14:20 〜 14:40
[MIS08-03] Green Sea Hypothesis: Coevolution of Earth Surface and Cyanobacteria
★Invited Papers
キーワード：地球と生命の共進化、シアノバクテリア、太古代、光集光アンテナ
Carl Sagan described Earth as a “pale blue dot,” as seen by Voyager 1 from 6 billion kilometers away. This blue hue results from Rayleigh scattering of sunlight in the atmosphere combined with the reflection from the oceans, symbolizing Earth as the cradle of life. But does a blue hue alone indicate a planet’s potential to support life?
Over 4.5 billion years, Earth’s surface has been reshaped by both geological forces and life. Cyanobacteria—the first oxygenic photosynthetic organisms—used sunlight to split water, releasing oxygen and triggering the Great Oxidation Event (GOE) around 2.4 billion years ago. This pivotal event paved the way for aerobic life. Cyanobacteria capture light using large, complex phycobilisomes that channel energy to photosystems I and II. Although all phototrophs rely on chlorophyll, cyanobacteria also employ additional pigments called phycobilins to absorb wavelengths that complement chlorophyll. This raises an intriguing question: why did cyanobacteria evolve phycobilisomes?
Here, we propose the "Green Sea Hypothesis," which describes the co-evolutionary relationship between oxygenic phototrophs and light environments that defined the aquatic landscape of the Archaean Earth. We hypothesize that during the Archean era, the underwater light spectrum was predominantly green due to the precipitation of oxidized iron (Fe(III)). In this green-light environment, the evolution of photosynthesis may have been driven by the need to harness green light. Our hypothesis is supported by experiments simulating Darwinian evolution and molecular phylogenetic analyses. This hypothesis also indicates that a green color may serve as a marker of a distinct evolutionary stage on inhabited planets.
In this presentation, we discuss the Green Sea Hypothesis from an astrobiological perspective.
Over 4.5 billion years, Earth’s surface has been reshaped by both geological forces and life. Cyanobacteria—the first oxygenic photosynthetic organisms—used sunlight to split water, releasing oxygen and triggering the Great Oxidation Event (GOE) around 2.4 billion years ago. This pivotal event paved the way for aerobic life. Cyanobacteria capture light using large, complex phycobilisomes that channel energy to photosystems I and II. Although all phototrophs rely on chlorophyll, cyanobacteria also employ additional pigments called phycobilins to absorb wavelengths that complement chlorophyll. This raises an intriguing question: why did cyanobacteria evolve phycobilisomes?
Here, we propose the "Green Sea Hypothesis," which describes the co-evolutionary relationship between oxygenic phototrophs and light environments that defined the aquatic landscape of the Archaean Earth. We hypothesize that during the Archean era, the underwater light spectrum was predominantly green due to the precipitation of oxidized iron (Fe(III)). In this green-light environment, the evolution of photosynthesis may have been driven by the need to harness green light. Our hypothesis is supported by experiments simulating Darwinian evolution and molecular phylogenetic analyses. This hypothesis also indicates that a green color may serve as a marker of a distinct evolutionary stage on inhabited planets.
In this presentation, we discuss the Green Sea Hypothesis from an astrobiological perspective.