科學(xué)家提出,，在海洋表面的光合細(xì)菌可能在地球早期“單調(diào)的數(shù)十億年”里妨礙了多細(xì)胞生物的形成，當(dāng)時海洋的大部分處于大致無氧的狀態(tài),。
David Johnston及其同事提出，這種細(xì)菌很可能在地球的18億年前到8億年前的中年時期使用硫阻止了海洋和空氣中的氧的大量積累,。這組作者提出,，這些細(xì)菌在那個時期占據(jù)了海洋表面，產(chǎn)生了一個無氧區(qū)域,，在那里，使用硫的細(xì)菌傳播開來,，在全世界創(chuàng)造出了具有化學(xué)毒性的海洋層,。這些細(xì)菌主要使用硫化物而不是水從而獲取能量。否則硫化物會與鐵結(jié)合形成黃鐵礦（愚人金）,。在地質(zhì)時代的尺度上,，在海洋中循環(huán)的黃鐵礦降低了硫的濃度，這限制了這種細(xì)菌的能量來源,，因此也就讓海洋和大氣無氧,。最終這種循環(huán)被打破了，把更多的鐵和氧從海洋中解放出來,。
這組作者說,，制氧的光合細(xì)菌最終占據(jù)了海洋，這間接導(dǎo)致了多細(xì)胞生物的形成——最初是在海洋中,，隨后出現(xiàn)在陸地上,。（生物谷bioon.com）
生物谷推薦原始出處：
PNAS September 28, 2009, doi: 10.1073/pnas.0909248106
Anoxygenic photosynthesis modulated Proterozoic oxygen and sustained Earth's middle age
D. T. Johnstona,b,1,2, F. Wolfe-Simona,1,2, A. Pearsona,2 and A. H. Knollb,2
aDepartment of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA, 02138; and
bDepartment of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138
Molecular oxygen (O2) began to accumulate in the atmosphere and surface ocean ca. 2,400 million years ago (Ma), but the persistent oxygenation of water masses throughout the oceans developed much later, perhaps beginning as recently as 580–550 Ma. For much of the intervening interval, moderately oxic surface waters lay above an oxygen minimum zone (OMZ) that tended toward euxinia (anoxic and sulfidic). Here we illustrate how contributions to primary production by anoxygenic photoautotrophs (including physiologically versatile cyanobacteria) influenced biogeochemical cycling during Earth's middle age, helping to perpetuate our planet's intermediate redox state by tempering O2 production. Specifically, the ability to generate organic matter (OM) using sulfide as an electron donor enabled a positive biogeochemical feedback that sustained euxinia in the OMZ. On a geologic time scale, pyrite precipitation and burial governed a second feedback that moderated sulfide availability and water column oxygenation. Thus, we argue that the proportional contribution of anoxygenic photosynthesis to overall primary production would have influenced oceanic redox and the Proterozoic O2 budget. Later Neoproterozoic collapse of widespread euxinia and a concomitant return to ferruginous (anoxic and Fe2+ rich) subsurface waters set in motion Earth's transition from its prokaryote-dominated middle age, removing a physiological barrier to eukaryotic diversification (sulfide) and establishing, for the first time in Earth's history, complete dominance of oxygenic photosynthesis in the oceans. This paved the way for the further oxygenation of the oceans and atmosphere and, ultimately, the evolution of complex multicellular organisms.
