{"id":28708,"date":"2018-08-28T06:00:21","date_gmt":"2018-08-28T03:00:21","guid":{"rendered":"https:\/\/bilimvegelecek.com.tr\/?p=28708"},"modified":"2018-11-18T14:11:46","modified_gmt":"2018-11-18T11:11:46","slug":"dunyada-yasam-ne-zaman-ve-nerede-basladi","status":"publish","type":"post","link":"https:\/\/bilimvegelecek.com.tr\/index.php\/2018\/08\/28\/dunyada-yasam-ne-zaman-ve-nerede-basladi","title":{"rendered":"D\u00fcnyada ya\u015fam ne zaman ve nerede ba\u015flad\u0131?"},"content":{"rendered":"

G\u00fcn\u00fcm\u00fczde ya\u015fayan canl\u0131lar\u0131n nas\u0131l bir evrim s\u00fcreciyle bug\u00fcnk\u00fc hallerini ald\u0131klar\u0131 \u00e7ok uzun zamand\u0131r bilim insanlar\u0131n\u0131n tart\u0131\u015fma konusudur. Canl\u0131lar\u0131n evrimi Evrim Kuram\u0131 ve genetik ara\u015ft\u0131rmalar sayesinde art\u0131k b\u00fcy\u00fck oranda a\u015fama kat edilmi\u015f olan bir tart\u0131\u015fmad\u0131r. Buna g\u00f6re canl\u0131lar\u0131n milyarlarca y\u0131l boyunca basitten karma\u015f\u0131\u011fa evrimle\u015fti\u011fini art\u0131k biliyoruz.<\/p>\n

Peki her \u015feyin ba\u015flang\u0131c\u0131 nas\u0131l oldu? D\u00fcnyada ilk canl\u0131 ya\u015fam\u0131 ne zaman ve nerede ba\u015flad\u0131? Deniz \u015eahin, Bilim ve Gelecek Kitapl\u0131\u011f\u0131\u2019ndan \u00e7\u0131kan 50 Soruda Ya\u015fam\u0131n Tarihi<\/em><\/a> ba\u015fl\u0131kl\u0131 kitapta bu sorular\u0131 \u015f\u00f6yle yan\u0131tl\u0131yor: (1)<\/p>\n

\u201cD\u00fcnyada ya\u015fam ne zaman ba\u015flam\u0131\u015ft\u0131r?<\/strong>
\n\u201cElde edilen en eski fosil kaynaklar\u0131, ya\u015fam\u0131n d\u00fcnya \u00fczerinde milyarlarca y\u0131ld\u0131r var oldu\u011funu g\u00f6steriyor. G\u00fcney Afrika ve Avustralya\u2019da bulunan ve \u201cstromatolit\u201d ad\u0131 verilen tarih\u00f6ncesi fosil kayalar, \u00f6nemli mikro fosil kaynaklar\u0131d\u0131r. (\u015eekil 1) Mikroorganizmalar\u0131n \u00fcst \u00fcste katmanlar halinde birikmesi ile olu\u015fan bu kayalardaki fosil \u00f6rnekleri, ya\u015fam\u0131n g\u00fcn\u00fcm\u00fczden en az 3,5 milyar y\u0131l \u00f6nce var oldu\u011funu g\u00f6steriyor. Kayalar \u00fczerinde, \u00f6zellikle siyanobakterilerin (mavi-ye\u015fil alg olarak da bilinir) atalar\u0131 oldu\u011fu d\u00fc\u015f\u00fcn\u00fclen h\u00fccre fosilleri yo\u011fun olarak bulunuyor.<\/p>\n

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\u015eekil 1:<\/strong> Stromatolitler, tekh\u00fccreli organizmalar taraf\u0131ndan tabakalar halinde olu\u015fturulan kayalard\u0131r. D\u00fcnya \u00fczerinde ya\u015fam\u0131\u015f en eski canl\u0131 fosilleri bu kayalar \u00fczerinde bulunmu\u015ftur.<\/figcaption><\/figure>\n

\u201cYine bu d\u00f6nemden kalma kayalarda yap\u0131lan incelemelerde 3,8 milyar y\u0131ll\u0131k biyolojik karbon \u00f6rneklerinin bulunmas\u0131 da, canl\u0131l\u0131\u011f\u0131n ilk ortaya \u00e7\u0131k\u0131\u015f\u0131n\u0131n bu d\u00f6neme kadar geriye gidebilece\u011fi anlam\u0131na geliyor.<\/p>\n

\u201cYa\u015fam\u0131n nas\u0131l ba\u015flad\u0131\u011f\u0131n\u0131n \u00e7\u00f6z\u00fclmesi hem heyecanl\u0131 hem de meydan okuma gerektiren bilimsel bir problemdir. \u015eimdiye kadar 3,5 milyar y\u0131ldan eski fosil \u00f6rne\u011fi bulunamam\u0131\u015ft\u0131r. D\u00fcnya\u2019n\u0131n ilk zamanlar\u0131ndaki kimyasal ve fiziksel \u015fartlar\u0131n\u0131 bilmedi\u011fimizden, ilk organizmalar\u0131n olu\u015ftu\u011fu ortam ko\u015fullar\u0131n\u0131n tekrar yarat\u0131lmas\u0131 zordur. Yine de, ara\u015ft\u0131rmac\u0131lar kendili\u011finden \u00e7o\u011falan organizmalar\u0131n nas\u0131l olu\u015ftu\u011funu ve evrimle\u015fmeye ba\u015flad\u0131\u011f\u0131n\u0131 anlamak \u00fczere hipotezler kurmu\u015flar ve bu hipotezlerin olas\u0131l\u0131\u011f\u0131n\u0131 laboratuvar \u015fartlar\u0131nda test etmi\u015flerdir. Bu hipotezlerin hi\u00e7biri \u00fczerinde genel ortak bir uzla\u015fmaya var\u0131lmam\u0131\u015fsa da, bu t\u00fcr temel sorular\u0131n \u00e7\u00f6z\u00fcm\u00fcnde ilerlemeler kaydedilmi\u015ftir.<\/p>\n

\u201cYa\u015fam nerede ba\u015flad\u0131?<\/strong>
\n\u201cYayg\u0131n olan bilimsel g\u00f6r\u00fc\u015fe g\u00f6re ya\u015fam, ilk D\u00fcnya\u2019n\u0131n oksijen ya da oksitleyici di\u011fer gazlar bulunmayan indirgen ortam\u0131nda olu\u015fmu\u015ftu. \u0130norganik molek\u00fcllerden organik molek\u00fcller olu\u015ftu ve birikti. Karma\u015f\u0131k yap\u0131daki biyomolek\u00fcller de, bu organik molek\u00fcllerden olu\u015ftu.<\/p>\n

\u201c\u0130lk h\u00fccrelerin b\u00fcy\u00fck olas\u0131l\u0131kla fermentatif heterotroflar (2) oldu\u011fu d\u00fc\u015f\u00fcn\u00fcl\u00fcyor. Hen\u00fcz oksijenli solunum ya da fotosentez geli\u015fmemi\u015fti ve gerekli enerji ortamda bulunan enerji kaynaklar\u0131ndan sa\u011flan\u0131yordu.<\/p>\n

\u201cYa\u015fam\u0131n d\u00fcnya \u00fczerinde nerede ortaya \u00e7\u0131kt\u0131\u011f\u0131 sorusu kesin olarak cevapland\u0131r\u0131lamasa da, farkl\u0131 hipotezlerde \u00f6ne \u00e7\u0131kan yerler aras\u0131nda okyanus diplerindeki hidrotermal bacalar\u0131n \u00e7evreleri ya da volkanlar\u0131n \u00e7evrelerindeki ufak su birikintileri bulunuyor. Yayg\u0131n olarak kabul edilen fikir ise, ya\u015fam\u0131n sularda ortaya \u00e7\u0131kt\u0131\u011f\u0131d\u0131r. Bunun nedeni ise, ilkel D\u00fcnya atmosferinde hen\u00fcz ozon tabakas\u0131 bulunmad\u0131\u011f\u0131ndan, G\u00fcne\u015f\u2019ten gelen y\u00fcksek enerjili \u0131\u015f\u0131nlar\u0131n canl\u0131l\u0131\u011f\u0131n atmosferde olu\u015fmas\u0131n\u0131 b\u00fcy\u00fck ihtimalle engelleyecek olu\u015fudur.<\/p>\n

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\u015eekil 2:<\/strong> Okyanus diplerindeki hidrotermal bacalar canl\u0131lar i\u00e7in enerji ve zengin mineral kayna\u011f\u0131d\u0131r.<\/figcaption><\/figure>\n

\u201c\u015eimdi \u00f6nde gelen hipotezlerden okyanus diplerindeki hidrotermal bacalara g\u00f6z atal\u0131m. Bu bacalarda kimyasallar\u0131n bollu\u011fu ve sa\u011flad\u0131\u011f\u0131 enerji, ilk canl\u0131l\u0131\u011f\u0131n ba\u015flamas\u0131 i\u00e7in uygun ortam olu\u015fturmu\u015f olabilir. (\u015eekil 2) Deniz suyu, okyanus dibindeki \u00e7atlaklardan diplere do\u011fru s\u0131zar ve alt tabaka olan manto tabakas\u0131n\u0131n s\u0131cakl\u0131\u011f\u0131yla \u0131s\u0131t\u0131larak tekrar yukar\u0131 \u00e7\u0131kar. Deniz taban\u0131ndan \u00e7\u0131kan su, \u00e7ok s\u0131cak (400 \u00b0C) ve mineral bak\u0131m\u0131ndan olduk\u00e7a zengindir. \u00d6zellikle demir ve s\u00fclf\u00fcr daha s\u0131cak olan \u201csiyah duman bacalar\u0131ndan\u201d sal\u0131n\u0131rken; baryum, kalsiyum ve silikon ise s\u0131cakl\u0131\u011f\u0131 daha d\u00fc\u015f\u00fck olan \u201cbeyaz duman bacalar\u0131ndan\u201d sal\u0131n\u0131r. Bu suyun kaynamay\u0131\u015f\u0131n\u0131n nedeni, okyanus dibindeki y\u00fcksek bas\u0131n\u00e7t\u0131r. S\u0131cak su okyanus taban\u0131n\u0131n so\u011fuk suyu ile kar\u015f\u0131la\u015ft\u0131\u011f\u0131nda, mineraller \u00e7\u00f6kerek bu bacalar\u0131 olu\u015fturur. Suyun tam \u00e7\u0131k\u0131\u015f b\u00f6lgesi a\u015f\u0131r\u0131 s\u0131cak oldu\u011fu halde, \u00e7evresine do\u011fru daha \u0131l\u0131ml\u0131 s\u0131cakl\u0131k ku\u015faklar\u0131 olu\u015fturur. \u0130\u015fte bacan\u0131n s\u0131cak suyu ve okyanusun so\u011fuk suyu aras\u0131ndaki \u0131l\u0131man b\u00f6lgeler, enerji ve mineral a\u00e7\u0131s\u0131ndan zengin, ilk h\u00fccrelerin ortaya \u00e7\u0131kabilece\u011fi d\u00fc\u015f\u00fcn\u00fclen yerlerdir. \u0130lk defa 1977\u2019de ortaya \u00e7\u0131kar\u0131lan hidrotermal bacalar\u0131n Pasifik ve Atlantik Okyanuslar\u0131\u2019nda di\u011fer \u00f6rnekleri de bulunmu\u015ftur. Bacalar \u00e7evresinde, \u0131\u015f\u0131ks\u0131z ortamda, farkl\u0131 bakteri t\u00fcrlerinden dev boru kurt\u00e7u\u011funa, midyeden karidese kadar farkl\u0131 t\u00fcrler ya\u015famlar\u0131n\u0131 s\u00fcrd\u00fcrmektedir.\u201d<\/p>\n

Haftaya yeni bir soruyla yine birlikte olaca\u011f\u0131z. O zamana kadar ya\u015fam\u0131n ba\u015flang\u0131c\u0131na ili\u015fkin \u015fu e\u011flenceli animasyona (3) g\u00f6z atabilirsiniz:<\/p>\n