Earth formed about 4.5 billion years ago. Life followed around 3.8 billion years ago, apparently almost as soon as the first rocks solidified from the molten surface. However, the ancestors of all modern complex animals — insects, crustaceans, vertebrates of all descriptions — didn’t arrive on the scene until about 570 million years ago, in what is commonly known as the “Cambrian explosion”. Today we know it wasn’t quite as sudden an event as we used to think, but it was still relatively rapid in geologic and evolutionary terms.

But what took critters so long? A new paper proposes that the culprit may have been lack of oxygen in the air and water, based on a study of oxidation: the way oxygen bonds strongly with many other types of atoms. My latest article in The Daily Beast has the story:

The answer may be that animals are greedy: they need a lot of oxygen to grow big and complicated. Early Earth didn’t have much oxygen, but microbes changed the chemical content of the atmosphere over time from something alien and poisonous to us into the breathable air we have today. A new paper showed that the oxygen level as recently as 800 million years ago was only a tiny fraction of today’s—far too low to support oxygen-breathers like our ancestors and their relatives. [Read more…]