Sophie's World

by Jostein Gaarder

First of all, our planet was quite different from the way it looks today. Since there was no life, there was no oxygen in the atmosphere. Free oxygen was first formed by the photosynthesis of plants. And the fact that there was no oxygen is important. It is unlikely that life cells – which, again, can form DNA – could have arisen in an atmosphere containing oxygen.’ ‘Why?’ ‘Because oxygen is strongly reactive. Long before complex molecules like DNA could be formed, the DNA molecular cells would be oxidized.’ ‘Really.’ ‘That is how we know for certain that no new life arises today, not even so much as a bacterium or a virus. All life on earth must be exactly the same age. An elephant has just as long a family tree as the smallest bacterium. You could almost say that an elephant – or a human being – is in reality a single coherent colony of monocellular creatures.