Viewpoint: Yes, morphological analyses and laser-Raman imaging have shown that photosynthetic life on Earth existed 3.5 billion years ago.

Viewpoint: No, it is more likely that life at the time was still using other, chemical, forms of energy to survive.

The two essays that follow debate claims concerning the possible early appearance of photosynthesis, which some scientists maintain originated on Earth 3.5 billion years ago (Gya). If this is true, it would be extraordinary, because Earth at that time was quite different from now, and indeed had only recently cooled after millions of years of battering by asteroids. For photosynthesis to have taken place at that time—and there is considerable evidence to suggest that it did—would be extremely remarkable, given the complexity of the photosynthetic process and the level of evolutionary advancement...