As time went on

There were as yet no predators. Some molecules reproduced themselves inefficiently, competed for building blocks and left crude copies of themselves. With reproduction, mutation and the selective elimination of the least efficient varieties, evolution was well under way, even at the molecular level. As time went on, they got better at reproducing. Molecules with specialized functions eventually joined together, making a kind of molecular collective the first cell. Plant cells today have tiny molecular factories, called chloroplasts, which are in charge of photosynthesis – the conversion of sunlight, water and carbon dioxide into carbohydrates and oxygen.