In the beginning, planet Earth was a very inhospitable place with no oxygen and only single-celled bacteria as inhabitants. According to a new study, the oxygen content in the air began to increase about 2.4 billion years ago, at the same time as the global glaciation and when all continents were gathered in a single huge landmass, or supercontinent. How to explain the exact connection between these events, however, is a question that baffles the researchers.