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Astrobiology Lesson4 “LifeonEarthasareference” Theancientideas ArewealoneintheUniverse? ArewealoneintheUniverse? The sky is always there. We can only speculate in how , slowly, questions about the lights in the sky started to be formulated The Chinese started keeping records 5000 years ago The Babylonians could both record and predict eclipses of the Sun and Moon with precision Followed by Mayans in central America a few hundred years later ArewealoneintheUniverse? Thegreekculturebeginstoariseabout800 B.C.Andiswellestablished~500B.C. Westernphilosophybeginswith Thales!(Aristotles,BertrandRussel) Thalespredictedthesolareclipseof May28,585BC HealsoaskedthequesPon:“Whatis theUniversemadeof? Thales'rejecPonofmythologicalexplanaPons becameanessenPalideaforthescienPfic evoluPon ThalesfromMiletosc.624– c.546B.C. EarlyGreekscience By500B.C.Greeceiswellestablishedatthe crossroadsbetweenAfrica,AsiaandEurope Thalescosmologicalviewinvolvedaflat EarthfloaPnginaninfiniteocean ThalesledtoPlato428–384B.C.è Each philosopher introduced new ideas arguing in a scientific way, without invoking super-natural phenomena. Mathematics was introduced in a serious way WholedtoAristotele384– 322B.C. EarlyGreekscience Anaximander,astudentofThales(610–547 B.C.)introducedthecelesPalsphere,based ontheapparentrotaPonoftheskyaround thepolestar. Around500B.C.Pythagoras(560– 480B.C.)taughtthattheEarthis round èThegeocentricmodel The planets had been recognised as special already before the Greek science appeared (planet ~ “wanderer” EarlyGreekscience SunandMooneachhadtheirowncelesPalspheres, separatefromthestellarone,androtaPngattheirown velociPesbuttheplanetswerepeculiarwithstrange movements Ptolemy(ca100to170A.D.)cameupwithamodelthatwouldlastfor1500years. Theepicyclicalmodel. EarlyGreekscience ThePtolemaianmodelcametobethe acceptedoneunPl1543A.D.,butalready around260B.C.,AristarchusofSamos(c. 310–230B.C.)hadcomeupwithamodel w/oepicyclesèTheSunisthecentre NobodyknowhowAristarchushitontheideathatthe Earthtogetherwiththeotherplanetsmovearoundthe Sun We know he actually calculated the size of the Sun and the Moon. He also believed that the stars were other Suns EarlyGreekscience ThegreekscienPficclimatewasveryferPle andallowedformanyhypotheses. AlreadyatthePmeofThales,thegreekphilosophers realisedtheanswerhadimplicaPonsw.r.t.Lifeelsewhere. Thales student Anaximander imagined that the world was not based on water, but instead on a “mystic” element called apeiron which means “infinite”. From the “infinite” other worlds could appear and disappear. He made no claims about other life but other “Earths” could exist. Democritos postulated atoms and since worlds appeared from random actions of atoms both worlds and life could appear This lead to Epicuros idea about: There are other worlds both like and unlike this world of ours... We must beieive that in all worlds there are living creatures and plants and other things we see in this world • ButAristotelehadadifferentideabasedonthefour elements:earth,fire,water,air • TheEarthrestedin“thecentralplace”because“firejut upwardsintotheskyawayfromthecentre”,andearthfellto thecentre • Aristotelediscardedthe“atomists”aroundDemocritos • AristoteleconcludedthattheEarthisinthecentreofthe Universe,andthatallotherbodiesorbitit.Earthbeingunique couldbetheonlyhomeforlife!Basedonthewrongphysics thisidealastedcloseto2millennia • “Theworldmustbeunique....Therecannotbeseveralworlds” AninteresPngsideissue.... • Howmanycorrectideashavebeendiscardedover theyears? • Makingitnecessarytoinventtheconceptsagain? • AnindicaPonistheAnPkyteramechanism • TheAnthikyteramechanismisanancientanalog computer,thatcanpredictcelesPalbodiesposiPons, movements,andeclipsesformanycenturies forwardsandbackwards • Itwasrecoveredin1900–01fromashipwreckatthe GreekislandofAnPkythera • ItsconstrucPonisdatedto150–100B.C. • Nothinglikeitwouldbeseenfor1600years Intermission • Discussion:Whydomankindstophere?Foralmosta thousandyears(aherthefirstChrisPanculturalevoluPon) scienceisthreadingwater. • Alexander(theGreat)foundedthelibrary(andthetown)in Alexandria~330B.C.For700yearsitwastheworldspreeminentuniversity–unPlthemobcameinthe5:thcentury andburnedittotheground.AnPintellectuanism?Religious fundamentalism? • TheIslamicscholarsduringtheMiddleAgeskeptintouch withHinduscienPsts,ideasfromChinaèSyntheseofthe GreekworldwhichwhenEastRomefellin1453movedwest intoEurope TheCopernicanrevoluPon,Enlightenmentvs religion • Theknowledge“kept”bytheIslamicscholarsnow resurfaceinmonestariesandlibrariesacrossEurope • CriPcalthoughthadbeenappearingforafew hundredyearsbutnowitisapproachinga“boiling point” • ItsPmeforarevoluPon The birth of the belief in other worlds Theanciantideasof There areinfiniteworldsbothlike andunlikethisworldofours… Epicurus(c300BC) ...andBruno:“Thereare countlesssunsandcountless earthsallrotaPngaroundtheir sunsinexactlythesamewayas thesevenplanetsofoursystem… arenowdebatedagainby…Thecountlessworldsinthe universearenoworseandnoless falseanddamnable… G.Galiliei(born1564) inhabitedthanourEarth GiordanoBruno,1584 inDeL'infinitoUniversoEMondi Into this appears Nicholas Copernicus from Torun (1473 – 1543) NicholasCopernicus publisheshisbookDe revolutionibus orbium coelestium in 1543 CopernicusstudiedLaw, MedicineandAstronomyin PolandandItaly.Heworked inmanyfieldsincluding economicsandtranslaPonof ancienttexts HeprobablychoseAristarchus Sun-centeredmodelbecauseit wassimplerwhentryingtoexplain theretrogrademoPononthesky oftheplanets He also noted the errors in the positions of stars when comparing observations with ancient tables • ButhewasahesitantrevoluPonary.Inspiteofbeing givenassuranceshedidnotpublishthe“De revoluBonibus”unPlwhenhewasalreadydying. Withoutthesupportofayoungastronomer, “RhePcus”itmightneverhavebeenpublished • Koestlerwhohaswrilenaveryreadablebook (“Sleepwalkers”)aboutTheancients,Copernicus, Brahe,KeplerandGalileithinkhewasafraid,notof theinquisiPon,butofbeingridiculed • IttookPme,however,beforehismodelwasadopted • Itmadeabigsplashbutwasconsideredjustanother model • Copernicushadonlymade21observaPonsinhis wholelifeandofverypoorquality • HismodelofaSuncenteredsystemwasposiPvely beggingforbelerdata • AndtherewasaDanetoprovideit Tycho Brahe (1546 – 1601) DanishNoblemanwhogot interestedinAstronomywhen observingapredictedsolar eclipsein1560 HestudiedinmanyEuropean UniversiPesincludingRostock wherehelosthisnoseina dueltudiedinPolandand Aherreturninghomehewentto theislandofVen,builtacastleand twogiganPcobservatories(the VLTofitsday)andstarted observingstarsandplanets.He discoveredtheSupernovain1572 wasNOTan atmosphericphenomenon He became world famous and made an adjustment to Copernicus model Tycho Brahe (1546 – 1601) Johannes Kepler (1571 – 1630) Born in Germany. Also Inspired by astronomical phenomenon (comet of 1577) and eclipses of the Moon Studied Religion, mathematics, astronomy and astrology but was to argumentative to be a priest so he got the job as “Mathematicus” in Graz, developed a model of the Solar System/Universe based on hocus pocus of the Greek 5 solid figures He wrote about science and started an exchange of ideas with Brahe and Galileo Johannes Kepler (1571 – 1630) Born in Germany. Also Inspired by astronomical phenomenon (comet of 1577) and eclipses of the Moon Studied Religion, mathematics, astronomy and astrology but was to argumentative to be a priest so he got the job as “Mathematicus” in Graz, developed a model of the Solar System/Universe based on hocus pocus of the Greek 5 solid figures He wrote about science and started an exchange of ideas with Brahe and Galileo AherjoiningBrahewhohadmovedtoPrague,hereplacedhimas imperialastronomer/mathemaPcianatBrahe’sdeathin1601 Kepler now becomes the first modern astronomer. He uses Brahes exquisite observations to formulate the Keplerian laws 1. The orbit of the planets are ellipses with the Sun in one focus 2. As a planet moves around the Sun its radius vector sweep out equal areas in equal time 3. The square of the orbital period equals the cube of the distance of the planet to the Sun Galileos physical laws of motion is the final weapon overturning Aristotele and Ptolemaios. His observations of Venus phases, the Jupiter moons, as well as sunspots and lunar craters makes way for Isaac Newton and the modern times have arrived. He found that the stars are at great distances Now,slowlybutcertainlyenlightenmentbringsback“Astrobiology” AlreadyKeplerwritesascienceficPonnovelaboutatriptothe Moon WilliamHerschel(1738-1822)claimedthattheplanetswere inhabited AndPercivalLowelltogetherwithmanyotherstowardstheendof the19:thcenturywereconvincedthatMarswasinhabited Lowellgoeswildwithastrobiology FromhisprivateobservatoryinFlaggstaffArizonaheobserves Mars... Hediscoversanextensivenetworkofcanalsacrossthesurfaceand interpretthisas.... Theengineeringtriumphbyanancientracecarryingwaterfrom thepolesofadyingworldtowardstheequatorregions ButhehadatoocreaPveeyesight....Whathesawwasthisè The period of enlightenment is a period of great freedom of thought and the strong leadership of the churches is weakening. Revolution takes place in many countries At the same time we find the concept of the central place of mankind as well as the earth is diminishing. The Sun is an ordinary star, in an ordinary system of stars with an ordinary group of planets orbiting it. This must mean that we are also ordinary as life and that the Universe must be full of life But is this proven by anything we have said? And why did one change from the “Earth centric” to “the Earth is just a common grain of dust in an infinitely large Universe” Astrobiology turns into a science. Astrobiology • Whatisastrobiology? – Astrobiologyisthestudyoftheorigin,evoluPon, distribuPonandfutureoflifeinthewholeUniverse • Howcanitbeaddressed? – BystudytheeventsontheEarth,bysearchingforsignsof lifeontheplanetsintheSolarSystem,bysearchinginthe restoftheUniverse – Byusingacrossdisciplinarymethodincludingeverything fromgeophysicstoSETI – AstrobiologyaddressesahostofquesPons.Some examples: FormulaPonofAstrobiologicalQuesPons • TheEarth – BaselineforunderstandingtheoriginandevoluPonoflife – HowistheEarthchangingwithPmenowandinthefuture? • TheSun – OriginandevoluPonoftheSun – HowdoestheSun’sfluxvarywithPme – WhataretheimpactsonlifeontheEarthandtheSolarSystem • TheSolarsystem – Howdidthesun'sfamilyofplanetsandminorbodiesoriginate? – Howdidthesolarsystemevolvetoitscurrentdiversestate? – HowdidlifebeginandevolveonEarth,andhasitevolvedelsewhere intheSolarSystem? – WhatarethecharacterisPcsoftheSolarSystemthatleadtothe originsoflife? TheEarth’sclimate • Earth’sclimatehasbeenconstantlychanging essenPallysincethebeginning! – E.g.TheEarthhasexperiencednumerousice-agesinterspersedwith warmperiodsinthelastmillionyears – E.gTheEarthexperiencedasignificantwarmerclimateduringmostof Trias,JuraandtheCretaceous(maybe+10to15degCelcius) • TodaythetemperatureoftheEarthiswarmingup again – 0.6degCinlastcentury – Thiscouldbefasterthaneverbefore – Humansappeartobethereason TheEarth’sclimate • TheEarthmayhavebeencompletelyfrozen–manyPmes – 650MyrsagoasevidencedbyglacialdepositsattropicallaPtudes – PaleomagnePsmèwherelandmasseswere~650Myrsago – Neoproterozoic(1Gyrto541Myr)lowlaPtudelayersindicateglacial deposits – Openseadeposits(depthsof5-6000m) – BandedIronFormaPons(BIF:formonlyonanoxicoceans) • Triggermechanism:SomethingdeplePngthegreenhouse gasesintheEarth’satmosphere • ThiscoolstheEarthandincreasesthereflecPonofSunlight intospace • TheglaciaPonsmayhaveclearedthewayforthenextstep During the Neoproterozoic the Earth’s rotation rate decreased and day = 22h, the Sun’s luminosity went from 94% to 95% of today Most dramatic events: two great glaciations—the Sturtian at 720 Myrs and the Marinoan at 635 Myrs Metazoan life (multi-cell, specified organs, internal cavities) arise at end of Neoproterozoic è Cambrian Explosion 541 Myrs ago Metazoan life (multi-cell, specified organs, internal cavities) arise at end of Neoproterozoic è Cambrian Explosion 541 Myrs ago The "Cambrian explosion" consist of two phases of metazoan expansion into empty niches: first, an unprecedented rise in diversity as animals explored niches on the bottom of the sea, a second expansion in the early Cambrian as metazoan life becomes established in the water column The rate of diversification seen in the Cambrian phase of the explosion is unparalleled among marine animals Cambrian explosion, about 541 million years ago. Animals are divided into various sub-groups, some of which are: vertebrates (birds, mammals, amphibians, reptiles, fish); molluscs (clams, oysters, octopuses, squid, snails); arthropods (millipedes, centipedes, insects, spiders, scorpions, crabs, lobsters, shrimp); annelids (earthworms, leeches); sponges; and jellyfish. LifebeyondtheEarth? • WedonotknowwhenorhowlifearoseonEarth • WeknowverylilleabouttheevoluPonoflifeforthe first~4Gyrs • Wedonotknowwhyaher~4Gyrwehadthe “CambrianExplosion” ModernScience • Astrobiologymustconformtotheprinciplesof modernscience • Thestoryhowwewentfrompurephilosophyto modernscienceduring2000yearsshouldbeour lesson • WemustbecarefulwithspeculaPonandonlyletus beguidedbyspeculaPon–CarefullystaPngwhatis knowledgeandwhatisspeculaPon Make observation Ask a question Suggest a hypotheses Make a prediction Test prediction Test does not support hypotheses è Revise hypoteses Test supports hypotheses è Make additional predictions, test Hallmarksofscience Progressesthrough creaPonandtesPngof modelsthatexplain observaPons(as simplyaspossible) SeekexplanaPonsthat relyonlyonnatural causes Science Makestestable predicPonsabout naturalphenomena.If predicPonsdoesnot testoutmodelmustbe revisedorabandoned Occamsrazor IfscienPstshadonlyevaluatedCopernicusmodelquanPtaPvelythey shouldhavediscardedit InsteaditwasnotedthatitexplainedthingsliketheretrogrademoPon whichappealedtoscienPstsunPlKeplerfixeduptheinputdataofthe observaPons ScienPstscouldhavemadeamodelwithepicyclesthatfitCopernicus databutitwouldhavebeenextremelycomplex WilliamofOccam(1285–1349)formulatedtheideathatscienPsts shouldprefer(first)thesimpleroftwomodels.Thisiscalled“Occams razor” VerifiableObservaPons • WhatisacorrectobservaPon? • Mostwitnessesarealoneinobservinganevent–yetitworks incourt! • Ontheotherhand,literallythousandsofpeoplehaveseen flyingsaucersandotherUFO’s • NeitherisascienPficobservaPonunlessitisverifiable • ToparaphraseSpiderman“Extraordinarystatementsneed extraordinaryevidence • AscienPficallyverifiableobservaPonfitsthebill Issuesofastrobiology • • • • • • Whatislife? Cellsandthechemistryoflife RNAandDNAlife Extremophiles–dotheytellussomething? Couldlifebeverydifferent? Howlikelyislifetoarise? Abriefhistoryoflife • AlllifeonEarthisprobablyrelatedandgoesbacktoa“first cell”~4Gyrsago • Theoldestfossilsareprobably(thestromatolites)simpleonecellularmicrobes(Cyanobacteria)agowithnonucleus(~3.5 Gyr).Procaryotes.DominatethePre-Cambrian(super-Eon) • 2Gyrscellswithanucleusevolved.Eucaryotes • MulPcellularlifeareknownfrom650–542Myrsago.The firstsignsarefossilisedtracksofwormlikelife • 542MyrCambrianexplosion(TheBurgessshalefossils) • Organismswithshellsand(exo-)skeletonsappear • FirstVertebrates(488-416MyragoOrdovicium),Jawlessfish Abriefhistoryoflife Firstplantsonlandnotlaterthan444-416Myrago(Silur) Firstfrogs416-359Myrago(Devon) Firstmammals251-200Myrago(Trias) Firstprimates(endofCretaceus)66Myrago SeparaPngfromourcousins(Chimpanzees)7-6Myrago HomoErectus~1Myr–143Kyrago HomoHeidelbergiensis,Neanderthalensis,Denisovans800Kyr –40Kyr • HomoSapiens200Kyr-..... • • • • • • • Lifeoritsbuildingblocksarrivingfromspace • TheMurchisonmeteoritefellindaylightoverMurchison,Victoria, Australiaon28/91969.Itwaswidelyobservedasafireball,breakinginto atleast3fragmentsasitwasobservedandanimpacttremorwasfelt • 100kgofmasswascollectedinfragmentsofupto7kgoveranareaof13 km2includingoneinsideabarn • Over15aminoacidsplusahostofotherorganiccomponentshavebeen idenPfied.AmountsaresimilartothosefoundintheMillerexperiment • Sofarnoorganiccompoundshavebeenretrievedfromacomet,but observaPonsofHalley’sandothercometshavedemonstratedthe presenceofcarboniccompoundssuchashydrogencyanideand formaldehyde.Alsoadenine,oneofthebasesinnucleicacids(likeDNA) wasseeninHalley • Injustafewweeks,ESAwillalempttolandalaboratoryonthecomet 67P/Churyumov–Gerasimenko TracesofearlylifeonEarth • WecannotreallyexpecttofindtracesofthefirstlifeonEarthsinceitwas verysimpleandprimiPveandourplanethavebeenre-cycled • EarlyevoluPonappear,however,tohaveproducedmicroorganismsthat usedSunlightgavetracesinthefossilrecordthatcanbefoundaher3Gyr. • CyanobacteriaformedveryearlyanddominatedtheEarthforatleast1 Gyr.TheyproducedfreeoxygenandthuschangedtheEarth’satmosphere • SomeresearchersclaimthatfossiltracesofStromatolitesexistthatare 3500millionyearsold.Thesearecoloniesofcyanobacteriawhichproduce mineralisedmatsthatsPllexist Fossilised stromatolite TracesofearlylifeonEarth • Evenolderlifeisindicatedinmetamorphicsedimentaryrocks (metamorphicmeanschangeofformandthechangeis causedbyveryhightemperaturesand/orpressure) • Nofossilsremainintheserocks • Butcarboncompoundsfoundintherocksdemonstratean isotopicalraPo(C12/C13)thatindicateCarbonbeingingested fromtheatmospherethroughphotsyntheses.Agesashighas 4.4Gyrhavebeencalculated • OldironorescontainlayersofironoxideindicaPnghighlevels ofoxygenintheoceansveryearlyinEarth’shistory Consequencesofanoxygenbasedatmosphere • TheoxygenproducPoncausedthestrongestchangeofthe condiPonsonEarth-ever • Cyanobacteriaproducedoxygenandcausedthedemiseof thebiosphereprevioustotheirevoluPon-possiblyeven themselves • ThechangefromCO2toO2inouratmospherediminishedthe greenhouseeffectandtheEarthbecamecooler–possibly evencausingaglobaliceage • Luckily,thiscoolingwas–inthelongterm–compensatedby theSun’sincreasingluminosity Consequencesofanoxygenbasedatmosphere • TheproducPonofO2andtheevoluPonofEarth’satmosphere wasNOTaccompaniedbyextremechangesinthelifeon Earth • WeknowthattherewassimplelifeonEarthforalmost2Gyr sincetheevoluPonofthecyanobacteria,butnocomplexlife • The500-600Myragoaveritableexplosionoflifeappearedon EarthinarelaPvelyshortPme(tensofMyr) • ThereasonforthesuddenradiaPon–calledtheCambrian explosionorradiaPon–isnotknown. Consequencesofanoxygenbasedatmosphere • Hypothesesincludeglobaliceages“snowballEarth”which clearedoutecologicalniches,thepossibilitythattheO2+UV èO3(orOzone)ontopoftheEarth’satmospherecreateda filteragainsttheharmfulX-rayandUV-radiaPonfromtheSun allowingthedevelopmentofcomplexlife • PriortotheCambrianexplosionmostorganismsweresimple, composedofindividualcellsoccasionallyorganizedinto colonies • ItisimportantinAstrobiologybecausefindingthecausemay tellussomethingaboutthePmescaleoftheevoluPonoflife Whatislife(Clausius,1865) • Clausiusformulatedthefirsttwolawsof thermodynamics • 1:TheenergyoftheUniverseisconstant • 2:Theentropy(degreeofdisorder)oftheUniverse tendstoamaximum • Boltzmanspeculated:“Thegeneralstruggleforthe existenceofanimatebeingsisnotastruggleforraw materials,norforenergy,butfornegaBveentropy, availablebythetransiPonofenergyfromthehot SuntothecoldEarth StanleyMiller’sexperiment • A.Oparin(1894-1980)suggestedin1920:Pesthatareducingatmosphere withHandhydrogenatedmoleculestogetherwithelectricdischargesand UvradiaPonèchemicalreacPonsimportantforthechemistryoflife. • HaroldUrey(1893-1981,Nobelprizein1934,discoveryofD)suggestedan experimenttohisstudentStanleyMiller(1930-2007)whichhecarriedout in1953 • Hecreatedreducingatmospheresinthelabandpassedelectricdischarges throughit • Aherafewdayshefoundsomeblackgoointhetestvessel: – AsparPcacidandButyricacid–nosurprisesthere. – Thesecondmostcommonsubstance,however,wasglycinthesimplestaminoacid – Andnumber4wasalaninanotherimportantaminoacid+somemoreaminoacidsin significantamounts And amino acids are the building blocks of proteins! è Biochemestry! StanleyMiller’sexperiment • ProblemisofcoursethatwealreadyfoundthattheEarthwouldloseitsH, H2andrapidlygetanatmosphereofN2andCO2whichdoesnotallowthe resultsofMiller’sexperiment • MillerconPnuedtoworkfortherestofhislifeandotherideashavebeen tested: – MethaneejectedfromvolcanosintoaCO2richatmospheregivessomeaminoacidsbut notinsuchgreatamounts – ModerncalculaPonsindicatethattheEarthwouldhavebeenlosingitsHmuchslower thanpreviouslysuggestedèLifecouldhavehadPmetostart • Areducingatmosphereandcoldseas/oceansseemtobeastarPngpoint forcreaPnganenvironmentintowhichthebuildingblocksoflifecould havebeenformed.AlotofCH4isalsorequiredplussuitableenergy sources • ComparedtootheralternaPvesincludingthepresentEarth,these condiPonscouldbesearchedforaroundexoplanetswithadvanced instrumentsanditwouldhelpiftheplanetwaslargerthantheEarth (moreHandH2isretained)èSuperEarth Whatislife Schrödinger’sparadox(1944) • Inaworldgovernedbythe2ndlawofthermodynamics isolatedsystemsareexpectedtotendtoastateofmaximum disorder. • Lifeapproachesandmaintainsahighlyorderedstate–does thisviolatethe2ndLaw.Aparadox? • Lifeisnotanisolatedsystemènoparadox.Whynot? • Theincreaseoforderinsideanorganismiscompensated morethanenoughbytheincreaseindisorderoutsidethis organism.Thehighlyorderedstate,issustainedbycausinga netincreaseindisorderintheUniverse. • ThecomplexityonEarthcausedbyliferequiresenergymostly providedbytheSunandsupernova(radioacPvity)è increasesentropymorethanlifediminishit Whatislife Schrödinger’sparadox(1944) • SoweliveincloseconnecPonwiththeUniverseandnot separatefromitinanyway • Laterwewillseethisagainwhendiscussingphotosyntheses andhowthisconnectlifeonEarthwiththeSun • IstheUniverseintendedforlife?Thisisabigissuein Cosmology • ParallelUniverseswithdifferentnaturallaws(aninfinite amountsolvethisissue Biochemistry,moleculargenePcsand metabolism • MoleculesbuildinguplifeonEarthconsistofC boundtootherCatomswithcovalentbonds • AcovalentbondisachemicalbondconsisPngof sharedelectronpairsbetweenatoms • BondsareformedbetweenC=CandwithH,OandN Biochemistry,moleculargenePcsand metabolism Covalentbonds Waterisauniquemolecule • ThebindingsbetweenHandOrestronglypolarized • TheanglesbetweenHandOformadipolèH2Ocanform weakchemicalbondswithchargeddissolvedmoleculesand inorganicionsçèwaterisaverygoodsolvent • ThebondsbetweenindividualH2Omoleculesgivewaterhigh melPngpoints,boilingpointsandsurfacetension • WatercanbeionizedintoH3O+andOH-(oxoniumand hydroxyl)andbehaveaseitheranacidorabaseandhigh electricconducPvity • LifeisprobablynotpossiblewithoutH2ObutalternaPves suggestedinclude: – Ammonia,NH3 – Formamide,CH3NO Waterisauniquemolecule Ammonia Formamide LifebasedonAmmonia,NH3andFormamide,CH3NO wouldbeverydifferentandhaveacompletely differentbiochemistry LifeasweknowitisbasedonCarbon • CarbonhasthepropertythatwithH,O,Nitcanform anenormousamountofdifferentandbothsimple andcomplexmolecules–organicmolecules • Secondly,smallerorganicmolecules(nucleoPdes, aminoacidsandmonosaccharides=simplesugars) havethepropertythattheycanformlongchains • ExcepBonsareCO2andcarbonatemineralswhicharenot considertobeorganic • E.g.DeoxiribonNucleidAcid(DNA),RiboNucleidAcid (RNA),proteinsandcarbohydrates LifeasweknowitisbasedonCarbon DNA