Our bodies rely on a biological clock that is immune to light or darkness, but controls how long we sleep in our oak beds and can give us jetlag. This clock is found in an enzyme called peroxiredoxin (PRX) and is common to almost all life, Akhilesh Reddy at the University of Cambridge has discovered alongside his colleagues. The fact that PRX has been found in mice, fruit flies, a plant, a fungus, an alga, bacteria, and even in archaea, which is the most primitive form of cellular life, implied that the enzyme has been around for 2.5 billion years. A gene sequence analysis carried out by the researchers backed this up, leading to PRX being dubbed a 'grandfather clock'. When PRX first came about, days only lasted 11 hours as the Earth spun faster. However, the enzyme has moved with the times. "It will have adapted to the lengthening of the day-night cycle over time," Reddy told New Scientist (May 16th). This clock is the only one found so far that is common to different groups of organisms. It helps them to survive, and keeps running on its own 24-hour cycle even if the organism is kept in constant light or constant darkness. This research has shown that our biological clocks are much older than it was previously believed, and that they may have evolved during the Great Oxygenation Event (GOE) when the oxygen released by photosynthesis began to gather in the atmosphere.