Question

Explain the sequences of events from the first living cell till the evolution of photosynthetic autotrophs.

Answer 1

1. The first cells were likely simple, anaerobic heterotrophs that obtained energy and organic material from their surroundings.
2. As resources became limited, some organisms evolved ways to obtain energy from inorganic substances; later, photosynthetic organisms arose.
3. The evolution of chlorophyll enabled organisms to use light energy to make organic food.
4. Photosynthetic organisms released oxygen as a by-product.
5. Oxygen accumulated, changing the atmosphere from reducing to oxidising; it also enabled the later development of aerobic respiration and contributed to ozone formation. 

Photosynthesis transformed both life’s energy pathways and Earth’s atmosphere.