of each other In the older literature, the term Phanerozoic is generally used as a label for the time period of interest to paleontologists, but that use of the term seems to be falling into disuse in more modern literature Eras of the Phanerozoic edit The Phanerozoic is divided into three eras the Paleozoic, Mesozoic, and Cenozoic, and consisting of periods the Cambrian, the Ordovician, the Silurian, the Devonian, the Carboniferous, the Permian, the Triassic, the Jurassic, the Cretaceous, the Paleogene, the Neogene, and the Quaternary The Paleozoic features the rise of fish, amphibians and reptiles The Mesozoic is ruled by the reptiles, and features the evolution of mammals, birds and more famously, dinosaurs The Cenozoic is the time of the mammals, and more recently, humans Paleozoic era edit Main article Paleozoic The Paleozoic is a time in earth's history when complex life forms evolve, take their first breath of oxygen on dry land, and when the forerunners of all life on earth begin to diversify There are six periods in the Paleozoic era the Cambrian, the Ordovician, the Silurian, the Devonian, the Carboniferous and the Permian Cambrian edit Main article Cambrian Trilobites The Cambrian spans from million years to million years ago and is the first period of the Paleozoic and of the Phanerozoic eon The Cambrian sparks a boom in evolution in an event known as the Cambrian Explosion in which the largest number of creatures evolve in the history of Earth during one period Plants like algae evolve, the fauna is dominated by armored arthropods, like trilobites Almost all marine phyla evolved in this period During this time, the super continent Pannotia begins to break up, most of which becomes the super continent Gondwana Ordovician edit Main article Ordovician Cephalaspis a jaw less fish The Ordovician spans from million years to million years ago The Ordovician is a time in Earth's history in which many species still prevalent today evolved, such as primitive fish, cephalopods, and coral The most common forms of life, however, were trilobites, snails and shellfish More importantly, the first arthropods went ashore to colonize the empty continent of Gondwana By the end of the period, Gondwana was at the south pole, early North America had collided with Europe, closing the Atlantic Ocean Glaciation of Africa resulted in a major drop in sea level, killing off all life that staked a claim along coastal Gondwana Glaciation caused a snowball Earth, leading to the Ordovician Silurian extinction, when % of marine invertebrates and % of families went extinct This is considered the first mass extinction and the second deadliest extinction in the history of Earth Silurian edit Main article Silurian The Silurian spans from million years to million years ago The Silurian saw the healing of the earth that recovered from the Snowball Earth This period saw the mass evolution of fish, as jaw less fish became more numerous, jawed fish evolved, and the first freshwater fish evolved, though arthropods, such as sea scorpions, were still apex predators Fully terrestrial life evolved, which included early arachnids, fungi, and centipedes Also, the evolution of vascular plants Cooksonia allowed plants to gain a foothold on

land These early terrestrial plants are the forerunners of all plant life on land During this time, there are four continents Gondwana Africa, South America, Australia, Antarctica, India , Laurentia North America with parts of Europe , Baltica the rest of Europe , and Siberia Northern Asia The recent rise in sea levels provided many new species to thrive in water Devonian edit Main article Devonian Eogyrinus an amphibian of the Carboniferous The Devonian spans from million years to million years ago Also known as The Age of the Fish , the Devonian features a huge diversification in fish, including armored fish like Dunkleosteus and lobe finned fish which eventually evolved into the first tetrapods On land, plant groups diversified incredibly in an event known as the Devonian Explosion where the first trees evolved, as well as seeds This event also diversified arthropod life The first amphibians also evolved, and the fish were now at the top of the food chain Near the end of the Devonian, % of all species went extinct in an event known as the Late Devonian extinction, which is the second mass extinction known to have happened Carboniferous edit Main article Carboniferous Dimetrodon The Carboniferous spans from million to million years ago During this time, average global temperatures were exceedingly high the early Carboniferous averaged at about degrees Celsius but cooled down to degrees during the Middle Carboniferous Tropical swamps dominated the earth, and the large amounts of trees created much of the carbon for the coal that is used today hence the name Carbon iferous Perhaps the most important evolutionary development of the time was the evolution of amniotic eggs, which allowed amphibians to head farther inland and remain the dominant vertebrae throughout the period Also, the first reptiles and synapsids evolved in the swamps Throughout the Carboniferous, there was a cooling pattern, which eventually led to the glaciation of Gondwana as much of it was situated around the south pole, in an event known as the Permo Carboniferous glaciation or the Carboniferous Rainforest Collapse Permian edit Main article Permian The Permian spans from million to million years ago and was the last period of the Paleozoic At the beginning, all continents clamped together to form the super continent Pangaea, surrounded by one ocean called Panthalassa The earth was very dry during this time, with harsh seasons, as the climate of the interior of Pangaea wasn't regulated by large bodies of water Reptiles and synapsids flourished in the new dry climate Creatures such as Dimetrodon and Edaphosaurus ruled the new continent The first conifers evolved, then dominated the terrestrial landscape Nearing the end of the period, Scutosaurus and gorgonopsids filled the empty desert Eventually, they disappeared, along with % of all life on earth in an event simply known as the Great Dying , the world's third mass extinction event Mesozoic era edit Main article Mesozoic Also known as the Age of the dinosaurs , the Mesozoic features the rise of reptiles on their million year conquest to rule the earth from the seas, the land, and even in the air There are periods in the Mesozoic the Triassic, the Jurassic, and the Cretaceous Triassic edit Main article Triassic The Triassic ranges from million to million years ago The Triassic is a desolate transitional state in Earth's history between the Permian Extinction and the lush Jurassic Period It has three major epochs the Early Triassic, the Middle Triassic and the Late Triassic The Early Triassic lasted between million to million years ago and was dominated by deserts as Pangaea had not yet broken up, thus the interior was nothing but arid The Earth had just witnessed a massive die off in which % of all life went extinct The most common life on earth were Lystrosaurus, labyrinthodonts, and Euparkeria along with many other creatures that managed to survive the Great Dying Temnospondyli evolved during this time and would be the dominant predator for much of the Triassic Plateosaurus a prosauropod The Middle Triassic spans from million to million years ago The Middle Triassic featured the beginnings of the breakup of Pangaea, and the beginning of the Tethys Sea The ecosystem had recovered from the devastation of the Great Dying Phytoplankton, coral, and crustaceans all had recovered, and the reptiles began to get bigger and bigger New aquatic reptiles evolved such as ichthyosaurs and nothosaurs Meanwhile, on land, pine forests flourished, bringing along mosquitoes and fruit flies The first ancient crocodilians evolved, which sparked competition with the large amphibians that had since rule the freshwater world The Late Triassic spans from million to million years ago Following the bloom of the Middle Triassic, the Late Triassic featured frequent heat spells, as well as moderate precipitation inches per year The recent warming led to a boom of reptilian evolution on land as the first true dinosaurs evolve, as well as pterosaurs All this climactic change, however, resulted in a large die out known as the Triassic Jurassic extinction event, in which all archosaurs excluding ancient crocodiles , synapsids, and almost all large amphibians went extinct, as well as % of marine life in the fourth mass extinction event of the world The cause is debatable Jurassic edit Main article Jurassic Rhamphorhynchus The Jurassic ranges from million years to million years ago and features major epochs The Early Jurassic, the Middle Jurassic, and the Late Jurassic The Early Jurassic spans from million years to million years ago The climate was much more humid than the Triassic, and as a result, the world was very tropical In the oceans, plesiosaurs, ichthyosaurs and ammonites filled the waters as the dominant creatures of the seas On land, dinosaurs and other reptiles staked their claim as the dominant race of the land, with species such as Dilophosaurus at the top The first true crocodiles evolved, pushing out the large amphibians to near extinction All in all, reptiles rise to rule the world Meanwhile, the first true mammals evolve, but never exceed the height of a shrew The Middle Jurassic spans from million to million years ago During this epoch, reptiles flourished as huge herds of sauropods, such as Brachiosaurus and Diplodicus, filled the fern prairies of the Middle Jurassic Many other predators rose as well, such as Allosaurus Conifer forests made up a large portion of the forests In the oceans, plesiosaurs were quite common, and ichthyosaurs were flourishing This epoch was the peak of the reptiles Inaccurately portrayed Stegosaurus The Late Jurassic spans from million to million years ago The Late Jurassic featured a massive extinction of sauropods and ichthyosaurs due to the separation of Pangaea into Laurasia and Gondwana in an extinction known as the Jurassic Cretaceous extinction Sea levels rose, destroying fern prairies and creating shallows in its wake Ichthyosaurs went extinct whereas sauropods, as a whole, did not die out in the Jurassic in fact, some species, like Titanosaurus, lived up to the K T extinction The increase in sea levels opened up the Atlantic sea way which would continue to get larger over time The divided world would give opportunity for the diversification of new dinosaurs Cretaceous edit Main article Cretaceous The Cretaceous is the longest period in the Mesozoic, but has only two periods the Early Cretaceous, and the Late Cretaceous Tylosaurus a mosasaur hunting Xiphactinus The Early Cretaceous spans from million to million years ago The Early Cretaceous saw the expansion of seaways, and as a result, the decline and extinction of sauropods except in South America Many coastal shallows were created, and that caused ichthyosaurs to die out Mosasaurs evolved to replace them as head of the seas Some island hopping dinosaurs, like Eustreptospondylus, evolved to cope with the coastal shallows and small islands of ancient Europe Other dinosaurs rose up to fill the empty space that the Jurassic Cretaceous extinction left behind, such as Carcharodontosaurus and Spinosaurus Of the most successful would be the Iguanodon which spread to every continent Seasons came back into effect and the poles got seasonally colder, but dinosaurs still inhabited this area like the Leaellynasaura which inhabited the polar forests year round, and many dinosaurs migrated there during summer like Muttaburrasaurus Since it was too cold for crocodiles, it was the last stronghold for large amphibians, like Koolasuchus Pterosaurs got larger as species like Tapejara and Ornithocheirus evolved More importantly, the first true birds evolved which sparked competition between them and the pterosaurs The Late Cretaceous spans from million to million years ago The Late Cretaceous featured a cooling trend that would continue on in the Cenozoic period Eventually, tropics were restricted to the equator and areas beyond the tropic lines featured extreme seasonal changes in weather Dinosaurs still thrived as new species such as Tyrannosaurus, Ankylosaurus, Triceratops and hadrosaurs dominated the food web Pterosaurs, however, were going into a decline as birds took to the skies The last pterosaur to die off was Quetzalcoatlus Marsupials evolved within the large conifer forests as scavengers In the oceans, Mosasaurs ruled the seas to fill the role of the ichthyosaurs, and huge plesiosaurs, such as Elasmosaurus, evolved Also, the first flowering plants evolved At the end of the Cretaceous, the Deccan Traps and other volcanic eruptions were poisoning the atmosphere As this was continuing, it is thought that a large meteor smashed into earth, creating the Chicxulub Crater in an event known as the K T Extinction, the fifth and most recent mass extinction event, in which % of life on earth went extinct, including all non avian dinosaurs Everything over kilograms went extinct The age of the dinosaurs was officially over Cenozoic era edit Main article Cenozoic The Cenozoic features the rise of mammals on their conquest to rule the land, as the dinosaurs have now left a huge opening as top dog There are three division of the Cenozoic the Paleogene, the Neogene and Quaternary Paleogene edit Main article Paleogene The Paleogene spans from the extinction of the dinosaurs, some million years ago, to the dawn of the Neogene twenty three million years ago It features three epochs the Paleocene, Eocene and Oligocene Basilosaurus a whale, despite the name The Paleocene ranged from million to million years ago The Paleocene is a transitional point between the devastation that is the K T extinction, to the rich jungles environment that is the Early Eocene The Early Paleocene saw the recovery of the earth The continents began to take their modern shape, but all continents and India were separated from each other Afro Eurasia is separated by the Tethys Sea, and the Americas are separated by the strait of Panama, as the isthmus has not yet formed This epoch features a general warming trend, with jungles eventually reaching the poles The oceans were dominated by sharks as the large reptiles that had once ruled went extinct Archaic mammals filled the world such as creodonts and early primates that evolved during the Mesozoic, and as a result, there was nothing over kilograms Mammals are still quite small The Eocene epoch ranged from million years to million years ago In the Early Eocene, life was small and living in cramped jungles, much like the Paleocene There was nothing over the weight of kilograms Among them were early primates, whales and horses along with many other early forms of mammals At the top of the food chains were huge birds, such as Gastornis It is the only time in recorded history that birds ruled the world excluding their ancestors, the dinosaurs The temperature was degrees Celsius with little temperature gradient from pole to pole In the Mid Eocene, the circum Antarctic current between Australia and Antarctica formed which disrupted ocean currents worldwide and as a result caused a global cooling effect, shrinking the jungles This allowed mammals to grow to mammoth


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kristina-king kristina-klevits kristina-soderszk kristine-heller kristin-steen krisztina-ventura krystal-de-boor krystal-steal kylee-karr kylee-nash kylie-brooks kylie-channel kylie-haze kylie-wylde kym-wilde kyoto-sun lachelle-marie lacy-rose lady-amanda-wyldefyre lady-stephanie laetitia-bisset lana-burner lana-cox lana-wood lara-amour lara-roxx lara-stevens lataya-roxx latoya laura-clair laura-lazare laura-lion laura-may laura-orsolya laura-paouck laura-zanzibar lauren-black laurence-boutin lauren-montgomery laurien-dominique laurien-wilde laurie-smith lauryl-canyon lauryn-may leah-wilde lea-magic lea-martini leanna-foxxx lee-caroll leigh-livingston leilani lenora-bruce leslie-winston lesllie-bovee letizia-bruni lexi-lane lexi-matthews lezley-zen lia-fire liliane-gray liliane-lemieuvre lili-marlene lily-gilder lily-labeau lily-rodgers lily-valentine linda-shaw linda-vale linda-wong linnea-quigley lisa-bright lisa-de-leeuw lisa-k-loring lisa-lake lisa-melendez lisa-sue-corey lise-pinson little-oral-annie liza-dwyer liza-harper lizzy-borden logan-labrent lois-ayres lola-cait long-jean-silver loni-bunny loni-sanders loona-luxx lorelei-lee lorelei-rand lorena-sanchez lori-alexia lori-blue lorrie-lovett luci-diamond lucie-doll lucie-theodorova lucy-van-dam lydia-baum lynn-franciss lynn-lemay lynn-ray lynn-stevens lynx-canon lysa-thatcher madelina-ray madison-parker magdalena-lynn maggie-randall mai-lin mandi-wine mandy-bright mandy-malone mandy-may mandy-mistery mandy-starr marcia-minor maren margit-ojetz margitta-hofer margo-stevens margot-mahler mariah-cherry marianne-aubert maria-tortuga marie-anne marie-christine-chireix marie-christine-veroda marie-claude-moreau marie-dominique-cabannes marie-france-morel marie-luise-lusewitz marie-sharp marilyn-chambers marilyne-leroy marilyn-gee marilyn-jess marilyn-martyn marilyn-star marina-hedman marion-webb marita-ekberg marita-kemper marlena marlene-willoughby marry-queen martine-grimaud martine-schultz maryanne-fisher mary-hubay mary-ramunno mary-stuart mascha-mouton maud-kennedy mauvais-denoir maxine-tyler maya-black maya-france megan-leigh megan-martinez megan-reece mei-ling melanie-hotlips melanie-scott melba-cruz melinda-russell melissa-bonsardo melissa-del-prado melissa-golden melissa-martinez melissa-melendez melissa-monet mercedes-dragon mercedes-lynn merle-michaels mesha-lynn mia-beck mia-lina mia-smiles michele-raven michelle-aston michelle-ferrari michelle-greco michelle-maren michelle-maylene michelle-monroe micki-lynn mika-barthel mika-tan mikki-taylor mimi-morgan mindy-rae ming-toy miranda-stevens miss-bunny miss-meadow miss-pomodoro missy missy-graham missy-stone missy-vega misti-jane mistress-candice misty-anderson misty-dawn misty-rain misty-regan mona-lisa mona-page moni monica-baal monica-swinn monika-peta monika-sandmayr monika-unco monique-bruno monique-cardin monique-charell monique-demoan monique-gabrielle monique-la-belle morgan-fairlane morrigan-hel moxxie-maddron mulani-rivera mysti-may nadege-arnaud nadia-styles nadine-bronx nadine-proutnal nadine-roussial nadi-phuket nanci-suiter nancy-hoffman nancy-vee natacha-delyro natalia-wood natalli-diangelo natascha-throat natasha-skyler naudia-nyce nessa-devil nessy-grant nesty nicki-hunter nicky-reed nicole-berg nicole-bernard nicole-black nicole-grey nicole-london nicole-parks nicole-scott nicole-taylor nicolette-fauludi nicole-west nika-blond nika-mamic niki-cole nikita-love nikita-rush nikki-charm nikki-grand nikki-king nikki-knight nikki-randall nikki-rhodes nikki-santana nikki-steele nikki-wilde niko nina-cherry nina-deponca nina-hartley nina-preta oana-efria obaya-roberts olesja-derevko olga-cabaeva olga-conti olga-pechova olga-petrova olivia-alize olivia-del-rio olivia-flores olivia-la-roche olivia-outre ophelia-tozzi orchidea-keresztes orsolya-blonde paige-turner paisley-hunter pamela-bocchi pamela-jennings pamela-mann pamela-stanford pamela-stealt pandora paola-albini pascale-vital pat-manning pat-rhea patricia-dale patricia-diamond patricia-kennedy patricia-rhomberg patrizia-predan patti-cakes patti-petite paula-brasile paula-harlow paula-morton paula-price paula-winters pauline-teutscher penelope-pumpkins penelope-valentin petra-hermanova petra-lamas peyton-lafferty phaedra-grant pia-snow piper-fawn pipi-anderson porsche-lynn porsha-carrera precious-silver priscillia-lenn purple-passion queeny-love rachel-ashley rachel-love rachel-luv rachel-roxxx rachel-ryan rachel-ryder racquel-darrian rane-revere raven reagan-maddux rebecca-bardoux regan-anthony regine-bardot regula-mertens reina-leone reka-gabor renae-cruz renee-foxx renee-lovins renee-morgan renee-perez renee-summers renee-tiffany rhonda-jo-petty rikki-blake riley-ray rio-mariah rita-ricardo roberta-gemma roberta-pedon robin-byrd robin-cannes robin-everett robin-sane rochell-starr rosa-lee-kimball rosemarie roxanne-blaze roxanne-hall roxanne-rollan ruby-richards sabina-k sabre sabrina-chimaera sabrina-dawn sabrina-jade sabrina-johnson sabrina-love-cox sabrina-mastrolorenzi sabrina-rose sabrina-scott sabrina-summers sacha-davril sahara sahara-sands sai-tai-tiger samantha-fox samantha-ryan samantha-sterlyng samantha-strong samueline-de-la-rosa sandra-cardinale sandra-de-marco sandra-kalermen sandra-russo sandy-lee sandy-pinney sandy-reed sandy-samuel sandy-style sandy-summers sara-brandy-canyon sara-faye sarah-bernard sarah-cabrera sarah-hevyn sarah-mills sarah-shine sara-sloane sasha sasha-hollander sasha-ligaya sasha-rose satine-phoenix satin-summer savannah-stern savanna-jane scarlet-scarleau scarlet-windsor seka selena serena serena-south severine-amoux shana-evans shanna-mccullough shannon-kelly shannon-rush shantell-day sharon-da-vale sharon-kane sharon-mitchell shaun-michelle shawna-sexton shawnee-cates shay-hendrix shayne-ryder sheena-horne sheer-delight shelby-star shelby-stevens shelly-berlin shelly-lyons sheri-st-clair sheyla-cats shonna-lynn shyla-foxxx shy-love sierra-sinn sierra-skye sigrun-theil silver-starr silvia-bella silvia-saint silvie-de-lux silvy-taylor simone-west sindee-coxx sindy-lange sindy-shy siobhan-hunter skylar-knight skylar-price skyler-dupree smokie-flame smoking-mary-jane solange-shannon sonya-summers sophia-santi sophie-call sophie-duflot sophie-evans sophie-guers stacey-donovan stacy-lords stacy-moran stacy-nichols stacy-silver stacy-thorn starla-fox starr-wood stefania-bruni stella-virgin stephanie-duvalle stephanie-rage stephanie-renee stevie-taylor summer-knight summer-rose sunny-day sunset-thomas sunshine-seiber susan-hart susanne-brend susan-nero susi-hotkiss suzanne-mcbain suzan-nielsen suzie-bartlett suzie-carina suzi-sparks sweet-nice sweety-pie sybille-rossani sylvia-benedict sylvia-bourdon sylvia-brand sylvia-engelmann syreeta-taylor syren-de-mer syvette szabina-black szilvia-lauren tai-ellis taija-rae taisa-banx talia-james tamara-lee tamara-longley tamara-n-joy tamara-west tami-white tammy tammy-lee tammy-reynolds tania-lorenzo tantala-ray tanya-danielle tanya-fox tanya-foxx tanya-lawson tanya-valis tara-aire tasha-voux tatjana-belousova tatjana-skomorokhova tawnee-lee tawny-pearl tayla-rox taylor-wane teddi-austin teddi-barrett tera-bond tera-heart tera-joy teresa-may teresa-orlowski teri-diver teri-weigel terri-dolan terri-hall tess-ferre tess-newheart thais-vieira tia-cherry tianna tiara tiffany-blake tiffany-clark tiffany-duponte tiffany-rayne tiffany-rousso tiffany-storm tiffany-towers tiffany-tyler tiger-lily tigr timea-vagvoelgyi tina-blair tina-burner tina-evil tina-gabriel tina-loren tina-marie tina-russell tish-ambrose tommi-rose tonisha-mills topsy-curvey tori-secrets tori-sinclair tori-welles tracey-adams traci-lords traci-topps traci-winn tracy-duzit tracy-love tracy-williams tricia-devereaux tricia-yen trinity-loren trisha-rey trista-post trixie-tyler ultramax ursula-gaussmann ursula-moore uschi-karnat valentina valerie-leveau valery-hilton vanessa-chase vanessa-del-rio vanessa-michaels vanessa-ozdanic vanilla-deville velvet-summers veri-knotty veronica-dol veronica-hart veronica-hill veronica-rayne veronica-sage veronika-vanoza via-paxton vicky-lindsay vicky-vicci victoria-evans victoria-gold victoria-knight victoria-luna victoria-paris victoria-slick victoria-zdrok viper virginie-caprice vivian-valentine vivien-martines wendi-white wendy-divine whitney-banks whitney-fears whitney-wonders wonder-tracey wow-nikki xanthia-berstein yasmine-fitzgerald yelena-shieffer yvonne-green zara-whites zsanett-egerhazi zuzie-boobies

proportions, such as whales which are, by now, almost fully aquatic Mammals like Andrewsarchus were now at the top of the food chain and sharks were replaced by whales such as Basilosaurus as rulers of the seas The Late Eocene saw the rebirth of seasons, which caused the expansion of savanna like areas, along with the evolution of grass The Oligocene epoch spans from million to million years ago The Oligocene feature the expansion of grass which had led to many new species to evolve, including the first elephants, cats, dogs, marsupials and many other species still prevalent today Many other species of plants evolved in this period too, such as the evergreen trees A cooling period was still in effect and seasonal rains were as well Mammals still continued to grow larger and larger Paraceratherium, the largest land mammal to ever live evolved during this period, along with many other perissodactyls in an event known as the Grand Coupre Neogene edit Main article Neogene Animals of the Miocene Chalicotherium, Hyenadon, entelodont The Neogene spans from million to million years ago, and is the shortest geological period in the Phanerozoic It features two epochs the Miocene and the Pliocene The Miocene spans from to million years ago and is a period in which grass spreads further across, effectively dominating a large portion of the world, diminishing forests in the process Kelp forests evolved, leading to new species such as sea otters to evolve During this time, perissodactyls thrived, and evolved into many different varieties Alongside them were the apes, which evolved into a staggering species Overall, arid and mountainous land dominated most of the world, as did grazers The Tethys Sea finally closed with the creation of the Arabian Peninsula and in its wake left the Black, Red, Mediterranean and Caspian Seas This only increased aridity Many new plants evolved, and % of modern seed plants evolved in the mid Miocene The Pliocene ranges from to million years ago The Pliocene features dramatic climactic changes, which ultimately leads to modern species and plants The most dramatic are the formation of Panama, and the accumulation of ice at the poles, leading to a massive die off, India and Asia collide forming the Himalayas, the Rockies and Appalachian mountain ranges were formed, and the Mediterranean Sea dried up for the next several million years Along with these major geological events, Australopithecus evolves in Africa, beginning the human branch Also, with the isthmus of Panama, animals migrate across North and South America, wreaking havoc on the local ecology Climactic changes bring along savannas that are still continuing to spread across the world, Indian monsoons, deserts in East Asia, and the beginnings of the Sahara desert The earth's continents and seas move into their present shapes, and the world map hasn't changed much since Quaternary edit Main article Quaternary The Quaternary ranges from million to present day, and features modern animals, and dramatic climate changes and features two epochs the Pleistocene and the Holocene Mega fauna of the Pleistocene mammoths, cave lions, woolly rhino, Megaloceros, American horses Paleoclimatology in British spelling, palaeoclimatology is the study of changes in climate taken on the scale of the entire history of Earth It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within e g rocks, sediments, ice sheets, tree rings, corals, shells and microfossils it then uses these records to determine the past states of the Earth's various climate regions and its atmospheric system Studies of past changes in the environment and biodiversity often reflect on the current situation, and specifically the impact of climate on mass extinctions and biotic recovery Contents hide History Reconstructing ancient climates Ice Dendroclimatology Sclerochronology Limitations Notable climate events in Earth history History of the atmosphere Earliest atmosphere Second atmosphere Third atmosphere Climate during geological ages Precambrian climate Phanerozoic climate Quaternary climate Climate forcings Internal processes and forcings External forcings Mechanisms See also References Notes Bibliography External links History edit Main articles History of climate change science and Historical climatology The scientific study field of paleoclimate begun to form in the early th century, when discoveries about glaciations and natural changes in Earth's climate past helped to identify the process of the greenhouse effect Reconstructing ancient climates edit Palaeotemperature graphs compressed together Main article Proxy climate Paleoclimatologists employ a wide variety of techniques to deduce ancient climates Ice edit Mountain glaciers and the polar ice caps ice sheets provide much data in paleoclimatology Ice coring projects in the ice caps of Greenland and Antarctica have yielded data going back several hundred thousand years—over , years in the case of the EPICA project Air trapped within fallen snow becomes encased in tiny bubbles as the snow is compressed into ice in the glacier under the weight of later years' snow This trapped air has proven a tremendously valuable source for direct measurement of the composition of air from the time the ice was formed Layering can be observed due to seasonal pauses in ice accumulation and can be used to establish chronology associating specific depths of the core with ranges of time Changes in the layering thickness can be used to determine changes in precipitation or temperature Oxygen quantity changes d O in ice layers represent changes in average ocean surface temperature Water molecules containing the heavier O evaporate at a higher temperature than water molecules containing the normal Oxygen isotope The ratio of O to O will be higher as temperature increases It also depends on other factors such as the water's salinity and the volume of water locked up in ice sheets Various cycles in those isotope ratios have been detected Pollen has been observed in the ice cores and can be used to understand which plants were present as the layer formed Pollen is produced in abundance and its distribution is typically well understood A pollen count for a specific layer can be produced by observing the total amount of pollen categorized by type shape in a controlled sample of that layer Changes in plant frequency over time can be plotted through statistical analysis of pollen counts in the core Knowing which plants were present leads to an understanding of precipitation and temperature, and types of fauna present Palynology includes the study of pollen for these purposes Volcanic ash is contained in some layers, and can be used to establish the time of the layer's formation Each volcanic event distributed ash with a unique set of properties shape and color of particles, chemical signature Establishing the ash's source will establish a range of time to associate with layer of ice Dendroclimatology edit Main article Dendroclimatology Climatic information can be obtained through an understanding of changes in tree growth Generally, trees respond to changes in climatic variables by speeding up or slowing down growth, which in turn is generally reflected a greater or lesser thickness in growth rings Different species, however, respond to changes in climatic variables in different ways A tree ring record is established by compiling information from many living trees in a specific area Older intact wood that has escaped decay can extend the time covered by the record by matching the ring depth changes to contemporary specimens Using this method some areas have tree ring records dating back a few thousand years Older wood not connected to a contemporary record can be dated generally with radiocarbon techniques A tree ring record can be used to produce information regarding precipitation, temperature, hydrology, and fire corresponding to a particular area On a longer time scale, geologists must refer to the sedimentary record for data Sedimentary content Sediments, sometimes lithified to form rock, may contain remnants of preserved vegetation, animals, plankton or pollen, which may be characteristic of certain climatic zones Biomarker molecules such as the alkenones may yield information about their temperature of formation Chemical signatures, particularly Mg Ca ratio of calcite in Foraminifera tests, can be used to reconstruct past temperature Isotopic ratios can provide further information Specifically, the d O record responds to changes in temperature and ice volume, and the d C record reflects a range of factors, which are often difficult to disentangle Sea floor core sample labelled to identify the exact spot on the sea floor where the sample was taken Slight variations in location can make a significant difference in the chemical and biological composition of the sediment sample Sedimentary facies On a longer time scale, the rock record may show signs of sea level rise and fall further, features such as fossilised sand dunes can be identified Scientists can get a grasp of long term climate by studying sedimentary rock going back billions of years The division of earth history into separate periods is largely based on visible changes in sedimentary rock layers that demarcate major changes in conditions Often these include major shifts in climate Sclerochronology edit Corals see also sclerochronology Coral rings are similar to tree rings, except they respond to different things, such as the water temperature, freshwater influx, pH changes, and wave action From this source, certain equipment can be used to derive the sea surface temperature and water salinity from the past few centuries The d O of coralline red algae provides a useful proxy of the combined sea surface temperature and sea surface salinity at high latitudes and the tropics, where many traditional techniques are limited Limitations edit A multinational consortium, the European Project for Ice Coring in Antarctica EPICA , has drilled an ice core in Dome C on the East Antarctic ice sheet and retrieved ice which dates to roughly , years ago The international ice core community has, under the auspices of International Partnerships in Ice Core Sciences IPICS , defined a priority project to obtain the oldest possible ice core record from Antarctica, an ice core record reaching back to or towards million years ago The deep marine record, the source of most isotopic data, only exists on oceanic plates, which are eventually subducted — the oldest remaining material is million years old Older sediments are also more prone to corruption by diagenesis Resolution and confidence in the data decrease over time Notable climate events in Earth history edit See also List of periods and events in climate history, Geologic time scale and History of Earth Knowledge of precise climatic events decreases as the record goes further back in time Some notable climate events Faint young Sun paradox start Huronian glaciation ~ Mya Earth completely covered in ice probably due to Great Oxygenation Event Later Neoproterozoic Snowball Earth ~ Mya, precursor to the Cambrian Explosion Andean Saharan glaciation ~ Mya Carboniferous Rainforest Collapse ~ Mya Permian–Triassic extinction event Mya Oceanic Anoxic Events ~ Mya, Mya, and others Cretaceous–Paleogene extinction event Mya Paleocene–Eocene Thermal Maximum Paleocene–Eocene, Mya Younger Dryas The Big Freeze ~ , BC Holocene climatic optimum ~ – BC Climate changes of – AD Medieval warm period – Little Ice Age – Year Without a Summer History of the atmosphere edit See also Atmosphere of Earth and History of Earth Earliest atmosphere edit The first atmosphere would have consisted of gases in the solar nebula, primarily hydrogen In addition, there would probably have been simple hydrides such as those now found in gas giants like Jupiter and Saturn, notably water vapor, methane and ammonia As the solar nebula dissipated, these gases would have escaped, partly driven off by the solar wind Second atmosphere edit The next atmosphere, consisting largely of nitrogen plus carbon dioxide and inert gases, was produced by outgassing from volcanism, supplemented by gases produced during the late heavy bombardment of Earth by huge asteroids A major part of carbon dioxide emissions were soon dissolved in water and built up carbonate sediments Water related sediments have been found dating from as early as billion years ago About billion years ago, nitrogen was the major part of the then stable second atmosphere An influence of life has to be taken into account rather soon in the history of the atmosphere, because hints of early life forms are to be found as early as billion years ago The fact that this is not perfectly in line with the % lower solar radiance compared to today of the early Sun has been described as the faint young Sun paradox The geological record however shows a continually relatively warm surface during the complete early temperature record of Earth with the exception of one cold glacial phase about billion years ago In the late Archaean eon an oxygen containing atmosphere began to develop, apparently from photosynthesizing cyanobacteria see Great Oxygenation Event which have been found as stromatolite fossils from billion years ago The early basic carbon isotopy isotope ratio proportions is very much in line with what is found today, suggesting that the fundamental features of the carbon cycle were established as early as billion years ago Third atmosphere edit The constant re arrangement of continents by plate tectonics influences the long term evolution of the atmosphere by transferring carbon dioxide to and from large continental carbonate stores Free oxygen did not exist in the atmosphere until about billion years ago during the Great Oxygenation Event and its appearance is indicated by the end of the banded iron formations Before this time, any oxygen produced by photosynthesis was consumed by oxidation of reduced materials, notably iron Molecules of free oxygen did not start to accumulate in the atmosphere until the rate of production of oxygen began to exceed the availability of reducing materials This point signifies a shift from a reducing atmosphere to an oxidizing atmosphere O showed major variations until reaching a steady state of more than % by the end of the Precambrian The following time span was the Phanerozoic eon, during which oxygen breathing metazoan life forms began to appear The amount of oxygen in the atmosphere has fluctuated over the last million years, reaching a peak of about % around million years ago, significantly higher than today's % Two main processes govern changes in the atmosphere Plants use carbon dioxide from the atmosphere, releasing oxygen Breakdown of pyrite and volcanic eruptions release sulfur into the atmosphere, which oxidizes and hence reduces the amount of oxygen in the atmosphere However, volcanic eruptions also release carbon dioxide, which plants can convert to oxygen The exact cause of the variation of the amount of oxygen in the atmosphere is not known Periods with much oxygen in the atmosphere are associated with rapid development of animals Today's atmosphere contains % oxygen, which is high enough for this rapid development of animals Currently, anthropogenic greenhouse gases are accumulating in the atmosphere, which is the main cause of global warming Climate during geological ages edit See also Timeline of glaciation Timeline of glaciations, shown in blue The Huronian glaciation, is the first known glaciation in Earth's history, and lasted from million years ago The Cryogenian glaciation lasted from million years ago The Andean Saharan glaciation lasted from – million years ago The Karoo glaciation lasted from – million years ago The Quaternary glaciation is the current glaciation period and begun million years ago Precambrian climate edit Main article Precambrian The climate of the late Precambrian showed some major glaciation events spreading over much of the earth At this time the continents were bunched up in the Rodinia supercontinent Massive deposits of tillites are found and anomalous isotopic signatures are found, which gave rise to the Snowball Earth hypothesis As the Proterozoic Eon drew to a close, the Earth started to warm up By the dawn of the Cambrian and the Phanerozoic, life forms were abundant in the Cambrian explosion with average global temperatures of about °C Phanerozoic climate edit Main article Phanerozoic million years of climate change Major drivers for the preindustrial ages have been variations of the sun, volcanic ashes and exhalations, relative movements of the earth towards the sun and tectonically induced effects as for major sea currents, watersheds and ocean oscillations In the early Phanerozoic, increased atmospheric carbon dioxide concentrations have been linked to driving or amplifying increased global temperatures Royer et al found a climate sensitivity for the rest of the Phanerozoic which was calculated to be similar to today's modern range of values The difference in global mean temperatures between a fully glacial Earth and an ice free Earth is estimated at approximately °C, though far larger changes would be observed at high latitudes and smaller ones at low latitudes citation needed One requirement for the development of large scale ice sheets seems to be the arrangement of continental land masses at or near the poles The constant rearrangement of continents by plate tectonics can also shape long term climate evolution However, the presence or absence of land masses at the poles is not sufficient to guarantee glaciations or exclude polar ice caps Evidence exists of past warm periods in Earth's climate when polar land masses similar to Antarctica were home to deciduous forests rather than ice sheets The relatively warm local minimum between Jurassic and Cretaceous goes along with an increase

of subduction and mid ocean ridge volcanism due to the breakup of the Pangea supercontinent Superimposed on the long term evolution between hot and cold climates have been many short term fluctuations in climate similar to, and sometimes more severe than, the varying glacial and interglacial states of the present ice age Some of the most severe fluctuations, such as the Paleocene Eocene Thermal Maximum, may be related to rapid climate changes due to sudden collapses of natural methane clathrate reservoirs in the oceans citation needed A similar, single event of induced severe climate change after a meteorite impact has been proposed as reason for the Cretaceous–Paleogene extinction event Other major thresholds are the Permian Triassic, and Ordovician Silurian extinction events with various reasons suggested Quaternary climate edit Main article Quaternary See also List of large scale temperature reconstructions of the last , years Ice core data for the past , years Note length of glacial cycles averages ~ , years Blue curve is temperature, green curve is CO , and red curve is windblown glacial dust loess Today's date is on the left side of the graph The Quaternary sub era includes the current climate There has been a cycle of ice ages for the past – million years starting before the Quaternary in the late Neogene Period Note in the graphic on the right the strong , year periodicity of the cycles, and the striking asymmetry of the curves This asymmetry is believed to result from complex interactions of feedback mechanisms It has been observed that ice ages deepen by progressive steps, but the recovery to interglacial conditions occurs in one big step The graph below shows the temperature change over the past years, from various sources The thick black curve is an average Holocene Temperature Variations Climate forcings edit Radiative forcings, IPCC Main article Climate change § Causes The climate forcing is the difference of radiant energy sunlight received by the Earth and the outgoing longwave radiation back to space The radiative forcing is quantified based on the CO amount in the tropopause, in units of watts per square meter to the Earth's surface Dependent on the radiative balance of incoming and outgoing energy, the Earth either warms up or cools down Earth radiative balance originates from changes in solar insolation and the concentrations of greenhouse gases and aerosols Climate change may be due to internal processes in Earth sphere's and or following external forcings Internal processes and forcings edit The Earth's climate system involves the study of the atmosphere, biosphere, cryosphere, hydrosphere, and lithosphere, and the sum of these processes from Earth sphere's is considered the processes affecting the climate Greenhouse gases act as the internal forcing of the climate system Particular interests in climate science and paleoclimatology focuses on the study of Earth climate sensitivity, in response to the sum of forcings Examples Thermohaline circulation Hydrosphere Life Biosphere External forcings edit The Milankovitch cycles determine Earth distance and position to the Sun The solar insolation, is the total amount of solar radiation received by Earth Volcanic eruptions, are considered an external forcing Human changes of the composition of the atmosphere or land use Dendroclimatology is the science of determining past climates from trees primarily properties of the annual tree rings Tree rings are wider when conditions favor growth, narrower when times are difficult Other properties of the annual rings, such as maximum latewood density MXD have been shown to be better proxies than simple ring width Using tree rings, scientists have estimated many local climates for hundreds to thousands of years previous By combining multiple tree ring studies sometimes with other climate proxy records , scientists have estimated past regional and global climates see Temperature record of the past years Contents hide Advantages Limitations Confounding factors Climate factors Non climate factors Non linear effects Botanical inferences to correct for confounding factors Divergence problem Geographic coverage Annular resolution Collection difficulties Other measurements Notes See also References External links Advantages edit Tree rings are especially useful as climate proxies in that they can be well dated via matching of the rings from sample to sample, i e dendrochronology This allows extension backwards in time using deceased tree samples, even using samples from buildings or from archeological digs Another advantage of tree rings is that they are clearly demarked in annual increments, as opposed to other proxy methods such as boreholes Furthermore, tree rings respond to multiple climatic effects temperature, moisture, cloudiness , so that various aspects of climate not just temperature can be studied However, this can be a double edged sword as discussed in Climate factors Limitations edit Along with the advantages of dendroclimatology are some limitations confounding factors, geographic coverage, annular resolution, and collection difficulties The field has developed various methods to partially adjust for these challenges Confounding factors edit There are multiple climate and non climate factors as well as nonlinear effects that impact tree ring width Methods to isolate single factors of interest include botanical studies to calibrate growth influences and sampling of limiting stands those expected to respond mostly to the variable of interest Climate factors edit Climate factors that affect trees include temperature, precipitation, sunlight, and wind To differentiate among these factors, scientists collect information from limiting stands An example of a limiting stand is the upper elevation treeline here, trees are expected to be more affected by temperature variation which is limited than precipitation variation which is in excess Conversely, lower elevation treelines are expected to be more affected by precipitation changes than temperature variation This is not a perfect work around as multiple factors still impact trees even at the limiting stand , but it helps In theory, collection of samples from nearby limiting stands of different types e g upper and lower treelines on the same mountain should allow mathematical solution for multiple climate factors However, this method is rarely used Non climate factors edit Non climate factors include soil, tree age, fire, tree to tree competition, genetic differences, logging or other Carbon , C, or radiocarbon, is a radioactive isotope of carbon with a nucleus containing protons and neutrons Its presence in organic materials is the basis of the radiocarbon dating method pioneered by Willard Libby and colleagues to date archaeological, geological and hydrogeological samples Carbon was discovered on February , by Martin Kamen and Sam Ruben at the University of California Radiation Laboratory in Berkeley Its existence had been suggested by Franz Kurie in There are three naturally occurring isotopes of carbon on Earth % of the carbon is carbon , % is carbon , and carbon occurs in trace amounts, i e , making up about or atoms per atoms of the carbon in the atmosphere The half life of carbon is , ± years Carbon decays into nitrogen through beta decay A gram of carbon containing atom of carbon per atoms will emit citation needed beta rays per second The primary natural source of carbon on Earth is cosmic ray action on nitrogen in the atmosphere, and it is therefore a cosmogenic nuclide However, open air nuclear testing between – contributed to this pool The different isotopes of carbon do not differ appreciably in their chemical properties This is used in chemical and biological research, in a technique called carbon labeling carbon atoms can be used to replace nonradioactive carbon, in order to trace chemical and biochemical reactions involving carbon atoms from any given organic compound Contents hide Radioactive decay and detection Radiocarbon dating Origin Natural production in the atmosphere Other carbon sources Formation during nuclear tests Occurrence Dispersion in the environment Total inventory In fossil fuels In the human body See also References Further reading External links Radioactive decay and detection edit Carbon goes through radioactive beta decay mathrm{~^{ }_{ }C} rightarrow mathrm{~^{ }_{ }N}+ e^ + bar{ nu}_e By emitting an electron and an electron antineutrino, one of the neutrons in the carbon atom decays to a proton and the carbon half life of years decays into the stable non radioactive isotope nitrogen The emitted beta particles have a maximum energy of keV, while their average clarification needed energy is keV These are relatively low energies the maximum distance traveled is estimated to be cm in air and mm in body tissue The fraction of the radiation transmitted through the dead skin layer is estimated to be Small amounts of carbon are not easily detected by typical Geiger–Müller G M detectors it is estimated that G M detectors will not normally detect contamination of less than about disintegration per minute µCi Liquid scintillation counting is the preferred method The G M counting efficiency is estimated to be % The half distance layer in water is mm Radiocarbon dating edit Main article Radiocarbon dating Radiocarbon dating is a radiometric dating method that uses C to determine the age of carbonaceous materials up to about , years old The technique was developed by Willard Libby and his colleagues in during his tenure as a professor at the University of Chicago Libby estimated that the radioactivity of exchangeable carbon would be about disintegrations per minute dpm per gram of pure carbon, and this is still used as the activity of the modern radiocarbon standard In , Libby was awarded the Nobel Prize in chemistry for this work One of the frequent uses of the technique is to date organic remains from archaeological sites Plants fix atmospheric carbon during photosynthesis, so the level of C in plants and animals when they die approximately equals the level of C in the atmosphere at that time However, it decreases thereafter from radioactive decay, allowing the date of death or fixation to be estimated The initial C level for the calculation can either be estimated, or else directly compared with known year by year data from tree ring data dendrochronology up to , years ago using overlapping data from live and dead trees in a given area , or else from cave deposits speleothems , back to about , years before the present A calculation or more accurately a direct comparison of carbon levels in a sample, with tree ring or cave deposit carbon levels of a known age, then gives the wood or animal sample age since formation Origin edit Natural production in the atmosphere edit Formation of carbon Decay of carbon The equal equation is for living organisms, and the unequal one is for dead organisms, in which the C then decays See Carbon is produced in the upper layers of the troposphere and the stratosphere by thermal neutrons absorbed by nitrogen atoms When cosmic rays enter the atmosphere, they undergo various transformations, including the production of neutrons The resulting neutrons n participate in the following reaction n + N ? C + p The highest rate of carbon production takes place at altitudes of to km , to , ft and at high geomagnetic latitudes As of , the rate of C production was poorly known – while the reaction can be modelled and the results agree with the global carbon budget that can be used to backtrack, attempts to directly measure the production rate had not agreed with these models very well Production rates vary because of changes to the cosmic ray flux incident, such as supernovae, and due to variations in the Earth's magnetic field The latter can create significant variations in C production rates, although the changes of the carbon cycle can make these effects difficult to tease out The natural atmospheric yield of C has been estimated to be about atoms C per meter square of the surface of the earth per second, resulting in the global production rate of about PBq a Another estimate of the average production rate gives a value of atoms m- s- More recent work, however, suggests that the use of outdated cosmic ray spectra has led to an overestimation of C yield and revised the estimate down to between to atoms C per meter square Occasional spikes are possible for example, there is evidence for an unusual fold increase of the production rate in AD – Other carbon sources edit Carbon can also be produced by other neutron reactions, including in particular C n,gamma C and O n,alpha C with thermal neutrons, and N n,d C and O n, He C with fast neutrons The most notable routes for C production by thermal neutron irradiation of targets e g , in a nuclear reactor are summarized in the table Carbon may also be radiogenic cluster decay of Ra, Ra, Ra However, this origin is extremely rare C production routes Parent isotope Natural abundance, % Cross section for thermal neutron capture, b Reaction N N n,p C C C n,? C O O n,a C Formation during nuclear tests edit Atmospheric C, New Zealand and Austria The New Zealand curve is representative for the Southern Hemisphere, the Austrian curve is representative for the Northern Hemisphere Atmospheric nuclear weapon tests almost doubled the concentration of C in the Northern Hemisphere The above ground nuclear tests that occurred in several countries between and see nuclear test list dramatically increased the amount of carbon in the atmosphere and subsequently in the biosphere after the tests ended, the atmospheric concentration of the isotope began to decrease One side effect of the change in atmospheric carbon is that this has enabled some options e g bomb pulse dating for determining the birth year of an individual, in particular, the amount of carbon in tooth enamel, or the carbon concentration in the lens of the eye Occurrence edit Dispersion in the environment edit After production in the upper atmosphere, the carbon atoms react rapidly to form mostly about % CO carbon monoxide , which subsequently oxidizes at a slower rate to form CO , radioactive carbon dioxide The gas mixes rapidly and becomes evenly distributed throughout the atmosphere the mixing timescale in the order of weeks Carbon dioxide also dissolves in water and thus permeates the oceans, but at a slower rate The atmospheric half life for removal of CO has been estimated to be roughly to years in the northern hemisphere The transfer between the ocean shallow layer and the large reservoir of bicarbonates in the ocean depths occurs at a limited rate In the activity of C was Bq per kg carbon of fresh terrestrial biomatter, close to the values before atmospheric nuclear testing Bq kg C Total inventory edit The inventory of carbon in Earth's biosphere is about megacuries EBq , of which most is in the oceans The following inventory of carbon has been given Global inventory ~ PBq about t Ammonia or azane is a compound of nitrogen and hydrogen with the formula NH It is a colourless gas with a characteristic pungent smell Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceuticals and is used in many commercial cleaning products Although common in nature and in wide use, ammonia is both caustic and hazardous in its concentrated form The global industrial production of ammonia for was anticipated to be , , tonnes , , long tons , , short tons , a % increase over the estimated global output of , , tonnes , , long tons , , short tons NH boils at - °C - °F at a pressure of one atmosphere, so the liquid must be stored under pressure or at low temperature Household ammonia or ammonium hydroxide is a solution of NH in water The concentration of such solutions is measured in units of the Baumé scale density , with degrees baumé about % by weight ammonia at °C or °F being the typical high concentration commercial product Contents hide Natural occurrence Properties Structure Amphotericity Self dissociation Combustion Formation of other compounds Ammonia as a ligand Detection and determination Ammonia in solution Gaseous ammonia Ammoniacal nitrogen NH N History Uses Fertilizer Precursor to nitrogenous compounds Cleaner Fermentation Antimicrobial agent for food products Minor and emerging uses Refrigeration – R For remediation of gaseous emissions As a fuel As a stimulant Textile Lifting gas Woodworking Safety precautions Toxicity Aquaculture Storage information Household use Laboratory use of ammonia solutions Laboratory use of anhydrous ammonia gas or liquid Synthesis and production Liquid ammonia as a solvent Solubility of salts Solutions of metals Redox properties of liquid ammonia Ammonia's role in biological systems and human disease Biosynthesis In physiology Excretion In astronomy Interstellar space Interstellar formation mechanisms Interstellar destruction mechanisms Single antenna detections Interferometric studies Infrared detections Observations of nearby dark clouds UC HII regions Extragalactic detection See also Notes References Further reading External links Natural occurrence edit Ammonia is found in trace quantities in the atmosphere, being produced from the putrefaction decay process of nitrogenous animal and vegetable matter Ammonia and ammonium salts are also found in small quantities in rainwater, whereas ammonium chloride sal ammoniac , and ammonium sulfate are found in volcanic districts crystals of ammonium bicarbonate have been found in Patagonian guano The kidneys secrete ammonia to neutralize excess acid Ammonium salts are found distributed through fertile soil and in seawater Ammonia is also found throughout the Solar System on Pluto, Mars, Jupiter, Saturn, Uranus, and Neptune Substances containing ammonia, or those that are similar to it, are called ammoniacal Properties edit Ammonia is a colourless gas with a characteristic pungent smell It is lighter than air, its density being times that of air It is easily liquefied due to the strong hydrogen bonding between molecules the liquid boils at - °C - °F , and freezes at - °C - °F to white crystals Ammonia may be conveniently deodorized by reacting it with either sodium bicarbonate or acetic acid Both of these reactions form an odourless ammonium salt Solid The crystal symmetry is cubic, Pearson symbol cP , space group P No , lattice constant nm Liquid Liquid ammonia possesses strong ionising powers reflecting its high e of Liquid ammonia has a very high standard enthalpy change of vaporization kJ mol, cf water kJ mol, methane kJ mol, phosphine kJ mol and can therefore be used in laboratories in uninsulated vessels without additional refrigeration See liquid ammonia as a solvent Solvent properties Ammonia is miscible with water In an aqueous solution, it can be expelled by boiling The aqueous solution of ammonia is basic The maximum concentration of ammonia in water a saturated solution has a density of g cm and is often known as ' ammonia' Ammonia does not burn readily or sustain combustion, except under narrow fuel to air mixtures of – % air Combustion When mixed with oxygen, it burns with a pale yellowish green flame At high temperature and in the presence of a suitable catalyst, ammonia is decomposed into its constituent elements Ignition occurs when chlorine is passed into ammonia, forming nitrogen and hydrogen chloride if chlorine is present in excess, then the highly explosive nitrogen trichloride NCl is also formed Structure edit The ammonia molecule has a trigonal pyramidal shape as predicted by the valence shell electron pair repulsion theory VSEPR theory with an experimentally determined bond angle of ° The central nitrogen atom has five outer electrons with an additional electron from each hydrogen atom This gives a total of eight electrons, or four electron pairs that are arranged tetrahedrally Three of these electron pairs are used as bond pairs, which leaves one lone pair of electrons The lone pair of electrons repel more strongly than bond pairs, therefore the bond angle is not °, as expected for a regular tetrahedral arrangement, but ° The nitrogen atom in the molecule has a lone electron pair, which makes ammonia a base, a proton acceptor This shape gives the molecule a dipole moment and makes it polar The molecule's polarity and, especially, its ability to form hydrogen bonds, makes ammonia highly miscible with water Ammonia is moderately basic, a M aqueous solution has a pH of and if a strong acid is added to such a solution until the solution is neutral pH , % of the ammonia molecules are protonated Temperature and salinity also affect the proportion of NH + The latter has the shape of a regular tetrahedron and is isoelectronic with methane The ammonia molecule readily undergoes nitrogen inversion at room temperature a useful analogy is an umbrella turning itself inside out in a strong wind The energy barrier to this inversion is kJ mol, and the resonance frequency is GHz, corresponding to microwave radiation of a wavelength of cm The absorption at this frequency was the first microwave spectrum to be observed Amphotericity edit One of the most characteristic properties of ammonia is its basicity Ammonia is considered to be a weak base It combines with acids to form salts thus with hydrochloric acid it forms ammonium chloride sal ammoniac with nitric acid, ammonium nitrate, etc Perfectly dry ammonia will not combine with perfectly dry hydrogen chloride moisture is necessary to bring about the reaction As a demonstration experiment, opened bottles of concentrated ammonia and hydrochloric acid produce clouds of ammonium chloride, which seem to appear out of nothing as the salt forms where the two diffusing clouds of molecules meet, somewhere between the two bottles NH + HCl ? NH Cl The salts produced by the action of ammonia on acids are known as the ammonium salts and all contain the ammonium ion NH + Although ammonia is well known as a weak base, it can also act as an extremely weak acid It is a protic substance and is capable of formation of amides which contain the NH - ion For example, lithium dissolves in liquid ammonia to give a solution of lithium amide Li + NH ? LiNH + H Self dissociation edit Like water, ammonia undergoes molecular autoionisation to form its acid and base conjugates NH aq is in equilibrium with NH+ aq + NH- aq At standard pressure and temperature, K NH+ NH- - Combustion edit The combustion of ammonia to nitrogen and water is exothermic NH + O ? N + H O g ?H°r - kJ mol The standard enthalpy change of combustion, ?H°c, expressed per mole of ammonia and with condensation of the water formed, is - kJ mol Dinitrogen is the thermodynamic product of combustion all nitrogen oxides are unstable with respect to N and O , which is the principle behind the catalytic converter Nitrogen oxides can be formed as kinetic products in the presence of appropriate catalysts, a reaction of great industrial importance in the production of nitric acid NH + O ? NO + H O A subsequent reaction leads to NO NO + O ? NO The combustion of ammonia in air is very difficult in the absence of a catalyst such as platinum gauze , because the temperature of the flame is usually lower than the ignition temperature of the ammonia–air mixture The flammable range of ammonia in air is – % Formation of other compounds edit In organic chemistry, ammonia can act as a nucleophile in substitution reactions Amines can be formed by the reaction of ammonia with alkyl halides, although the resulting NH group is also nucleophilic and secondary and tertiary amines are often formed as byproducts An excess of ammonia helps minimise multiple substitution, and neutralises the hydrogen halide formed Methylamine is prepared commercially by the reaction of ammonia with chloromethane, and the reaction of ammonia with bromopropanoic acid has been used to prepare racemic alanine in % yield Ethanolamine is prepared by a ring opening reaction with ethylene oxide the reaction is sometimes allowed to go further to produce diethanolamine and triethanolamine Amides can be prepared by the reaction of ammonia with carboxylic acid derivatives Acyl chlorides are the most reactive, but the ammonia must be present in at least a twofold excess to neutralise the hydrogen chloride formed Esters and anhydrides also react with ammonia to form amides Ammonium salts of carboxylic acids can be dehydrated to amides so long as there are no thermally sensitive groups present temperatures of – °C are required The hydrogen in ammonia is capable of replacement by metals, thus magnesium burns in the gas with the formation of magnesium nitride Mg N , and when the gas is passed over heated sodium or potassium, sodamide, NaNH , and potassamide, KNH , are formed Where necessary in substitutive nomenclature, IUPAC recommendations prefer the name azane to ammonia hence chloramine would be named chloroazane in substitutive nomenclature, not chloroammonia Pentavalent ammonia is known as ? amine, or more commonly, ammonium hydride This crystalline solid is only stable under high pressure, and decomposes back into trivalent ammonia and hydrogen gas at normal conditions This substance was once investigated as a possible solid rocket fuel in Ammonia as a ligand edit Main article Metal ammine complex Ball and stick model of the tetraamminediaquacopper II cation, Cu NH H O + Ammonia can act as a ligand in transition metal complexes It is a pure s donor, in the middle of the spectrochemical series, and shows intermediate hard soft behaviour For historical reasons, ammonia is named ammine in the nomenclature of coordination compounds Some notable ammine complexes include tetraamminediaquacopper II Cu NH H O + , a dark blue complex formed by adding ammonia to a solution of copper II salts Tetraamminediaquacopper II hydroxide is known as Schweizer's reagent, and has the remarkable ability to dissolve cellulose Diamminesilver I Ag NH + is the active species in Tollens' reagent Formation of this complex can also help to distinguish between precipitates of the different silver halides silver chloride AgCl is soluble in dilute M ammonia solution, silver bromide AgBr is only soluble in concentrated ammonia solution, whereas silver iodide AgI is insoluble in aqueous ammonia Ammine complexes of chromium III were known in the late th century, and formed the basis of Alfred Werner's revolutionary theory on the structure of coordination compounds Werner noted only two isomers fac and mer of the complex CrCl NH could be formed, and concluded the ligands must be arranged around the metal ion at the vertices of an octahedron This proposal has since been confirmed by X ray crystallography An ammine ligand bound to a metal ion is markedly more acidic than a free ammonia molecule, although deprotonation in aqueous