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The first photosynthetic organisms probably evolved early in the evolutionary history of life and most likely used reducing agents such as hydrogen rather than water. [2] There are three major metabolic pathways by which photosynthesis is carried out: C 3 photosynthesis, C 4 photosynthesis, and CAM photosynthesis.
The Purple Earth Hypothesis (PEH) is an astrobiological hypothesis, first proposed by molecular biologist Shiladitya DasSarma in 2007, [1] that the earliest photosynthetic life forms of Early Earth were based on the simpler molecule retinal rather than the more complex porphyrin-based chlorophyll, making the surface biosphere appear purplish ...
Photosynthesis and cellular respiration are distinct processes, as they take place through different sequences of chemical reactions and in different cellular compartments (cellular respiration in mitochondria). [15] [16] The general equation for photosynthesis as first proposed by Cornelis van Niel is: [17]
The photosynthesis conducted by land plants and algae is the ultimate source of energy and organic material in nearly all ecosystems. Photosynthesis, at first by cyanobacteria and later by photosynthetic eukaryotes, radically changed the composition of the early Earth's anoxic atmosphere, which as a result is now 21% oxygen.
The Earth was formed at 4.54 Gya, and the earliest evidence of life on Earth dates from at least 3.8 Gya from Western Australia. Some studies have suggested that fossil micro-organisms may have lived within hydrothermal vent precipitates dated 3.77 to 4.28 Gya from Quebec , soon after ocean formation 4.4 Gya during the Hadean .
The first primary producers that used photosynthesis were oceanic cyanobacteria about 2.3 billion years ago. [ 20 ] [ 21 ] The release of molecular oxygen by cyanobacteria as a by-product of photosynthesis induced global changes in the Earth's environment.
The first autotrophic organisms likely evolved early in the Archean but proliferated across Earth's Great Oxidation Event with an increase to the rate of oxygenic photosynthesis by cyanobacteria. [8] Photoautotrophs evolved from heterotrophic bacteria by developing photosynthesis. The earliest photosynthetic bacteria used hydrogen sulphide.
These are the oldest known trees of the world's first forests. Prototaxites was the fruiting body of an enormous fungus that stood more than 8 meters tall. By the end of the Devonian, the first seed-forming plants had appeared. This rapid appearance of so many plant groups and growth forms has been called the "Devonian Explosion".