At this time, and for some millennia afterwards, the night sky would have been lit up by a bright light caused by dust particles, cometary fragments, and firework displays of meteor storms. The scientists highlight ancient civilisations' preoccupation with the sky. Icons apparently depicting comets were widespread among early civilisations. The new evidence also ties in with ancient prophecies, including the Book of Revelations in the Bible, which appears to describe cataclysmic events involving objects falling from the sky. Dr Napier said the ancient swastika, a symbol of great antiquity stretching back to at least 1400 BC and found from China through India to the New World, may also be a cometary image.
Comets are giant dirty snowballs in space, made of ice and dust.
Unlike asteroids, which are rocky, there is no known upper limit to their size, and the largest can measure several hundred kilometres across. Every 100,000 years or so one of these rare, giant objects enters an orbit that crosses the path of the Earth.