Conjectures and reveries.

Area of Science:

• Biochemistry
• Astrobiology
• Geochemistry

Background:

• The origin of photosynthesis is a critical question in understanding early life on Earth.
• Previous hypotheses suggest a role for inorganic compounds and self-replicating molecules.

Purpose of the Study:

• To propose a detailed evolutionary pathway for photosynthesis.
• To elucidate the sequential development of key molecular components and processes.

Main Methods:

• The study is theoretical, based on the chemical evolution of key molecules.
• It traces the incorporation of elements like iron, sulfur, nitrogen, and phosphate.
• It analyzes the evolution of chromophores and electron transport chains.

Main Results:

• Photosynthesis evolved in four distinct phases, starting with carbon dioxide photoreduction by ferrous ions.
• Sulfur and nitrogen incorporation led to complex organic molecules like chlorophyll.
• Chromophores evolved from ferrous ions to chlorophyll, suggesting a shift in light absorption from UV to red.

Conclusions:

• The proposed model outlines a plausible chemical and biological evolution of photosynthesis.
• This pathway highlights the stepwise development of essential components for light energy conversion.
• The evolution of chromophores indicates an adaptation to changing light environments over time.