brackish water of coastal estuaries. At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms produce much of the oxygen we breathe. Shorelines are in part shaped and protected by marine life, and some marine organisms even help create new land. Most life forms evolved initially in marine habitats.