The very lack of oxygen in the primordial atmosphere should, however, favour
light-driven chemical syntheses. Without the ozone shield, the solar light
reaching Earth contained a UV component that was 10–1000 times stronger
than it is today [133,134] and could have driven diverse chemical reactions, in
particular carbon fixation. The major constituents of the primordial atmosphere
(CO2, N2, CH4, and water vapour [25,93-100]) let UV rays with λ > 240 nm
through [133]. The fossils of phototropic communities, which apparently flourished
as far back as 3.4–3.5 Ga [25,135-139], also indicate that the primordial
atmosphere was transparent to solar light. Hence, no other known energy source
could compete with solar irradiation in terms of strength and access to the whole
of the Earth’s surface.
The very lack of oxygen in the primordial atmosphere should, however, favourlight-driven chemical syntheses. Without the ozone shield, the solar lightreaching Earth contained a UV component that was 10–1000 times strongerthan it is today [133,134] and could have driven diverse chemical reactions, inparticular carbon fixation. The major constituents of the primordial atmosphere(CO2, N2, CH4, and water vapour [25,93-100]) let UV rays with λ > 240 nmthrough [133]. The fossils of phototropic communities, which apparently flourishedas far back as 3.4–3.5 Ga [25,135-139], also indicate that the primordialatmosphere was transparent to solar light. Hence, no other known energy sourcecould compete with solar irradiation in terms of strength and access to the wholeof the Earth’s surface.
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