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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 ...
Such archaeal photosynthesis might have been the earliest form of photosynthesis that evolved on Earth, as far back as the Paleoarchean, preceding that of cyanobacteria (see Purple Earth hypothesis). While the details may differ between species , the process always begins when light energy is absorbed by the reaction centers , proteins that ...
At long irregular intervals, Earth's biosphere suffers a catastrophic die-off, a mass extinction, [9] often comprising an accumulation of smaller extinction events over a relatively brief period. [10] The first known mass extinction was the Great Oxidation Event 2.4 billion years ago, which killed most of the planet's obligate anaerobes.
The history of life on Earth traces the processes by which living and extinct organisms evolved, from the earliest emergence of life to the present day. Earth formed about 4.5 billion years ago (abbreviated as Ga, for gigaannum) and evidence suggests that life emerged prior to 3.7 Ga. [1] [2] [3] The similarities among all known present-day species indicate that they have diverged through the ...
These are flattened sacs called thylakoids where photosynthesis is performed. [ 14 ] [ 15 ] Photoautotrophic eukaryotes such as red algae , green algae and plants perform photosynthesis in chlorophyllic organelles that are thought to have their ancestry in cyanobacteria, acquired long ago via endosymbiosis.
A global glaciation event called Snowball Earth, from around 720-635 mya in the Cryogenian period, is believed to have been at least partially caused by early photosynthetic organisms, which reduced the concentration of carbon dioxide and decreased the greenhouse effect in the atmosphere, [24] leading to an icehouse climate.
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".