Toxic gases and mass extinctions mean Earth isn’t always life friendly (Image: Sarah Howell)

Interactive graphic: Medean extinctions throughout evolutionary history

THE twin Viking landers that defied the odds to land on Mars in 1976 and 1977 had one primary goal: to find life. To the disappointment of nearly all concerned, the data they sent back was a sharp dash of cold water. The Martian surface was harsh and antibiotic and there was no sign of life.

To two NASA scientists, James Lovelock and Dian Hitchcock, this came as no surprise – in fact, they would have been amazed to see any evidence of life on Mars. A decade before Viking, Lovelock and Hitchcock, both atmospheric scientists, had used observations of the Martian atmosphere to deduce that there could be no life on the planet.

From their research arose one of the most influential, ground-breaking scientific ideas of the 20th century – the Gaia hypothesis, named after the ancient Greek goddess of the Earth, a nurturing “mother” of life. But is it correct? New scientific findings suggest that the nature of life on Earth is not at all like Gaia. If we were to choose a mythical mother figure to characterise the biosphere, it would more accurately be Medea, the murderous wife of Jason of the Argonauts. She was a sorceress, a princess – and a killer of her own children.

The Gaia story starts in the 1960s, when Lovelock and Hitchcock showed that the Martian atmosphere was in a state of chemical equilibrium – a stagnant pool of carbon dioxide with a dash of nitrogen but very little oxygen, methane or hydrogen. …