Around the world, from Alaska to Indonesia, more than 200 ancient myths tell of a human civilisation brought to an end by flood and fire. Compelling scientific evidence, which began to emerge only in 2007, indicates that these stories, such as the tale of Noah and his Ark, are based on hard fact.

A cataclysm rocked our planet 12,800 years ago, causing mass extinctions of large animals such as the mammoth and sloth bears, and all but wiping out our own race. An entire episode in the human story was rubbed out, a chapter not of unsophisticated hunter-gatherers but of advanced technology.

All the signs are that remnants of this civilisation struggled on, sustained by a few individuals who knew the secrets of the former age. To their primitive contemporaries, it appeared that they possessed magical, holy powers - they were what I call the Magicians of the Gods.

These Magicians left a message for us - not a metaphorical, spiritual message, but a direct and urgent warning. What happened before can happen again; what destroyed their world can destroy ours. Those warnings have gone unheeded for millennia. Now, we have the scientific evidence to decode them, but it is almost too late. Within the next 20 years, Earth faces a catastrophe a thousand times worse than the detonation of every nuclear weapon on the planet - a collision with the remnants of a comet big enough to end all life as we know it.

To understand what that could mean, we need to look back at the tumultuous epoch between 10,800 BC and 9,600 BC, which geologists call the ‘Younger Dryas’.

This was a time of extraordinary shifts in the world’s climate. But the most devastating change of all came when the ice caps suddenly collapsed, dumping all the water they contained into the oceans and unleashing a tsunami that swept across continents. As we’ll see, all the evidence suggests this was the result of a comet crashing into Earth. Many Native American tribes describe the devastation in tales passed down through the generations.