The theory that a giant comet crashed into earth around 13,000 years ago, causing the planet to freeze over and animals to die off is now being called into question as another theory is being put forth to explain the cause of the ice age.

The Telegraph reports that scientists now argue instead that water from melting glaciers disturbed ocean currents and caused worldwide temperatures to drop, resulting in a mass extinction that almost wiped out the human race.

The current widely held belief is that the ice age was triggered by a comet that collided with the earth, sending millions of tonnes of dust into the atmosphere, which blocked the sun and cooled the planet. That theory was formed when scientists found carbon crystals in 12,900-year-old sentiment layers. These carbon crystals were formed by high temperatures and pressure from a heavy impact.

However, researchers from Washington University in St. Louis, MO and the Royal Hollway University of London now say that the crystals have been misidentified and that they are actually common clumps of another form of carbon.