Earth could be in danger as the sun's journey through the galaxy dislodges comets and sends them flying between the planets, research suggests.
Scientists have identified a 26 million-year cycle of meteor impacts that coincides with the timing of mass extinctions over the past 260 million years.
The doomsday events are linked to the motion of the sun and its family of planets through the dense mid-plane of our galaxy, the Milky Way.
Gravitational disturbance of the Oort Cloud - a shell of icy objects on the outer edge of the solar system - is believed to lead to periodic showers of comets pouring through the inner region where the Earth resides.
The last of these events is said to have occurred about 11 million years ago, roughly the same time as the Middle Miocene mass extinction.
But according to US geologist Professor Michael Rampino, it might be wrong to assume that we are living in a completely safe era, millions of years away from the next danger period.
He said: "There is evidence that the comet activity has been high for the last one to two million years and some comet orbits are perturbed, so we may be in a shower at the present time.
"That would agree with our position near the galactic mid-plane, where perturbations from dark matter etc. would be expected."
Dark matter is the mysterious invisible substance that surrounds galaxies and can only be detected from its gravitational effects. It is believed to account for more than 80 per cent of all the matter in the universe.
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