With so many things that needed to go right, and so many things that could have gone wrong, the very fact that you're reading this – in fact, your very existence – is the result of innumerable strokes of luck. Scientists have long sought an explanation as to why stable conditions on Earth have persisted long enough for life to evolve over millions of years. Now a team has hit upon two mechanisms, "sequential selection" and "selection by survival alone," as a possible solution to this "Gaia puzzle."

The Gaia hypothesis, (aka the Gaia theory or Gaia principle), is the idea, first proposed by James Lovelock in the 1970s, that the life-supporting conditions of our planet are maintained through a self-regulating synergistic system created by the interactions between living organisms and their inorganic surroundings. Scientists have wondered how, in the face of threats such as a brightening sun, volcanoes and meteor strikes, such a complex system might work to keep the planet in a prolonged state in which life can evolve.

According to a team led by researchers at the University of Exeter, the answer could lie with what's known as "sequential selection." In this form of global environmental regulation, life or systems that destabilize the environment tend not to last long and result in extinctions and further change until a stable state emerges that tends to persist. This stability, in turn, gives the system more time to acquire additional persistence-enhancing traits – a process called "selection by survival alone."

"We can now explain how the Earth has accumulated stabilizing mechanisms over the past 3.5 billion years of life on the planet," says Professor Tim Lenton, from the University of Exeter. "The central problem with the original Gaia hypothesis was that evolution via natural selection cannot explain how the whole planet came to have stabilizing properties over geologic timescales. Instead, we show that at least two simpler mechanisms work together to give our planet with life self-stabilizing properties."

Dr James Dyke, from the University of Southampton, who contributed to the research, added, "As well as being important for helping to estimate the probability of complex life elsewhere in the universe, the mechanisms we identify may prove crucial in understanding how our home planet may respond to drivers such as human-produced climate change and extinction events."

The team's paper appears in the journal Trends in Ecology and Evolution.